Strange Reving problem

[lmholmes11]

Hello All,

I have a 2001 Chevrolet Silverado 2500HD Turbo Diesel. Whenever it is idleing i can hear the engine reving a little bit by its self. Its only 100-200 rpm's but it is noticable. Anyone have any suggestions? Thanks!

[Mark Rinker]

Most likely caused by a failing fuel pressure regulator. My 2002 has done this for the last 100K miles, and I have repeatedly decided to leave it as-is due to the high cost of repairing it. I have been quoted $600+ part and labor, I'm sure someone can chime in here with the do-it-yourself cost...

[More Power]

Mark has it right.... It's likely the FPR, in that it can't regulate fuel pressure in the high-pressure common-rail quite like the ECM thinks it should - though not bad enough to set a trouble code. Like Mark's truck, my 2001 has done this for a couple of years now, but was made less prevalent by using a fuel treatment (at least it appears so) that includes added fuel lubricity. I use either Stanadyne Performance Formula or Power Service.

Back a few years ago, GM chose a 100-rpm variability at idle as the limit requiring corrective action under warranty. The FPR can be changed without removing the high-pressure pump - though a bunch of stuff would need to be first removed to get to it. A search here in this forum would likely turn up a bunch of discussion about this issue.

Jim

[lmholmes11]

ok thanks guys, i also read that it could be the fuel filter, so ill change that and see what happens, thanks!

[Duramaster]

Last time I checked the price of the regulator alone it was around $300 +/- $50. The labor is around 3.8 hours I do believe. But with the right tools I have replaced them in under an hour!! :cool:

[Duramaster]

I might also add that there is updated software for the 2001 DMAX that addresses idle surge, but it rarely actually fixed the idle surge. :)

[lmholmes11]

ok thanks for the info. Will it hurt anything if I let it go for a while?

[lmholmes11]

also, is there a chance changing the fuel filter help at all?

[Rick Henderson]

My 2003 does the same thing and did it before I had the injectors replaced. After the injectors were replaced, it went away. Now the surging as I call it is back and diagnostics show 6 and 8 injectors are bad and need replacing.

Is this the same thing?

[More Power]

ok thanks for the info. Will it hurt anything if I let it go for a while?

As long as no codes are being set and you can cope with the surge, it'll not likely hurt anything to run it. I would try some fuel treatment that includes additional fuel lubricity for a few tanks of fuel to see if it helps.

Jim

[OC_DMAX]

I agree with the above comment about running the additive. My truck has always had a swing in the idle speed that is noticeable. If I run an additive, it settles out. May want to give it a try.

[crafty]

In the last few weeks my truck has started to do the variable idle thing too. I was going to ask the same questions as asked above but I think I will let things go for a while and see what happens.
I now have 155,000 KMS on the truck and I still have 3 original injectors.
Is there a chance that the idle is being caused by a bad one or would it most llikely be the FPR? As stated the change in idle is only enough to hear it but not enough to move the tach.

[More Power]

I now have 155,000 KMS on the truck and I still have 3 original injectors.
Is there a chance that the idle is being caused by a bad one or would it most llikely be the FPR? As stated the change in idle is only enough to hear it but not enough to move the tach.

It's most likely the FPR. A leaky injector usually produces a fuel-rail pressure code. Otherwise, the system will compensate within limits for an out of balance injector. As OC and others have suggested, try some commercial fuel treatment that includes additional lubricity and cleaner. ;)

Jim

[Kennedy]

also, is there a chance changing the fuel filter help at all?

I would definitely change it or at least verify the restriction present.


ok thanks for the info. Will it hurt anything if I let it go for a while?

Just be careful maneuvering in tight areas. This surging can affect the smooth operation of the vehicle if bad enough. I had a Customer (SOMNDMAX) who had this issue. His did not meet GM's criteria for warranty so he dosed it very heavily with FPPF Total Power and it subsided for a quite a while. Eventually it came back. When it came back he stopped treatment for a tank and it became bad enough to get warranty coverage.

[Mark Rinker]

My 2002 has intermittantly surged slightly for so long, that its almost a 'signal' as when we need to change the fuel filter and run more fuel additive...

What is the correlation with additive? Lubricity?

[lmholmes11]

Thanks for the info guys, I changed the fuel filter and its running just like new again!