Engine/Transmission (1998.5 - 2002) rough idle problems

[Tomeygun]

is it normal to have a rough idle after truck warms up?



longer it sits at idle, rougher it gets



hmmmm.....

 

[rashwor]

It's not normal for it to sound rough...

but the tach may show it to be a little rough. It should not get worse the longer it sits. My tach bounces, but you can't tell it by listening to the sounds of the Cummins.

 

[andrewkoperdak]

You have a strange problem: the only thing that comes to my mind is that you intake heater is staying on. Watch you volt meter and see if it is around 14 volts or is it cycling at say 10 to 12 volts?

It is a stretch but that is what comes to my mind. Intake air too warm

 

[Tomeygun]

nope, voltage is fine, a little over 14 volts,

i notified the stealer and had service manager acknowledge the "miss" or rough idle symptom.

he said it could be the clutch has alot of material on it and is scuffing and causing the engine to try to hold idle perfect...



sounds like BS

 

[andrewkoperdak]

Clutch you say? Well you could rule that out by simply pushing the clutch in and out and check the idle for in and idle for out. If it is still rough then it isn't the clutch or somebody needs to teach me something new about clutches. Sounds like the dealer is reaching for straws.

Andy

 

[andrewkoperdak]

I forgot to add this. One evening I was very tired. While holding the brake on, I parked the truck and engage the parking brake fully. Somehow I managed to let out the clutch thinking I was on nuetral, I wasn't. The truck spun my tires all over the driveway holding idle all the while at 800 RPM. This only lasted about 3 quarters of a second but I noticed the RPM was at 800. I shut the key off to tame the beast. So what I am saying is the truck will idle fine even spinning the tires with the emergency brake fully engaged. Take that one to the dealer that says the clutch is thick and it might cause a rough idle problem.

I had a rough idle problem only once. The air temp was 111 degrees F and I had been driving about 6 hours without stopping. I pulled off the highway for fuel and she idled really rough. RPM swings of 300 RPM. I later found that my lift pump was questionable and my injection pump was probably overheating and causing my idle problem.

 

[Tomeygun]

Originally posted by AKoperdak

I had a rough idle problem only once. The air temp was 111 degrees F and I had been driving about 6 hours without stopping. I pulled off the highway for fuel and she idled really rough. RPM swings of 300 RPM. I later found that my lift pump was questionable and my injection pump was probably overheating and causing my idle problem.

how did you fix it?



i am hoping that my problem is not the dreaded lift pump/injection pump... would there be any other signs?

 

[andrewkoperdak]

If you have a fuel pressure gauge you can determine if it is a fuel delivery problem. You don't need to install one if you don't want to. You can buy one that you can use for testing purposes from you local autoparts store. I have both. Something to note though when checking fuel pressure. My engine would make great pressure until the engine got warmed up, say 20 minutes of driving. Then my lift pump would start heading south on me and eventually end up with 2 or so psi.

My rough idle I suspect came from my injection pump getting to hot due to the fact that my lift pump was bad. No cooling to the injection pump. I did not have gauges back then so I can only speculate. I have a relatively new lift pump and haven't had any rough idle since.

 

[Tomeygun]

UPDATE:



i borrowed one of the mechanic's fuel pressure guages and hooked it up for some serious WOT testing,





i couldn't believe my eyes when i COULD NOT move the needle off of 17 PSI, idle, wot, 1 psi difference at the most,



i don't think i hooked it up wrong, but i had no load at all, other than moving dead wieght of truck itself ...



hmmmm. rough idle still there though, darnit

 

[Vaughn MacKenzie]

Tomeygun, I've had a rough idle since my truck was new (had it 27 months and 66,900 miles now). I have a permanent gauge and have always had good fuel pressure. It idles considerably worse now than new.



I've had Piers and Lawrence at DD look at it and agree the idle is poor, it holds steady RPM but not all cylinders fire evenly and it is random. . . not any particular cylinder. Lawrence did a cylinder isolation test and all cylinders are even. He as well as a couple others are certain my injection pump is not healthy.



This week I bought dielectric paste and disconnected EVERY electrical connection underhood and added some paste and cleaned the connections, although they were all clean and most had sufficient paste. It made no difference.



When I'm done with my trips for the summer and can do without my truck for a week or so I'm going to take it in and attempt to get it replaced under warranty. There is a dealer about 40 miles away that I'm confident will honor the warranty and replace it. I'm hoping I won't lose any of the great power and good mileage I get when I get a new pump.



Vaughn

 

[Tomeygun]

what kind of mileage are you seeing right now?



(considering that your injection pump could be weak)



food for thought, a while back, an idiot employee here put gas into a HO/6-spd, and then it drove 5 miles and then died



towed it back, drained fuel tank, etc,

truck seems to be fine now... OTHER THAN ROUGH IDLE



LIKE MINE!!, I hope to hell that some idiot didn't put gas in mine before i got it and then fixed it before it was traded to the dealership i work at... i would never know...

 

[lsenus]

I remember reading somewhere that an injector had a cracked, or malformed, or otherwise screwed up tip on it that caused another member a similar problem. He had lots of smoke and running rich at idle. It could be something to have checked.

You said you had a cylinder isolation test done. Were the injectors pulled and inspected??



Food for thought...





https://www.turbodieselregister.com...page=15&highlight=injector crack&pagenumber=3