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Discussion Starter · #1 ·
This is going to be a long post.. :oops:
I hope you guys can help me with my truck.

A while back my LLY started to have rough idle but no knocking, so I changed the CP3 pump regulator and the EGR because it was done. After that it was good for a month or so. Then it started idling rough again but also with the sound of the injectors clattering when driving, and engine was shaking at idle. I called a GM guy here in DK and he said that he could check if there were any updates from GM, and there were. 1 for the engine and 1 for the transmission, and if that didn't solve the problem he had a Diablo tuner and we could try to increase the fuel pressure and a bit more HP. So he did that and it ran better with no clattering or shaking.
Everything was fine for almost a year and it started again, but this time I'd had it. So I took the injectors out and took them to a guy I know at Bosch and he ran a test and told me that they were garbage and had been delivering twice as much fuel as they was supposed to.
Ordered new injectors and installed them (still have the Diablo tune in it) and it sounded so good and drove really great for a month - then it started to give the signs of blown head gaskets, so I tore it apart again and put new gaskets, glowplugs, thermostats, waterpump, FPRV, fuel filter, adjusted valves, renovated the turbo and so on. Put it back together and everything worked, unless the injector sound. But now it had a fizzing noice from the back of the engine and something was wrong with the exhaust pipe. :sick:
I then took the cab and bed off and just went over everything and also installed an Airdog 165 liftpump.
I got the truck back together yesterday, fired it up and damn the knocking was bad, even when I turned the pressure down to minimum! - I shut off the lift pump and it went back to normal but still has that 'injector not getting enough fuel' sound.
Went to the GM guy this evening and he removed the Diablo tune and got it back to stock. Now the 'injector not getting enough fuel' sound is even worse when driving and also it stutter sometimes, and if I turn on the lift pump, it doesn't knock as much as before with the diablo tune but it sounds different, almost as if the pressure is to high, but it doesn't trow a code.

I'm really close to pulling my hair out..
This truck is the worst I have ever had - mostly because the previous owner didn't know a first thing about mechanics, but still did some work on the engine, that was carried out in a less than perfect way, to say the least.
Does any of you have an idea about what's wrong?
And shouldn't the lift pump just be a plug and play and not change the engine sound?

It has 295.000 km / 183.000 miles on it.

3,049 Posts
I have no idea what might be wrong with your turck, sorry. However, if you look on the diesel truk forums, you will see many people having problems use a FASS 150 pump. I can't say that they're the cause of every problem, but many people have reduced the pressure to about 5psi and their trucks run much better. If the pump puts out too much pressure, the LML trucks seem to be quite sensitive to this. And if the 150 really pumps out 150 gph, much of that is getting recycled back into the tank. I think my cheap aftermarket pump (Airtex E8153) puts out 35 gph and it seems to work just fine in every condition I have used it in. Never a problem pulling my 12K fifth wheel.

One thing you can try that might help you see if the lift pump is the problem is to put some diesel fuel in a gas can, and run your engine out of the diesel in the gas can. Many people do injector cleaning in this manner and there are writeups on this forum and others and on Youtube showing how this is done. You truck might run better or maybe not. If better, it points to either lift pump or vacuum leak somewhere between the tank and the engine fuel filter.

In any case, I hope someone will have a good suggestion or two that will help make your truck run better.
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