Hi,
I just had the injectors and fuel pump housing replaced on my truck. It's a 2001 GMC 3500 Duramax with 70k miles on it. The dealer did the work for free since GMC has had problems with injectors on these models.
I picked up my truck Friday and it works well, except for one thing: when coming to a stop, foot off the accelerator, no braking, there is a definite fluctuation in the idle (the rpm indicator doesn't show it, but you can definitely hear it). It did not do this last week before the work was done. I did not notice any loss in power, or anything elso out of the ordinary. It only does it when slowing down and only from 35 to 20 mph. At 20 mph the transmission downshifts and the rpm's stabilize again. I just took it back and went for a drive with the diesel mechanic who worked on it. He heard it and said it was strange, never ran into something like it. He looked on his computer for an explanation but couldn't find anything related to it. I left it there, he ran some tests and found the actual fuel rail pressure to be fluctuating approx. 100 psi. He said that this amount of fluctuation is normal. He also called TAC (I think GMC support) and they told him to recommend that I use a fuel additive to burn through the current fuel and then try a different brand of diesel and see what happens. The thing is, I've always used this brand, and this hasn't happened before.
If anyone has any advice for me as to what might be at fault here I would greatly appreciate it.
Thanks again!!

 

Sounds like a bad fuel pressure regulator, mine did that for a long time and it took 2 months for it to throw a code at me which was a P0089 Fuel pressure regulator performance. Still haven't replaced it, but i know its going bad. Some two-stroke(one quart) oil in the tank will smooth it out, worked for me, the lopey idle went away.

---AutoMerged DoublePost---

Alsoo when adding the two stroke oil, add the regular amount of fuel additive as usual.

 

I have seen this many times on my DMAX due to running on SVO...most of it can be fixed with some custom tuning.....but since your truck is stock I agree it should be running right ! Do you have a code reader?

 

No, I didn't realize I could check it myself... Where do I get a code reader and is it fairly easy to use??
Thanks.

 

Have him check for a reflash.

 

You can stop by an auto zone and have them read it for you, keep us up to date

 

Update?

 

Yes....Update?

 

I think this one is solved.

 

Closing for now. We can reopen this is problem returns.