LMM Duramax Problems To Expect

LMM Duramax is a pre-emissions diesel engine that is popular for its sturdy motor and improved fuel economy. However, common LMM duramax problems you may experience are clogged DPF, cracked pistons, faulty fuel injectors and fuel dilution.

If you can maintain the LMM Duramax diesel engine properly and occasionally take it to a mechanic shop to fix minor issues, your LMM Duramax engine will last up to 40,000 miles.

LMM Duramax Engine Common Problems

There are some common lmm duramax problems you may experience after owning a vehicle with an LMM Duramax engine along with simple solutions:

1. Clogged Diesel Particulate Filter

A diesel particulate filter (DPF) isn’t a popular function of the LMM Duramax engine. Though GMC redesigned DPF on the 2011 model, still it has some issues. The DPF on the LMM Duramax engine can clog or fail due to frequent incomplete cycles and cause reduced fuel economy. DPF can also get clogged due to collecting excessive debris and trash.

Clogged Diesel Particulate Filter

Ash and soot build-up in DPF clogs the diesel particulate filter, limits exhaust flow, and causes rough running and limited performance. If you drive your vehicle with an LMM Duramax engine in heavy city traffic and frequently make short trips.

It can interrupt the active and passive regeneration cycles. So the DPF can get blocked. A block DPF can’t function efficiently and can produce black smoke emissions and disturb the combustion process of the engine.

Solutions

If you want to avoid this issue, you must operate your vehicle with an LMM Duramax engine at highway speeds and let the cycle take 30 minutes to complete. You should also avoid start and stop driving conditions particularly when the engine reaches full operating temperature.

You can also pour full synthetic low-ash engine oil on your LMM Duramax engine to avoid causing excessive ash and soot buildup. But if the DPF fails completely, you will need to replace it which can cost up to $3000.

2. Air in Fuel Lines     

2001 to 2016 LMM Duramax engines have air in fuel lines issues and struggled to operate the fuel system properly. Air enters the LMM engine’s fuel line as these engines don’t have an electric low-pressure lift pump that delivers fuel from the tank to the injection pump.

These engines use mechanical fuel pumps to supply fuel from the tank. Air can also enter the fuel line due to cracks in the fuel filter housing.

Air in Fuel Lines

Solutions

If you want to remove air from the fuel line, turn the ignition on with the engine off and then turn off the ignition. This will turn on the fuel pump for a few seconds and allow the fuel pump to push air through the line and back into the fuel tank. But if the cracked fuel filter housing allows air to enter into the fuel line, you will need to replace it.

3. Low Fuel Rail Pressure

If you have a 2008 GMC 3500 Sierra with an LMM Duramax engine, you can have a low rail pressure code like P0087 on the dashboard. LMM duramax engine causes this issue particularly when carrying heavy loads on mountains.

Low rail pressure code can come out on an LMM Duramax engine due to a bad lift pump, faulty fuel pressure sensor, or damaged fuel pressure regulator. Air leaks at the fuel filter housing can also trigger low rail pressure codes.

Low Rail Pressure

Solutions

If you want to bypass low fuel rail pressure code on the LMM Duramax engine, you will need to check the fuel pressure sensor, fuel filter, lift pump and pressure regulator and replace the faulty part. If these components are in good condition and you still notice the code, you’ll need to check and replace the fuel pressure relief valve.

4. Cracked Pistons

The damaged piston is another common problem of LMM Duramax engine. Pistons endure the effect of the intense temperature and pressure within the combustion chamber. However, pistons can get damaged due to excessive heat, crack, and fail eventually.

This is because the fuel in the LMM Duramax engine sprays directly over the center of the piston which gives the piston exposure to intense heat.

Cracked Pistons

Solution

You will need expert mechanics’ help to troubleshoot and fix the bad piston.

5. Fuel Dilution

Fuel thinning is a serious problem for the LMM Duramax engine. If you pour raw fuel into the exhaust stream incorrectly or use the wrong oil, it can cause fuel dilution problems in LMM Duramax engine. For example, if you use high-quality synthetic engine oil on your LMM Duramax engine, it can weaken the engine oil.

