Surge at Idle

[dmaxtruck]

Hey guys! Haven't been here in a while (rl issues). Anyway, been driving truck like an old lady all summer for good mileage (16.6!!!) and haven't messed with tuning or added parts etc since early spring. Anyway, last week all of a sudden truck developed a bad surge at idle. Doesn't do it in gear at idle, only in park or neutral.
Any idea what parameters I should log, and what I should look for?
Thanks!
Chris

 

[LarryJewell]

moved here

 

[Alligator]

Fuel Pressure Regulator going bad.

 

[sweetdiesel]

IMO the best thing to log is the RP current


I would try some 2 stroke oil first

 

[Skyhigh4by]

X2 As soon as I notice surge I dump some 2 stroke oil in the fuel and it clears up. Happens maybe every 3 months...

 

[dmaxtruck]

Bad news

Well, i didn't get a chance to log the damn thing this past week (muzzleloader season!). So yesterday I was going down the road and she started surging BAD as I was going down the driveway. RPMs alternated way up and down with my foot off the throttle, then she stalled out. I pulled over and tried to start it up to limp back, and she won't do it. She turns and turns and turns, but just won't fire.

I talked to a couple guys and they said it could be a check valve gone bad or clogged in the return line underneath the fuel filter. Basically acting like a cut off switch in a tractor. I'm going to check that tonight... anything else I should look at as a likely suspect?

Thanks again,
Chris

 

[dmaxtruck]

Update: took off the fuel filter and turned the key and the fuel was coming out fine. Cut the filter in half and the filter was greyish, but not bad enough that it needed to be changed.

Alligator thank you for the feedback, at this point it looks like you're right on with the regulator suggestion. I'll keep updating this thread till she's fixed. Going to get some quotes from a couple mechanics to see what it would cost vs DIY job. Fun stuff.

 

[kws808]

Alligator is right it sounds like a bad fuel pressure regulator. Did it throw any codes? Also if you can log your rail pressure it would help everyone diagnose it better.

 

[dmaxtruck]

I can't start her up and log because she won't fire. It just cranks and turns, but no fire. Never got a chance to log or scan the old girl before she quit on me, it was black powder deer season...

 

[JoshH]

Log rail pressure and regulator current while it's cranking.

 

[Jared Duramax]

is there any way to bench test the regulators?

 

[05smoker]

is there any way to bench test the regulators?

Tap it against the palm of your hand and see if the plunger still moves. That's my bench test.

 

[dmaxtruck]

Update: I decided to take it to the dealership because I was headed to Montana for an elk hunt (oh yeah, and I got a big bull too baby!!!) and I wanted it fixed before I got back.

So they checked everything and it ended up being my fuel pump. Then they found that I had cracked the resistor ring on my crank shaft. The guy said he's never seen a diesel with a cracked resistor ring in his life WTF is that?

Anyway, he said GM is covering it all under my power train warranty so it won't cost me a dime! :rofl::hug::angel:

I can't believe they saw the guages in the cab, looked under the hood, and are still going to cover it!