Whether you currently own a Duramax powered Silverado or Sierra, or you have considered purchasing a used GM diesel pickup, the question will cross your mind regarding what problems you may experience with the Chevy Diesel Engines. All told, there are six different iterations of the Duramax diesel engine: LB7, LLY, LBZ, LMM, LML, and L5P spanning from to the present day. Each version of the engine has its own issues and quirks, and some are less problematic than others. Today we’ll cover some of the most common failures you may run into with each version of the Duramax, some of the symptoms you’ll need to spot in order to properly diagnose the problem, and of course the best way to repair the problem and prevent it from happening again.
This is by no means a comprehensive list of all the problems you may run into, so if you are stumped by your Duramax or just need a little more information to help make the best decision on which parts will help get you back on the road, give us a call at Diesel Power Products, and our team of experts will be able to get you sorted out in no time.
Duramax Engine LB7 to
The first Duramax V8 was introduced in and was given the code name LB7. The introduction of common rail injection powered by the Bosch CP3 injection pump made the LB7 Duramax stand apart from other diesels of the day with excellent power and efficiency. As the first batch of trucks started reaching the , mile mark, it became apparent there were some issues with the new engine, and one of the first symptoms exhibited would be a rough idle from the LB7, excessive smoke from the exhaust, long cranking times, and even fuel diluting the oil in the crank case.
We know today LB7 injector failure is a common problem, and because the operating tolerances inside the fuel system are so tight, proper lubrication from the diesel fuel is critical. If there is even the slightest bit of air in the fuel or worse yet contaminants like dirt or rust, you can bet the internal parts of the injectors will wear prematurely and you’ll be doing an LB7 injector change. If you suspect yours are on the way out, the best way to identify which one(s) are at fault, you need to hook up a scanner and read the balance rates. The trucks computer keeps track of how much fuel needs to be added or subtracted from each individual cylinder to make the engine run smoothly, and this value is called the balance rate. If one cylinder is contributing too much or not as much as the rest, the cause is usually a bad injector and the cure is a replacement.
Duramax Engine LLY to
In terms of LLY injector problems, GM had sorted out the internal failures with the ½ redesign, but the LLY Duramax would occasionally exhibit a trouble code for the injectors, but in most cases it turned out to be an issue with the injector harness rubbing through and causing a short or open in the wiring. One of the biggest complaints on the LLY is it has a tendency to overheat, especially when the truck is being worked hard with a heavier trailer or on a hot summer day.
While it may not be the first place you think to look, the stock air intake system can actually contribute to a hotter running LLY Duramax. Many people add a cold air intake with hopes of increasing horsepower and efficiency, but on the LLY you need to take it one step further and add a less restrictive turbo mouthpiece, a part which doesn’t come with most cold air intake kits. When the engine is working hard, the turbocharger is drawing in a ton of air, and the restrictive stock turbo inlet tube can effectively choke the VGT turbocharger causing the compressor outlet temperature to skyrocket, heating up the intercooler, and ultimately raising the temperature of combustion and the coolant temp. However, if you install a stock LBZ or aftermarket turbo inlet, you can let the engine breath freely which will lower air temps and keep the coolant temps under control.
Duramax Engine LBZ to
The LBZ Duramax is often regarded as the greatest Duramax of all time for a few reasons. It was the first to come bolted to the six-speed Allison transmission which provides a lower cruising RPM and greater fuel efficiency when compared to the five-speed on the LB7 and LLY. GM worked out most of the bugs by and the LBZ was much more reliable than its older brothers, and on top of all that, the LBZ Duramax was built right before DPF emissions equipment was mandated in While the LBZ was a stellar engine with very few major problems to speak of, one of the biggest complaints is about something GM forgot to install.
People often ask what is the best lift pump for an LBZ, and truthfully ANY lift pump is better than none at all. The CP3 injection pump sits in the valley of the engine between the cylinder heads and is driven by the camshaft gear, and it has two main jobs: get fuel from the tank up to the engine, and pressurize the fuel to 26,psi and ultimately inject it into the engine. Because the CP3 is doing two jobs at once, it sometimes has a hard time keeping up, but you can help it out with a lift pump. By installing a lift pump with extra filtration from FASS or Airdog you will extend the life of the injection pump and injectors by allowing only the purest fuel into the system, and by feeding a steady supply of low-pressure fuel into the injection pump, it can better focus on its main task of generating high-pressure fuel.
Duramax Engine LMM to
When GM changed body styles with the Duramax, the redesign coincided with some new regulations from the EPA regarding emissions equipment on light duty trucks. Mechanically, the LMM Duramax is almost identical to the LBZ, and if you do a quick search of the web for LMM Duramax problems, you’ll find much like the earlier LBZ it had very few problems related to the engine itself.
One problem can rear its head when you are pushing the power of the LMM to a level GM never imagined, and that’s with the pistons. Simply put, they can crack under pressure. There are a lot of factors which dictate the power level where a piston bites the dust, but it’s usually north of horsepower. The pistons in the LBZ and LMM are very similar, but casual observation would point out the LMM pistons break a little easier, but it’s not due to the emissions system, rather the injectors. The LBZ injector nozzle has seven holes for fuel to spray out of, but the LMM has six which means there are two opposed streams of fuel directly above the wrist pin area of the piston, which causes hot spots directly on top of the weakest area which can lead to cracking. They say an ounce of prevention is worth a pound of cure, and if you want to avoid a costly and time consuming rebuild, it’s advisable to keep your driving habits and tune level at a slightly more conservative setting than “Full Send”.
