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LB7 6.6 Duramax Common Issues, Problems, and Fixes

GMC and Chevy Duramax LB7 6.6 Diesel Common Issues and Problems

If you have a 2001-2004 Duramax 6.6 LB7 diesel pickup or are looking to buy one, here are some common issues and problems we have run into in our shop.  Over the years these trucks have been really good performers, but they do have some common problems that we see over and over again.

Injectors – It’s hard to have a conversation with any LB7 owner without the topic of injector issues coming up.  The original injectors that came in these trucks had all sorts of issues with cracking.  The symptoms are constant smoke at idle and gaining fuel in the oil.  Unfortunately the best thing to do if you have this problem is to replace the whole set at once.  Injector replacement on the LB7 truck is rather labor intensive and just changing one is usually not worth the risk for the labor costs.  The new injectors available from us and others are updated and do not have the cracking issue.

Fuel Filter Housing Oring Leaks – The Duramax fuel system does not have any sort of low pressure fuel pump pushing fuel to the engine from the tank.  The injection pump sucks all the fuel from the tank.  While we are seeing more and more rusted out fuel lines causing the engines to suck air, nine times out of ten the issues are in the fuel filter head.  Under the primer button there are some orings that fail on a regular basis.  This can produce long cranks and hard starts.

Glow Plug System Issues – Nearly half of the check engine lights that come in for the Duramax pickups are for glow plugs.  The glow plugs burn out over time and can be a real nuisance to remove from the aluminum heads sometimes.  Not only does the threaded metal part of the glow plug seize in the head, but the tips of the glow plugs sometimes bulb making it really difficult to get them out.  Also the metal strips that connect the glow plugs together on each side corrode and break causing issues.  Lastly we replace a fair amount of glow plug controllers as well.  You will usually get a diagnostic trouble code for the cooler when they go bad.

Head Gaskets – As these truck reach the 100,000-150,000 miles we are seeing more and more head gasket issues.  The Duramax has a multi-layer steel head gasket.  When they have issues, they do not typically smoke out the exhaust or get coolant into the cylinders.  What happens is the head lifts a little during the compression stroke.  This allows the layers of the gasket to separate which lets combustion pressure into the coolant system.  The pressure will cause the coolant to be pushed out the coolant overflow.  You can check for a head gasket issue by squeezing the top radiator hose when the engine is running and right after you shut it off.  You should be able to squeeze the hose very easily. If it is rock hard, you have a head gasket issue.  We recommend using ARP head studs for a high clamp load along with one of our head gasket kits to fix it.  It is extremely important to have the heads surfaced flat before putting the truck back together.

Water Pumps – Another issue with the LB7 Duramax is the water pump leaking.  This one is fairly common and unfortunately a huge pain in the butt to change.  Water will seep from the underside of the pump.  Be prepared though because you will have to remove the dampner pulley to get the pump off.  The pulleys are pressed onto the crank and you will need a really good puller to get it off.

Allison Transmission -  The Allison transmission behind the LB7 Duramax to be honest is nothing to brag about in stock form.  If you add a programmer that adds 100 horsepower or more, you will be able to limp the transmission.  The Allison transmission is very sensitive to slip and will derate the power as soon as it detects any slip.  Usually you can just clear the code or restart the truck to get full power back.  Aside from an entire trans rebuild with better parts, we suggest adding an ATS Co-Pilot to help raise holding power.  We have had really good luck adding the Co-Pilot to bone stock transmissions and solving the limp problem with just a programmer. 

If you are having a problem with your 2001-2004 Duramax 6.6 LB7 diesel engine, please feel free to give us a call.  We carry a full line of repair and performance parts for these engines that we install in our shop on a regular basis.  Odds are we have run across your problem before and would be glad to help.  Call us at 1-877-367-9351.