Does Your Duramax Smoke At Idle? You Probably Need Injectors

This is a customer’s 2002 that he brought in because he thought it might need injectors.  Let us know what you think! (THIS IS AN EXTREME EXAMPLE!!)
LB7 powered (through 2004 Duramax) Chevys and GMCs all suffer from injector failure at some point in their service life.  Many fail as early as 50k miles.  GM recognized this issue and actually had to extend the warranty to 7-years/200k miles.  Bosch redesigned the injector internals a few years ago and essentially corrected the problem; newer injector installations are seeing 150k+ mileage with no issues.

If you drive one, or see one on the road, you can easily spot a truck with injector issues.  At an idle (and worse in gear) these early Duramaxes will haze smoke at idle.  Lots of folks think this is a normal deal for a diesel.  Its not!  That haze is letting you know that one or more injectors are dribbling fuel into the combustion chamber.  Its always a good idea to keep an eye on your oil level.  Failing injectors will often leak fuel into the crankcase, resulting in elevated oil levels and even leaks that appear to be from the rear main seal.

LB7 injectors are also prone to leak on the return side.  This is something you might not see or notice unless you are towing alot.  Owners who experience this problem will have their trucks go into Limp-Home mode when pulling a hill.  The codes will indicate a lack of fuel pressure during enrichment as the fuel is all returning to the tank instead of going into your engine.

GM’s Tech Bulletins basically indicate that if one is bad, replace all 8.  Of course, GM filed for bankruptcy, so dealers were routinely replacing only the injectors that were weak on an injector balance test.  That means that TONS of used Duramaxes are running around with old, leaky injectors in them.  And all of them are out of warranty now.

The LB7 injector job is pretty significant.  The injectors are buried below two layers of valve covers, each with a gasket that is both expensive and generally not saveable.   Each injector also has a return washer that must be replaced.  All of the FICM seals and water seals must also be replaced when performing this job.  Gaskets and seals alone can be as much as $400!  Add 8 injectors at $359 each (dealer price) and this job is pricey.

Left Coast Diesel can knock these difficult jobs out in a couple of days, with significant savings over the dealer.  We use the updated injectors (beware of discount “rebuilds”) and we replace all the seals and gaskets that many other folks might skip.  This means your truck comes back to you more bulletproof than it was when it left the factory!


  1. Randy Duman
    Posted June 23, 2015 at 5:11 pm | Permalink

    My Duramax smokes at idle after the engine has been warmed up. White/blue smoke is exhausted, but like I said ,only after the engine has come up to operating temp. range. I see on line that a fellow recommended changing the fuel filter and filling the new fuel filter with seafoam.He then ran the vehicle for some time and noticed that his Durumax quit smoking. Now he changes the fuel filter when needed,(with a refill of seafoam to clean the injectors). Any comments? My truck dash indicator flashes often that there is water in my fuel system. I have taken the vehicle to my mechanic, and he found no water in my fuel system what so ever. I just chalked it up to my computer giving me false readings. I’m open to suggestions…..Thanks, Randy….

  2. Posted June 25, 2015 at 9:32 am | Permalink

    Randy, Seafoam or something better like the GM Upper Engine Clean system can certainly help marginal injectors. Depending on your mileage and when the last time was that you replaced the injectors, there may not be much you can do. If a treatment does help, it will only last so long. By 100k, the original style injectors are done. The new style last longer. They can leak at idle and cause the smoke, but they also generate high return rates which effect performance. Get the truck checked out and have them check balance rates on the injectors. This will tell the story. GM says (and we agree) that if it needs one injector, replace them all (if they are the originals). A balance rate of +-3 or more is bad news.

  3. Joe
    Posted July 27, 2015 at 5:57 pm | Permalink

    How much in total do you( leftcoastdiesel) charge out the door for a lb7 to replace all the injectors?

  4. Posted July 28, 2015 at 9:04 am | Permalink

    It depends on which injectors you go with. We usually use the Bosch OEM Remans, but we can also do new Bosch or rebuilt injectors depending on budget. Shoot me your contact info and info on the truck and I can have a quote emailed out to you. Thanks!

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