Slight Hesitation after new pump and pmd

[BrentN]

Picked up my Suburban on Friday. New pump and pmd under warranty, plus they washed it too while I waited. Something of interest, they added a lubricant to the tank. Apparently this is something that they do with new pumps due to the low sulfur fuel. Probably to help with break-in of the pump.

Question for the group:
The suburban now seems to have a bit of a hesitation, almost like a light stumbling as you take off from a stop. Nothing major, but I do notice it. It clears itself very quickly and then seems to perform fine after that. It occurs when you first tip into the throttle. This is not something that was occurring before the truck went in for a new pump.

I am wondering if this is a timing issue and that I need to run it back and have them take a peek? Thoughts on this?

[Hubert]

At least go back and have them put the complaint in the records ASAP. IMHO its best to get a copy and keep written records of service (and complaints etc) especially at a dealer. So when service managers change you'll have documentation and it won't be a story arguing with them later.

I have sometimes felt a sublte difference in my truck from certain additives. Maybe its imagined but I think the viscosity of the fuel can change depending on the concetration or blend of diesel and additives. Then the electronic pump has a hard time metering it as precisely. Especially at light throttle and load.

So go back and get the complaint logged (maybe they'll adjust something too) then run the tank out and try straight good quality (high volume truck stop) diesel and see if there is a difference. Then do what ever you do on additives normally - many many opinions there.

I think the system will purge air on its own and settle down from normal use.

[BrentN]

Hubert,
Thanks for the input. I am going to give the dealer a call and have him make a note of it. I am trying to run this tank down a few more days before I hit the hi volume truck stop and refuel.

Since the day before the truck stalled on my wife, I had filled up at a non-truck stop, non name brand fuel...so just trying to rule out the fuel as being a culprit.

Then I will put some Power Service in it too and see how she does.

I and my wife have noticed that it seems quieter than before, so, I am wondering if the timing is a little off. That is the question I will pose to the dealer.

Thanks again.

[BrentN]

A little more info about the hesitation problem my burb is experiencing.

If I bring the RPM up to ~1000 rpm you can definately feel what can only be described as a zone of rough running. At idle it runs smooth and everywhere else except for right around 1000. As soon a little more throttle is put to it the engine smooths right out.

I am calling the dealer this morning, but was hoping to have something to steer the tech with.

[BrentN]

Interesting update:
Called the dealer yesterday morning to let him know that the truck is not running so well, he cant get it in until tuesday after Memorial Day-the diesel mechanic is on vacation.-Kinda a bummer as we are taking a road trip this weekend.

Late yesterday afternoon, my wife called, Check Engine Light came on. Took to Autozone, PO251.

I am sitting in their parking lot thinking..Its going to be a long weekend and given the symptoms, I suspect the pump timing isnt right. So, went ahead and did a key on-key off-key on APP to the floor for 45 secs. Let off, restarted, Check Engine Light gone, but more importantly, the 1000rpm shudder was gone too! Have driven 75 miles and absolutely no problems with the tip in throttle problem.

From what I have gleaned from this group is the dealer doesnt necessarily perform a TDC offset learn when a pump is replaced. What I also read, somewhere here is that that performing key off-key on procedure, forces that TDC offset learn.

I am still pretty new to this engine and how everything works, but I do know that my burb is running great now!

This weekends roadtrip will prove that out I guess.

Brent

[ 05-26-2005, 08:31 AM: Message edited by: BrentN ]

[jan5]

Had exactly the same problem with new pump from gm.The dealer told me to run it.One added problem was a slight stumble when the converter locked up also. (very slight) Long story made short got a 251 at 4000 mi classic pump stuff. Going head to head with dealer now for warranty, they say bad fuel I say bad pump. they dont want to make good.1999 GMC suburban 2500 410 103000 mi.