Duramax Engine LML to
In an effort to keep up with the ever-tightening emission regulations, GM redesigned its Duramax for the model year, and this time the code name was LML. Power was at an all-time high coming in at hp and pounds of torque, and in order to provide this much power while still keeping pollutants low, GM needed to be able to increase the pressure in the fuel system to levels above what the tried-and-true CP3 could safely deliver.
On paper, higher fuel pressure sounds good, but you can’t talk about common LML problems without mentioning the ticking time bomb of an injection pump. A class action lawsuit was even filed against GM for its use of the CP4, alleging the injection pump was designed around European fuels which have more lubricating properties than the ultra-low sulfur fuel which we’re accustom to stateside. As a result (allegedly), the lack of lubrication in the fuel can cause a premature failure of the injection pump, to a point where it won’t allow the LML Duramax to run. You can be driving down the road and everything seems normal, and when the pump fails, the truck just shuts off. At first you might think you can just swap out the pump for another and hit the road, but sadly this is not the case. Because of the nature of the CP4 failure, large amounts of metal shavings are produced inside the pump, and they get sent straight into the rest of the fuel system which contaminates pretty much everything. In order to properly repair an LML after a CP4 failure, you’ll need a kit which comes with a new injection pump, high and low pressure fuel lines (all the way to the tank and back) a fuel filter, a set of eight injectors, a pair of new fuel rails with bypass valves and you’ll even have to drop the tank to clean out any debris.
Luckily there are a few preventative measures you can take to ensure you don’t have to drop the $7,+ to get your LML back on the road after a CP4 failure. Just like an LB7, you can install a lift pump with better filtration which helps to clean air and debris out of your fuel which will minimize wear and extend pump life. Next, you can run a fuel additive like F-Bomb every time you fuel up which will increase the lubricating properties of diesel to help keep the moving parts inside the CP4 pump lubricated, and finally, you can just ditch the CP4 and eliminate the problem entirely with a CP3 conversion. It might seem counterproductive to back-date your LML with a pump that’s been used since in the LB7 Duramax, but the Bosch CP3 actually has a greater horsepower capacity than the CP4, albeit at a slightly lower pressure range. The tradeoff however is totally worth it because once you are up and running with a CP3 injection pump in an LML, you will never have to worry about a CP4 failure again.
Duramax Engine L5P to Present
Just like the LBZ was the best pre-emissions Duramax engine, the L5P is the best post-emissions Duramax. All the problems associated with emissions system and injection pump have been taken care of, and for GM switched suppliers of the injection pump from Bosch to Denso. Mechanically, the L5P Duramax is stout and very few major problems have been reported. One common problem is with the MAP sensor however, as it tends to clog with soot and throw a check engine light, but a simple MAP sensor spacer and a can of electrical cleaner can get you back on the road worry free and prevent the soot from building up again.
Nearly all Duramax powered pickup trucks were equipped with the Allison automatic transmission, with the five-speed version running from to , and the six-speed starting in and running until While it has nothing to do with the engine, it’s worth mentioning some Allison transmission problems because it can be a very costly repair if you happen to damage your trans and need a full rebuild. At a stock power level, the stock Allison usually does an OK job at transferring the torque from the flywheel to the rear differential, but even a bone stock LB7 can put a hurting on the Allison, so you can only imagine what happens when you turn up the wick or hook up an oversized as many truck owners often do.
The five speed Allison is by far the weakest of the bunch, and if you are pushing over horsepower, you’ll probably experience reduced engine power, or limp mode which engages when the TCM detects slippage. The six-speeds have a lot of mechanical similarities with the five-speed, but the few slight tweaks allow the trans to hold a bit more torque. The six-speed can be easily modified with an inexpensive shift kit which will improving the holding power of the transmission to somewhere around the hp mark, and the later + Allison is even stronger. Regardless of which version of the Duramax or Allison you are driving, if you have a heavy right foot and a bunch of modifications, chances are you’ll need to invest in an upgraded Allison so you can put your foot down with no fear. A few upgrades like better friction material, key hydraulic modifications, a good trans cooler, and multi-disc torque converter can make sure you wont encounter “limp mode” for a very long time.
Want to find out more details of known issues and fixes? Check out other resources here:
The 5 Most Common LB7 Duramax Engine Problems L V8 Diesel
Introduced in , the LB7 is the OG L Duramax. This engine is the base platform that todays L L5P Duramax is built off of. Spanning six different variations and nearly 20 years of production, the LB7 has certainly proved to be a reliable and durable platform.
year models were pushing hp and lb-ft. of torque. By the end of its production in , the LB7 got a sizeable power increase to hp and lb-ft. of torque. Given the age of these engines today, the LB7s are popular amongst diesel seekers who are looking for a healthy balance of price and reliability.
Outside of a number of common problems which are mostly resolved today, the LB7 Duramax is a stout engine with good reliability and performance for its age. While the engine isnt necessarily built to be tuned to produce massive amounts of power, it does a great job of being a solid stock work truck.
