Coming up with an idea for a column is tough sometimes for someone with AMDD (Attention Motor Deficit Disorder—common among people who can’t focus on anything that doesn’t have a motor). So I started rummaging through old notes I’d taken when we first started Diesel Tech magazine
I had one harebrained idea way back then to catalog every common diesel problem I saw in the various shops we worked with. Then we could use it as a resource for reader letters.
However, with AMDD, that idea didn’t last too long. It wasn’t an issue of not coming across engine problems so much as the writing them down part.
Regardless, I’d hate to see the idea go to waste. Somebody might get some use out of my brief spark of office busywork. The following are common problems with GM diesels, how to fix them and what to look for.
LB7 Injector Cups
Out of the four Duramax motor types: LB7, LLY, LBZ, LMM (and LML now) the LB7 was the only model that came equipped with injector nozzle sleeves commonly referred to as injector cups. The injector cups are seated tightly into the cylinder head and held in by the injector via the injector hold down. The problem that is associated with these sleeves is when they lift up out of the head slightly and begin to leak compression, causing pressurization of the cooling system. This is commonly mistaken for blown head gaskets, and end up in costly and unnecessary repairs.
The largest symptom of a pushed injector cup is coolant system pressurization, usually resulting in “coolant puking” from the coolant reservoir after hard acceleration runs. This is usually and early symptom and is the first thing that will get your attention. If not taken care of, the leak can progress until the coolant will puke from the reservoir even at idle and can even allow coolant to start entering the cylinders after the motor has been shut down, causing much more potential damage to a motor through hydro locking, cylinder wall rust and pitting. But if you notice coolant in your oil or excessive crank case pressure, chances are you have a blown head gasket and will require removal of the heads and replacement of the gaskets.
Injector cups can be repaired in most cases by resealing the injector nozzle with red hi-temp 271 loctite. In some cases the injector cup will have excessive heat damage and will need to be replaced and resealed with red loctite.
Lack Of Lift Pump
All Duramax engine types lack one important element to their fuel system, and that’s a fuel lift pump. This is a very important part for maintaining proper fuel system lubrication and longevity. This also creates a road block in the Duramax performance when equipped with chips or tuners. Without a factory equipped lift pump, the Duramax relies completely on the CP3 high-pressure injection pump to do all the work of pulling the fuel from the fuel tank to the injection system. When the CP3 is put under this kind of stress it’s easy to run out of fuel to the injection system and starve the injectors and injection pump of the precious fuel they require to lubricate the system. This will drastically reduce the life of your injectors and injection pump. Not to mention with a lack of fuel comes a lack of performance, so naturally upgrading to an aftermarket lift pump or fuel delivery system is a no-brainer.
Injectors
Unlike problems caused by a lack of fuel, filtration and lubrication, early LB7 Duramax motors had issues with injectors that had high fuel flow return rates. This was caused by defects in the manufacturing process and caused rough idle, decreased fuel mileage and performance as well as producing smoke at idle. Luckily, if you own a 2001-2003 LB7 Duramax, you might be in luck as the factory issued a recall warranty that covers this issue in all 2001-2003 Duramax’s for 200,000 miles or 7 years.
There was a list of Ford and Dodge problems somewhere, but I can’t remember if they’re on a Word document or in my head. I’ll have to sit down in the office one day and hammer out a few page—oooh, did you hear that? Sounded like a built V8 with a GT47 and dual exhaust. What was I saying? Never mind, I have to go check out this truck.
