intermittent rough idle

[DaveNY]

After a run at Highway speed I stop at the bottom of off ramp and engine has a little jump in it for about 30 sec and then smooths out. has always been there but not every time.Seems a fellow 6.5 owner has same glitch on occasion. I am curious if this is common.I am not overly concerned as the truck always recovers and runs very well the past 7-8 years.
Dave

[More Power]

It could be due to a lot of different things... For any engine running problem, always begin the process of troubleshooting by changing the fuel filter and checking the lift pump fuel pressure.

Then, theck the condition of the injection system related wiring and the various sensor wiring, looking for chafed insulation, fully seat electrical connectors, etc.

Check the condition of the timing chain (easy to do). Too much slack could produce engine roughness at specific engine speeds that comes and goes.

The last item to replace is the fuel injection pump - though it remains a possibility... ;)

Jim

[DaveNY]

Thanks for the feedback Jim. At 160,000 mi I lean towards injectors or a related problem.I posted because I started to hear a few people I know have experieced the same phenomenom and just sort of seeing if others have seen the same.
Dave

[Robyn]

Three things that come to mind that can contribute to an unstable Idle after long periods of sustained speeds as the crank sensor and the optical sensor.

The last item is the remote possibility of a small amount of air entering the system and after a run down on a closed throttle could distrupt what the Optical sensor is seeing and or effect the case pressure in the IP.

These electronic injection systems can and do develop quirks.

To rule out a air issue, install a clear tube on the return from the IP to the hard line that heads back to the tank.

This can be done right up on top without too much issue.

Run the rig and then do the down ramp thing, pull over quick, pop the hood and observe the fuel in the clear tube. If you see bubbles streaming therein lies the issue.

As Jim mentioned, be sure the filter and the lift pump are in good order.

Another thing, (Just a thought) if the truck is a 94-95 and has a filter harness that connects to the optical sensor, replace it.


Battery grounds, PMD harness ground (must be to the IP and not to a remote cooler)

Remote mounted DTECH PMD is good too.


Make sure the return flow to the tank is unobstructed. Too much back pressure can drive the thing whacky.

A coolant temp sensor can cause a ragged idle if its going south.
Have you ever had any codes (SES LIGHT ON) pop up after the wierd idle ??


Keep us posted


Missy

[DaveNY]

Robyn,
I have long felt this is an injector problem or fuel related. I have a suspicion that it is indeed some air in the system.(similar problem on boat 3208 with leaking primer pump draining fuel and introducing air allowing same jump as in truck,just as lazy to fix this as to go crazy on the truck) I have checked all grounds,lift pump,and filter change, everything is ok. No codes.
A while back I posted about how my truck noticably runs better after topping off the tank.It makes me wonder if I have a small crack or hole in P/U in tank? Allowing a small amount of air into the system.I will have to check the return and see whats up.

Dave

PS. Hope you are well,Not been on in along time