The LB7 Duramax engine was used in the following vehicles:
- Chevy Silverado HD / GMC Sierra HD
- Chevy Kodiak / GMC TopKick
- Fuel Injector Failure
- Water Pump Failure
- Fuel Filter Housing O-ring Leaks
- Blown Head Gasket
- Overheating (fan clutch problems, radiator gunk)
In addition to the above common engine problems, there are also a few worthwhile to mention problems that affect high horsepower LB7s:
- Crankshafts + connecting rods break at high hp
- Allison transmission enters limp mode at high power levels
1. LB7 Fuel Injector Failure
The LB7 utilizes direct injection which means that fuel is injected directly into the cylinders rather than into the intake manifold where it is then routed to the cylinders. Direct injection requires the fuel to be injected at extremely high pressures. The LB7 uses a 23,psi rail along with a Bosch CP3 injection pump, also known as a high pressure fuel pump. Aside from the carbon buildup caused by DI, the fuel injectors themselves are also very common failure points, even on non-GM engines.
The LB7 injectors had two potential design flaws that could cause injector failure. The first has to do with the internal ball seat inside the injector which would erode and deteriorate from normal wear and tear which would then cause the injector to leak. Secondly, the injector itself was prone to cracking. Both cracked and leaking injectors affect fuel delivery and can cause significant performance issues as air to fuel ratios get out of wack.
Fuel Injector Failure Symptoms
- Engine misfires
- Rough idling
- Sluggish acceleration, overall performance decline
- CELs for lean or rich bank codes
The injector issues were purely the result of a flawed design. Due to commonality of the problem, Chevy designed new injectors and offered a special warranty of 7 years or , miles. In most cases, any LB7 on the road should have had the new injectors installed by now.
However, its worth noting that even with the new injectors, these parts are still prone to failure. Operating at 23,psi, these injectors along with the CP3 pump are under significant amounts of stress. Its not uncommon for the new set of injectors to only last around kk miles.
And unfortunately, this is an extremely expensive replacement. Outside of the injector cost themselves, labor requires about 16 hours of work since they sit underneath the rocker covers and dozens of parts need to be removed to access them.
For those mechanically inclined, here is a DIY guide: http://toxicdiesel.blogspot.com//02/lb7-duramax-fuel-injectors-step-by-step.html
2. Water Pump Failure LB7 Duramax
Water pump failure is common across just about every Duramax out there. Unlike the LBZ water pump failure which is caused by the impeller being made of plastic, the LB7s issues are caused by the coolant side seal on the water pump. The LB7 water pump actually has an impeller which is made out of cast-iron instead of plastic which GM switched over to around on the Duramax L engine.
The water pump has a seal on the side of it which is there to hold the pressure from the spinning shaft inside of it. From normal wear and tear over time the seal becomes defective and will cause a coolant leak. Outside of the coolant leak, the lost pressure of the system will prevent the LB7 from effectively pushing coolant throughout the cooling system, resulting in the engine easily overheating.
LB7 Water Pump Failure Symptoms
- Coolant leaking from engine
- Frequent overheating
- Constant low coolant light / frequent refills
- Noises coming from what pump
- Radiator steaming
Fortunately, water pumps arent super expensive and are relatively easy to replace. There arent any sure fire ways to ensure the water pump doesnt leak or become faulty again, but there are some great upgrade options. Going with a TIG welded water pump is a great option especially for those looking to push some extra power with a tune and bolt-on mods.
Duramax Water Pump Replacement: https://www.thedieselpage.com/duramax/duramaxwaterpump.htm
3. Fuel Filter Housing O-Ring Leaks
The LB7 uses an injection pump, or high pressure fuel pump, to send fuel from the gas tank to the fuel injectors. As part of the fueling system you have a fuel filter and filter head which filters fuel before the fuel is sent through the lines to the injectors.
On the LB7, the fuel lines are occasionally known for leaking. However, the majority of LB7 fuel leaks are caused by the filter housing. The head of the housing uses multiples o-rings to seal the pump. Over time through natural wear and tear these o-rings deteriorate and allow fuel to leak out.
Fuel leaks obviously affect fuel delivery to the engine and can also cause air to get into the fuel lines. As you can imagine, leaking fuel and air in the lines will lead to various performance issues.
LB7 Faulty Fuel Filter Housing Symptoms
- Fuel pump loses prime making the engine hard start
- Low fuel rail engine codes
- Engine misfires, shaky idling, performance issues
Your two replacement options are either to buy a new head assembly or simply buy a rebuild kit and replace the o-rings, gaskets, bolts, etc. Neither of the options are very expensive so I usually recommend replacing the whole assembly for piece of mind.
4. Blown Head Gasket
Head gaskets are common failure points on the LB7 for a variety of reasons. As well get into with the next problem, these engines are known to occasionally overheat while towing. The excess heat is thought to cause this problem some of the time. Additionally, higher horsepower LB7s are more prone to this issue as well.
However, the majority of the time an LB7 blows a head gasket, the design of the gasket itself is to blame. GM used a steel gasket with a containment ring for each cylinder. The containment ring had ridges in it around the cylinder bore. These ridges are thought to be the main contributing factor as the gasket naturally deteriorates over time. The ridge would allow pressure to squeeze between the gasket layers and therefore create a leak. Leaks can either occur outwards, where coolant leaks on the outside of the block, or be internal where it leaks into the cylinders.
