Engine/Transmission (1998.5 - 2002) rough idle questions

[The Red Goat]

here it is



I am getting a rough idle after the engine warms up. I see where people are calling a miss, but with my truck it seems more like a hiccup. The RPM seem to go up. Other than this truck is running fine.



Thanks for the help.



Curtis

 

[Tcolesanti]

What's your lift pump pressure at idle? At Wot? Maybe its a problem with the fuel pickup in the fuel tank? (clogged, etc. )

 

[Bob4x4]

Two most common reasons for rough idle I see are vp-44 and valve adjust.



Bob

 

[Guest]

Should have felt and heard the idle on my 02 when I smoked the VP, was like a big cammed dragster w/ no power... ...

 

[The Red Goat]

fuel pressures are fine. A valve adjustment may be in order. the truck has 131,000 on it now. The truck has all the power I can ever use right now. I hope it is not the pump.

 

[The Red Goat]

the miss hiccup or stumble is not noticable with a little bit of throttle say 950 rpm. It is also very erratic

 

[nuv22]

Mine is also very erratic and it does it also after it is warm, and I turn the truck off and back on within like 2 minutes and idle. After I drive off problem is gone

 

[The Red Goat]

I used a little injector cleaner (a 50-50 mix of lucus and Power Service at 2oz/3gal desiel) in mine and the problem fixed itself. May have been a bad fuel, maybe the pump is going.

 

[lmills]

did anything ever come of this? I have a friend that is experiencing the same thing that the Red Goat is describing. He has plenty of fuel pressure. Somewhere around 30 psi of liftpump pressure. The idle is very irratic and choppy. Off idle the engine runs great. Any ideas?

 

[SnoKing]

30 PSi is too much fuel pressure! More is not better. SNOKING

 

[lmills]

why do you say that? everybody I have ever talked to said that high fuel pressures just made the 24v trucks hard to start. They never said anything about idle problems. he is running the same set up a lot of people run. It's a holley blue pump pushing through the factory lift pump. I personally thought the pressures was high for the set up he was using.

 

[The Red Goat]

Nothing has ever come of the problem. The truck still does it from time to time, I just add special sauce to mine and it seems to quit.

 

[gonehuntingagain]

Should have felt and heard the idle on my 02 when I smoked the VP, was like a big cammed dragster w/ no power... ...

My VP-44 did the same thing, although I still had power. At first it only did it when cold and didn't do it all of the time. Just as I was about to take it in to get looked at it quit doing it. A year later it started again, this time it would do it when the truck was warm and was getting worse. Took it in to the dealer and the tech tested the lift pump (was ok) then unhooked the VP from the wire harness and plugged the Cummins tester into it (isolates the VP from all other sensors) - still had the problem. The dealer replaced the VP-44 under warranty (only had 85,000 miles).

 

[Silver Bullet Ram]

My truck does the same thing, I added a bunch of fuel additive it has seem to quit doing it. I had a injector pump replaced last fall, has done it since the replacement. I have wondered since the pump gets starved after a lift pump failure if all this is bad for the injectors too?



Gary

 

[Texas Diesel]

I've got the same problem but only when hot. A valve adjustment didnt help any.

 

[Oil Burner]

I've got the same problem only when hot.



swapping injectors didn't make too much of a difference.



Jason

 

[Silver Bullet Ram]

Beginning to sound like bad injector pumps. Thing is mine is new and the dealer said nothing is wrong with it.



Gary

 

[2-ND TIME]

bad idle

sounds like mine. Worst piece of junk I have ever run. I have been told that will have to get use to it. It misses the worst at 1000 to 1275 rpm and the fueling starts above 1400+ Can't run it below 1700 or 1800. Mine is bad voltage out of the PDC for the alternator and batteries tested good according to the o-scope. This screws up the voltage to the vp with the embeded info and it's other cct's. Still trying to figure out how to get the scanned pages on to the or screen.

 

[Silver Bullet Ram]

What is a PDC? and CCT?



Gary