If you change your driving habits or repair fuel leaks, it can also make the fuel weaken. Even if you don’t determine the right engine oil change interval and change oil after the fuel dilution passes 5%, it can also make the oil thinner and cause lots of performance issues.

Solutions

If you want to avoid fuel dilution problems in the LMM Duramax engine, change oil every 5000 miles or 8000km. run your car 50 to 60 miles strain once a month to turn off impurities and avoid causing fuel dilution. You can also use GF6 oil to fix fuel dilution problems on the LMM Duramax engine.

6. Fuel Injector Issue

Fuel injectors help deliver the right amount of fuel at the right time in the engine. However, fuel injectors can collect debris, get clogged and disturb the performance of the engine. If the fuel injector gets damaged on the LMM Duramax engine, you will notice excessive smoke from a tailpipe at idle. A bad fuel injector can also cause rough idle and power loss issues on the LMM Duramax engine.

Fuel Injector Issue

Solutions

If the fuel injector on your LMM Duramax engine is clogged or damaged, you will need to remove it from the engine and clean it professionally. If it doesn’t work, you will have to replace the faulty fuel injector which can cost around $150 to $400 based on your vehicle’s make and model.

7. Reduced Power

Some 07.5 LMM Duramax engines cause reduced power issues and trigger the P0090 code. It can mostly happen due to broken wire in the fuel pressure regulator.

Solutions

You can troubleshoot the reduced engine power issue on your LMM Duramax engine to determine the underlying issue. In this case, perform an OHM test on FPR and make sure it has around 3 to 5 OHMs. You can also check the FPR wiring.  If you get different OHM results, replace the FPR wiring.

Is LMM Duramax Engine Reliable?

Yes, LMM Duramax engine is one of the most reliable engines that comes in GMC vehicles. This engine is quite the same as the LBZ and doesn’t have a major issue. Though the DPF of the LMM Duramax engine can scare you, it’s cheaper to delete or replace. If you drive the vehicle, maintain the engine properly and successfully fix the simple issue, you can enjoy up to 150000 km longevity without any major issues.

If your vehicle has a tow tune and eco tune, use eco tune in stop-and-go traffic to retain the longevity of your LMM Duramax engine. The LMM Duramax engine is popular for its quiet performance, ability to handle heavy trailers, and long-range remote start.

However, the intense operating temperature can reduce the longevity of the LMM Duramax engine and its related components. If you want to enjoy the best performance out of the LMM Duramax engine, avoid the 2007 to 2012 model years.

FAQs on LMM Duramax Problems

How Long Does The LMM Duramax Engine Last?

The longevity of the Duramax LMM engine depends on the way you maintain the engine and take care of it. On average, the LMM Duramax engine lasts up to 300000 miles while some owners claim that they enjoy up to 400000 miles with the LMM Duramax engine.

How Much HP Can An LMM Duramax Engine Handle?

LMM Duramax engine is designed with a high-quality turbo, injectors, and a high-pressure fuel pump. This engine can support up to 530 to 540 HP.

What is The Common 2008 LMM Duramax Engine Problem?

Most owners of the 2008 LMM Duramax engine complaint that this engine has damaged pistons. When pushing the power of the engine, it causes a crack under pressure.

Final Words

Whether you are buying a Chevrolet or GMC vehicle with an LMM Duramax engine, you should understand the common LMM Duramax problems. Though LMM Duramax doesn’t cause any major issues, its DPF, weak airline, piston, and fuel injectors can sometimes irritate you and cause various problems.

So if you own a vehicle with an LMM Duramax engine, you may need to visit a mechanic shop periodically to keep those parts in good condition and avoid drivable issues.

Dennis Walton is a professional car mechanic and part time automotive blog author. He lives in Denver, Colorado known for his expertise in all types of car engine. Dennis is passionate for cars and established himself as a trusted authority in the automotive industry. He shares critical car problems and solutions on How We Drive blog.

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