Great resource article on LB7 head gaskets and fueling systems: https://www.dieselworldmag.com/diesel-technology/dont-lose-your-heads
5. Overheating Duramax LB7
Another commonly reported problem is the LB7 frequently overheating while towing heavy loads. While overheating can also be caused by a bad water pump, this overheating is mostly thought to be from a faulty fan clutch. The fan clutch, or simply engine fan, is responsible for providing both cooling and heating effects to an engine. While the engine is cold the fan will not spin, allowing the engine to heat up more quickly. Once the engine reaches normal operating temperatures the fan will kick in to assist the cooling system in preventing the engine from overheating.
When the fan fails to kick in at normal operating temps, the cooling system becomes ineffective at keeping the engine at normal operating temps, causing overheating. The second potential cause of overheating on the LB7 is a dirty radiator. Naturally over time the radiator will pick up gunk, dirt, and various other particulates. As this happens, the effectiveness of the radiator decreases which can then result in overheating as well.
As mentioned, this has mostly been a problem for folks when they are towing heavy things. Additionally, it is most common and frequent in summer months when it hotter outside.
Duramax LB7 Problems when Tuned / Running High Horsepower
Since the LB7 is a bit behind the performance curve compared to more modern diesel engines, performance modifications are common. Once you reach the rwhp mark, the LB7 is very prone to bending rods and also snapping crankshafts.
Additionally, more power requires more fueling and more cooling. Running serious power will put a strain on your injectors which are already a common failure point and expensive replacement. Alongside fueling, the cooling system will be more stressed as well and the smaller clutch fans on the LB7 might have a hard time keeping the engine cool. For serious power seekers, youll likely need to add bigger injectors and a lift pump for additional fuel and will need to consider refreshing the cooling system.
Secondly, while the Allison transmissions are fantastic in stock applications, they do not handle additional power very well. The A1k is capable of handling about an additional hp before it will begin limp mode-ing frequently. Even those simply looking to add a tune and some bolt-on mods will probably need to consider rebuilding and upgrading the internals to be able to handle the additional power, especially if youre transmission already has hundreds of thousands of miles on it.
LB7 Duramax Reliability
The LB7 is a great engine, when it is stock. The block and internals are plenty capable of lasting ,+ miles. Most of the injector issues and head gasket faults should be fixed in these trucks now given their age. Water pumps and other maintenance items should be expected on old diesel engines so I wouldnt consider them out of the ordinary or deal breakers when it comes to reliability.
Where the LB7 loses reliability is under additional power. The crankshaft and rods are problem areas under serious power. Additionally, fueling and cooling will become a common failure point as well along with the Allison transmission.
Overall, the LB7 is a strong contender for older diesel engines. For anyone looking for a budget diesel, look no further. Given the age of these engines today, you should expect problems and understand there will be maintenance needed.
Filed Under: DuramaxSours: https://chevytrucks.org/duramax-lb7-engine-problems/
5 Fatal Flaws of the Duramax—and How to Fix Them
It’s been said before, but that doesn’t make it any less true: The L Duramax is one heck of an engine. In stock form and even when substantially modified, GM’s legendary V8 diesel can provide hundreds of thousands of miles of trouble-free use. Still, and just as we exposed the shortcomings of the almighty Cummins, the Duramax isn’t without its flaws—some of them catastrophic. For example, did you know the injection pump on the LML version is prone to coming apart and wrecking the entire high-pressure fuel system when it does? Or how about the fact that the rods in the LB7 and LLY engines can bend with added power and the LBZ and LMM mills are notorious for cracking pistons? Discover the worst failure point(s) of your Duramax in the article that follows, along with how to address it.
1. Snapped Crankshaft
Perhaps the most devastating of all Duramax failures is a broken factory crankshaft. Not only does this mean game-over for the engine, but it results in a truck that’s down for weeks (if not months) and a huge chunk of change missing from your wallet. The failure is most common in higher horsepower engines, but can still occur in moderately modified and even stock power plants. Not specific to one version of Duramax in particular (ex: LB7, LLY, LBZ, LMM or LML), the problem exists across all generations. The crankshaft usually breaks near the number one rod journal due to a combination of excessive rpm and the large external counterweight. A factory firing order that beats up the front area of the crankshaft has also been blamed for imposing undue stress on the crank.
Internally Balanced, Billet Crankshaft
The ultimate fix for the weak factory crankshaft is to replace it with a stronger unit that’s been internally balanced. The billet Callies crankshaft available through Wagler Competition Products is machined from triple heat treated V steel and features reduced rod journal widths for improved strength (which calls for narrower rods). For a more budget-friendly option, a properly balanced Compstar forged crankshaft (also made by Callies) has shown great results in the sub-1,hp arena.
Alternate Fire Camshaft
In an effort to reduce crankshaft fatigue on the front of the crankshaft, alternate fire camshafts are employed. By changing the firing order of the engine (from stock to ), the hard hit at the front of the crankshaft is eliminated and the overall load is more evenly distributed across the crankshaft. Alternate fire camshafts are available from company’s such as Wagler Competition Products, Empire Performance Engineering and SoCal Diesel.
2. CP4 Failure
This one is specific to the LML code Duramax produced between ’’16, which used the Bosch CP high-pressure fuel pump (vs. the predecessor CP3 found on LB7, LLY, LBZ and LMM engines). Unlike the ultra-durable CP3 that came before it, the CP doesn’t possess the same track-record for reliability. Any time water, rust or debris infiltrates the CP (usually due to bad fuel or lack of maintenance) it’s prone to either seize up or come apart internally. Unfortunately, the latter scenario plays out more often than seizures do. Typically, the roller lifter (or bucket) that rides on the CP’s shaft (the part that’s driven up and down via the plunger) fails due to lack of lubrication or debris hampering its ability to operate in an unobstructed manner.
Buy Good Fuel
When a CP self-destructs, metal debris is sent through the high-pressure fuel lines, the injectors and the fuel tank. As you can imagine, it’s both labor intensive (a 30 hour job) and expensive (as much as $10,) to fix. As you might’ve guessed, water and/or dirt contamination isn’t covered under GM’s warranty, so you’ll likely be footing the bill if your CP goes south. However, there are measures you can take to keep the pump happy and healthy, the first being to always buy your diesel from a high-traffic, reputable filling station that’s known to dispense good, clean fuel. Second, always change the fuel filter at or before the recommended service interval.
Add a Lift Pump
Like all Duramax engines from ’’10, the LML was also void of a lift pump from the factory. This means that not only does the CP have to pressurize fuel as high as 29, psi before sending it to the rails, but it also has to pull its low pressure fuel from the tank. We don’t exactly know what the CP requires for low-pressure fuel supply in the LML Duramax application, but in the case of the L Power Stroke—an engine that also utilizes the CP pump but that receives its fuel from a factory-installed lift pump—Ford prefers that it sees 55 to 60 psi. By installing an aftermarket fuel supply system from company’s like FASS or AirDog you’re ensuring your CP sees steady low-pressure fuel supply and adequate lubricity at all times.
For utmost peace of mind, the CP can be ditched in favor of the tried and true CP3. Various aftermarket kits come with everything you need to complete the conversion, mechanically (note that a few ECM tweaks will be required, too). On top of being known to last hundreds of thousands of miles without any major issues, the CP3 flows roughly percent more fuel volume than the CP, so there is also a slight performance advantage to sending your LML’s injection pump “back in time.” Companies such as Fleece Performance Engineering, H&S Motorsports, HSP Diesel, Wehrli Custom Fabrication and many others offer CP3 conversion kits.
3. Bent Rod(s)—LB7/LLY
We’ll be honest, experiencing a tweaked connecting rod in an LB7 Duramax (’‘04) or LLY Duramax (’’) is almost exclusively reserved for engines making double the factory horsepower (or more). However, because better than one in four diesel-powered GM trucks is graced with an electronic power-adder, and the fact that this is an enthusiast site, all of you should take note. So what causes the rods to shrink? In a word, torque. Thanks to a compression ratio (the highest of any other engines in the Duramax lineage), extreme amounts of low-rpm cylinder pressure (i.e. torque) can be present when you’ve more than doubled the factory horsepower and torque rating. This stress is directly imposed on the pistons, the rods and the crank—but the rods are the weakest link in LB7 and LLY engines. Luckily, the rods found in these two engines are forged steel, which is to say that they bend long before they think about breaking. This means you’re usually not in need of a whole new block when this failure strikes.
Other than dialing back the tuning or scrapping your performance plans altogether to save the factory connecting rods, aftermarket units are in order. CP Carrillo, Wagler Competition Products, Manley Performance, Brian Crower and Howards Cams all offer aftermarket Duramax rods. In addition to its competition-ready rods (rated for 2,plus hp), Wagler also offers As-Forged units, which are the most budget-friendly Duramax rods in the diesel industry. Conservatively rated to handle 1,hp, they’re forged from ACQ, shot-peened to reduce stress risers, come standard with ARP 7/inch rod bolts and retail for $1,
4. Cracked Piston(s)—LBZ/LMM
Even though the ’’10 Duramax's are equipped with slightly stronger, forged-steel rods than what was used in the ’’05 engines (LB7 and LLY), the problem moves upward, into the pistons, on the LBZ and LMM engines. Most cracked piston scenarios play out at power levels well beyond stock (roughly to rwhp for street-driven, ’‘10 trucks), but we’ve also seen it occur on bone-stock Chevy and GMC HDs. Low-quality castings from its suppliers and a reduced amount of meat present in the wrist pin area (thanks to the use of wrist pin bushings) are to blame for factory piston failure. In most cases, the cast-aluminum piston cracks along the center line of the wrist pin, as shown above.
Depending on the type of engine you’re building, aftermarket piston options range from mild to wild. For utmost affordability, some enthusiasts opt for de-lipped, LB7-based pistons for subhp builds, while others take comfort in the performance cast units manufactured by Mahle Motorsports or the reworked, oval bowl Mahle units from John “Fingers” McElravy. For many all-out, competition-type builds, forged pistons from Diamond Racing are known to get the call.
5. Leaking Injectors—LB7
One thing the ’’04 LB7 Duramax is notorious for is injector failure. The two primary failure points of the factory injectors are internal cracking of the injector body itself and corrosion-induced failure of the internal ball seat. The solenoid style Bosch units found in the LB7 employed a non-hardened internal ball seat to seal the injector. By comparison, later versions of injectors would utilize a hardened, chrome-plated ball seat and—not surprisingly—benefitted from much improved durability. Over time, this ball seat erodes and no longer fully seals. When an LB7 injector begins to leak, you’ll notice the truck hazing at idle and you’ll also be able to observe abnormally high injector balance rates (the amount of fuel each injector contributes to maintain a smooth idle) with the appropriate diagnostic equipment. To add insult to injury, a leaking injector means a considerable amount of fuel is making it into the crankcase.
Located underneath the valve covers, there is nothing cheap about replacing an injector on an LB7. For this reason, most shops recommend you replace all eight injectors as opposed to doing them one at a time. LB7 injector replacement performed at an independent shop typically calls for hours worth of labor and roughly $3, No matter where you take the truck for the job or whoever performs the work, make sure you install brand-new, genuine Bosch injectors. The latest Bosch versions feature an improved body (no cracking), a hardened, chrome-plated ball seat (no leaking) and DLC coated nozzles for unmatched long-term durability.
Written By: Lawrence LT Tolman
Back around the turn of the century, General Motors teamed up with Isuzu and designed a revolutionary new powerplant specifically for use in pickup trucks. The joint venture (and resulting engine) was known as Duramax, and the LB7 was the first of many models to come. It’s a liter, common-rail injected, valve, V8 turbodiesel which put out hp and pounds of torque in its first year, and for the final year of ‘04 the LB7’s output had grown to hp and pounds of torque. When the Duramax powered HD trucks were brand new, critics were impressed with the power and response as well as the fuel mileage, but more than anything they were blown away with how quiet the common rail injection system was compared to the mechanical diesels of the time. Today if you want to get your hands on a Chevy or GMC powered by the LB7, they can be found for as little as a couple thousand bucks if you want a beater, but even clean, medium mileage trucks can be had for around twelve thousand bucks. At first when the trucks were new, the LB7 was found to be very reliable, but as the years wore on and miles accumulated, there were a few common issues that popped up.
It’s a fact of life any year-old trucks will have problems that need to be addressed here and there, but rest assured its nothing that can’t be solved when you own a Chevy. With a little careful maintenance and repair, your aging pickup will give you many hundreds of thousands of miles of service. Today we’re taking a closer look at the LB7, some of its shortcomings, how to spot problems in advance, and of course, how to fix them.
The one issue the LB7 is best (or worst) known for are the fuel injectors. There are several causes of the failures, and the issues were so common, GM covered the injectors with a special extended warranty for , miles or 7 years after the vehicle was placed in service. For most buyers the first set of injectors will likely have already been taken care of since the failure usually occurs between , and , miles. The bad news is, some of the replacements from GM are known to fail again, so the truck might need a second or even third set depending on how many miles it’s racked up.
The first question a potential buyer will ask when looking at an LB7 truck is how do I tell if the injectors are bad? While a service record or invoice is a good start, usually you won’t get that lucky. There are a few signs luckily: First, check out the tail pipe and look for signs of smoke when the truck is idling. There shouldn’t be any. Second, check the engine oil level on the dipstick: if it’s over the full mark and smells like raw diesel fuel, there’s a good chance the oil has been diluted with fuel from a sticking injector. But the third and most accurate method of checking an injectors health comes from reading the cylinder balance rates with a scan tool. A balance rate is the amount of fuel that has to be added or subtracted from each individual cylinder to make the engine run smoothly, so if an injector is failing, its balance rate will be much lower or higher than its siblings. With the truck up to operating temperature, the acceptable range is ±4 mm3 in park and ±6 mm3 when in gear at idle with your foot on the brake. If you have one or more injectors with a total fuel rate that falls outside of the accepted range, chances are it’s going to need a replacement.
It sounds simple enough to just swap out a failed injector for a new one and be on your way, but it’s not exactly a repair you’ll make on the side of the road in 20 minutes. The injectors are buried underneath the rocker covers, and there are about a dozen other parts in the way. Based on the labor time it takes to replace the injectors, (book time is around 16 hours) many owners decide to replace the entire set of eight at once since labor costs would be duplicated if you had to come back later to replace the ones you skipped. If your final goal is anything less than hp, then there’s no reason to upgrade to a larger injector, so a genuine Bosch replacement will be your best bet get you back on the road. They are an updated design which eliminates the failures the original versions are known for, so you won’t have to worry about another failure. But…. If you plan on stepping up your power gains in the near future, it might be a worthwhile investment to install a slightly larger set instead.
If you’re lucky enough to have a set of eight injectors that are working just perfectly, or you just had them replaced, how do you keep ‘em running like new? In one (or two) words, it comes down to fuel quality. Modern ultra-low sulfur diesel doesn’t have the same lubrication properties as older blends of fuel, plus when air becomes entrapped in the fuel, the tiny bubbles can cause accelerated wear under the extreme conditions inside the injector. By running a quality fuel additive like F-Bomb each time you fill up, the lubricity of the fuel is increased, and the injectors are kept clean and healthy, which leads to a longer service life. Plus, you’ll see an increase in power and fuel economy. Additionally, running a lift pump with a good filtration system like the FASS Titanium Signature Series will remove water and air from the fuel along with any small particles of dirt, so nothing but clean pure fuel makes its way to your engine, keeping your injection pump and injectors protected. Once you have the injectors crossed off the to-do list, there aren’t a ton of major issues that plague the to GM’s, but there are several smaller ones which you should be aware of if you own or plan to own an LB7, and the next most common issue lies with the transmission.
Another industry first GM was able to take credit for was installing a medium-duty transmission into their pickups. The Allison A was designed for trucks and equipment, but GM adapted it to the LB7, and it has been used in every Duramax produced since (except of course the ZF-6 manual versions). The Allison found behind the LB7 was a 5-speed model, and it will live a long life when used behind a stock powerplant. A few minor upgrades that will keep the trans happy revolve around keeping the fluid clean and cool, since ATF is the lifeblood of any automatic transmission. First, regularly changing the external spin-on filter is a super easy way to keep the fluid clean, and you should do it every other oil change. They say transmission life expectancy is inversely proportional to the temperature of the fluid, and heavy use like towing (and racing) can generate a lot of heat and shorten the lifespan of your friend Allison. To combat this, a larger transmission cooler will remove more heat from the fluid, and a deeper extra-capacity transmission pan will hold more fluid to absorb the heat from the transmission, plus the aluminum construction radiates heat for additional cooling.
Regardless of how strong they are behind a stock engine, when you get power hungry the Allison 5-speed has a hard time transferring the power to the ground. In short, the holding power of the stock clutches just isn’t sufficient for a high-performance application, and once you get to about horsepower over stock, you’ll begin to experience some clutch slipping. There are a few dead giveaways that will let you know if you’re about to experience trans problems. If you are on the throttle and the engine RPM suddenly rises but you don’t accelerate or the truck goes into reduced power, also known as limp mode, you have received your warning. And if you slip the trans once, the likelihood of it slipping again goes way up and things will continue to get worse, so you have two choices: turn down the power or install an upgraded transmission. The good news is whether you have a tune-only truck or a fully built monster, you have a solution. A great place to start is ATS, and their stage one transmission has what it takes for the stock or mildly tuned truck that tows heavily, or if you need a lot more holding power, you can upgrade to their stage six version, which is good for +hp, and of course they have an option for every power level and application in between.
As we said earlier, the LB7 powered HD Sierras and Silverado’s are very reliable, and many you’ll find on the market have well over , miles on the original engine. However, there a few small things that will have to be replaced along the way, and for GM, their IFS front ends are at the top of that list. While they do ride smoothly, there are a lot of moving parts that wear out, like tie rods, pitman and idler arms, steering boxes, ball joints, and wheel bearings. A stock height/tire size truck might make it to k miles or more on the stock parts, or a lifted truck might last half as long (or less) depending on how the truck is used. Either way you can count on a full rebuild of the IFS at some point, and the warning signs are uneven wear on the front tires, play or wandering in the steering, or excessive vibration coming through the steering wheel. Since the stock steering parts are a bit too small to begin with, it’s a good idea to make a few upgrades as well. Simple tweaks like PPE Stage Three tie rods can strengthen up the steering greatly, and when you combine those with the center link brace, your steering will be much more precise and stronger than before, and it will last for many miles to come.
Along the way, you’ll encounter a variety of smaller maintenance items on your LB7 truck, from oil leaks in the transmission cooler lines to the transfer case oil pump rubbing a hole through the side of the case, but the best thing about an older GM truck is the parts to fix the issues are inexpensive, and in most cases, you can permanently solve the issue, rather than simply replacing failed items with more stock parts. Two such upgrades for an LB7 are the Fleece Performance transmission cooler lines which are a much stronger design than stock, and the Merchant Automotive transfer case pump upgrade kit.
High Performance Build
Once you’ve taken care of all the maintenance items, you could just leave well enough alone and ride in your bone-stock LB7 until the cows come home. However, one question always comes up when talking with your friends, and that is “how much power can the stock engine safely handle?” The answer is never a simple one, as there are a lot of variables, but each engine has a general range where it starts to fail. For the LB7, that number is somewhere around to horsepower at the wheels. Some can hold more, and some have failed with less, but that’s a good ballpark. Once you get much beyond the threshold, pistons can start to crack from the cylinder pressure, head gaskets can start to fail, and connecting rods can eventually bend. The crankshaft and block are (basically) bulletproof, and when it comes to crazy power numbers, you can reach for the stars. In fact, some of the power records for a Duramax have been made by an LB7.
Go Ahead and Try it at Home
Overall, the LB7 is a very reliable and efficient engine with exception to the injectors faults, but beyond that, the truck will only need basic maintenance and last for several hundred thousand miles. Just about any issue that might come up has readily available and affordable solutions, and they’re not hard to work on. You do have to look out for rust on the trucks, as the GMT trucks were prone to rotting away at the rocker panels and above the rear wheels, especially if you live in the rust belt. From a high-performance aspect, the LB7 is also a great candidate for a build, and the best part is, you likely got such a good deal on the truck when you bought it, you’ll have some money left for fun parts to make the truck go faster. Whether it’s in pristine condition or just an old beater, if you’re still rocking an LB7 every day, you deserve a gun salute, since there’s nothing more American than an old-school HD pickup racking up the miles.
Issues 2003 duramax
Fuel Starvation and/or Air in the Fuel Lines
The Duramax diesel is susceptible to fuel starvation and getting air in the fuel lines. This can be contributed to the fuel filter housing design and the fact that the Duramax does not use a lift pump. Rather, the high pressure fuel pump (injection pump) is responsible for vacuuming fuel from the tank. It is quite common for the fuel filter housing to develop a small crack or let air seep in due to a bad housing o-ring or water-in-fuel sensor o-ring. It can also be relatively difficult to prime the fuel system once air has been introduced into the system, such as when the fuel filter is changed. The to LB7 fuel filter housings seem to be the most prone to problems.
Water Pump Failure
Water pump failures for Duramax engine are somewhat common. It is not unlikely that a water pump will need to be replaced in the 80, - , mile range. This seems to be inherent of the factory water pump design.
Overheating issues with the Duramax diesel seems to be a hit-or-miss problem; some owners experience it, while others never will. Regardless, it's more common with the Duramax than other engines. Overheating typically occurs while towing in the Summer months, and is most prevalent in or earlier models (+ models received a larger radiator and fan). Overheating often occurs as a result of a fan clutch failure, preventing the engine fan from providing supplemental airflow as necessary to keep the engine from overheating. There's some speculation that a dirty/clogged radiator also contributes to the problem, as the grime that builds up on the radiator over time reduces its effectiveness as a heat exchanger. A water pump failure (which is relatively common) will also likely result in overheating.
Premature injector failure was a critical problem for the to model year Duramax LB7. GM corrected the problem with an updated injector design and even extended the warranty on the new injector design to 7 years/, miles. If you are buying a used truck, be warned that not all engines have been retrofitted with the new injector design. The design flaws of the original LB7 injectors have not been characteristic of later injector designs. However, Duramax injectors (in general) seem to be relatively sensitive to contamination and may fail prematurely if proper maintenance is not performed at regular intervals.
Injector Harness Chafing
It is extremely common for the injector wiring harness to chafe over time. This can cause a number of issues if the wires become exposed, including a no-start or rough running, lack of power situation. The associated trouble codes will usually reveal which injector(s) are affected and will relate to an "open circuit" condition. Example: "Injector circuit open, cylinder 7". To relieve this problem, the wiring harness (or affected portion of the harness) will need to be replaced/repaired. Often, you can verify the problem by wiggling the wires around the injector. If the problem goes away (even momentarily), you've identified the affected zone.
Glow Plug Failure/Concerns
Glow plug failure was a concern on the model year LBZ and LLY Duramax models, but the problem should have been long corrected for owners of these years. The concern was that the glow plug module would over cycle the glow plugs, creating a scenario in which the tip of the glow plug could actually deform and/or break off in the engine. In such an instance, catastrophic engine damage could (and likely would) occur. GM identified the problem and has reprogrammed the glow plug module to eliminate this risk.
Aluminum Cylinder Heads
The truth of the matter is that there are no concerns regarding the aluminum cylinder heads on any generation of the L Duramax. With over 1,, Duramax engines on the road today, the aluminum cylinder head design has yet to be identified (with any credibility) as an inherent problem for Duramax owners. The concept of aluminum cylinder heads on a diesel engine, which is subjected to relatively high cylinder pressures, is more worrisome than the reality. The head bolt design has proved sufficient in preventing the cylinder heads from lifting under the conditions they are subjected to (at stock power levels). In fact, the Duramax is no longer the only engine featuring aluminum cylinder heads; Ford's L Power Stroke also utilizes the lighter material and their design has proven equally reliable. When the Duramax was first introduced, many were skeptical about the aluminum cylinder heads, but there is no need to worry.
PCV Design - Turbocharger Oil Ingestion
The Duramax PCV design vents the crankcase pressure into the intake. As a byproduct of the process, engine oil is introduced into the turbocharger. Over time, this engine oil coats the inside of the intercooler and intercooler tubing. The primary concern is that large quantities of oil settle in the intercooler boots, causing them to rapidly degrade. There are several aftermarket products on the market that reroute the PCV line so that it vents into the atmosphere rather than into the intake, and a number of "DIY" methods of remedying the problem.
Allison Transmission Limp Mode
The Allison 's limp mode feature is a safeguard against catastrophic transmission failure. In reality, it's less than ideal for many situations. When the Allison transmission senses an abnormal amount of slip in the transmission, it enters limp mode. While in limp mode, the transmission will lock in 3rd gear, the torque converter will remain unlocked, and the transmission will not be able to operate in reverse. It's great to have such a fail safe, but in many instances the limp mode is activated when it's not entirely necessary. It usually occurs under heavy load (such as towing, down shifting to pass, etc), and is extremely common in tuned trucks (even a mild performance increase can cause enough slippage to trigger limp mode). There is concern that the transmission could slip in high gear and be forced into 3rd gear suddenly, causing a spike in engine speed. To take the transmission out of limp mode, clear the engine trouble codes using a scan tool. Some owners have also suggested that turning the engine off and cycling the key to the on position several times will take the transmission out of limp mode. If your transmission experienced limp mode, it's likely on the verge of needing a rebuild in the near future and should not be ignored.
LML DEF/SCR System Woes
The Duramax LML was introduced for the model year featuring the most sophisticated emissions system yet. The latest additions included the selective catalyst reduction (SCR) system, which requires a constant supply of diesel exhaust fluid (DEF) to inhibit the reaction that converts nitrous oxides into more impregnable compounds. The system relies on various sensors plumbed into the exhaust system in order to accurately control the injection of DEF into the catalyst. Not particularly surprising, the new system proved littered with problems, most of which would be ironed out by the production of the model year engines. By far and large, the most common problem was the reoccurring failure of one of the systems two NOx sensors. Additional problems included DEF level sensors, DEF pumps, and DEF tank heaters (which often allowed DEF to freeze in extremely cold environments). Owners of model year trucks may or may not be covered by an extended warranty on NOx sensors, as the widespread frequency of problems prompted GM to increase the warranty period for these parts for what they consider "affected trucks".
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