My truck runs rough at idle, any throttle position, unloaded, under load, doesn't matter. Now it is NOT a cylinder misfire. However, it does seem to sound consistent when i enable 6 cylinder high idle. You can hear it and feel it in the truck during high idle (you can even see it in the mirrors. I have tried to take a video but it doesn't really show up well because the truck is just so loud. Now in 6 cylinder high idle (at 1200) rpms the "miss" is Consistent but about once every second or so. How can this be?! The whole fuel system seems to check out. Fuel pressure is all normal. Still have great fuel economy and power. There is usually a heavy lope when cold, then clears up when driving. If you listen to my truck from about 100 feet away, you can hear it running strange, like its not firing consistenly. When im cruising going 55 and let off the gas SLIGHTLY (so little load on engine), the truck starts sputtering and can be noticed on tach (+/- 50-100 rpm). And when coming to a stop (no throttle), it will sputter the same way until i get to a complete stop where you can hear the truck lope (SLIGHTLY) at idle. I have taken it to the dealer twice, cummins once, shown two other diesel mechanics...and they are stumped. The ONLY thing I can think of is a new harmonic damper. I ordered an ati damper to see if it helps. I hate to throw a part at it but Im at a loss. If anyone has anything I can work with please help me. I can't drive it till i get this thing fixed. Ill try to get SOMETHING for a video but...

Has it been said in this thread that a broken ring can cause a rough running condition.....?

The pump can fail with out a code. It is very unusual however from what I have read. You did do the hot wire test and it seemed to work. That test is suppose to eliminate the pump as the issue.

  I going back to something that @JAG1pointed out. The volt meter was reading pretty normal in the first video but looked out wack in the second one almost like the grids were running. Your coolant temp looked high enough for them not to be. How does the voltage look with everything hooked normally and warm? Low voltage will make these trucks do weird things.

5 hours ago, KATOOM said:

Has it been said in this thread that a broken ring can cause a rough running condition.....?

The rough running is only at idle Katoom.

 

I think like Dripley said something is causing an electrical load drawing down voltages across some of the sensors causing a rough running idle. All I can do is cast my vote is all on this one.

 

Make sure tho that your lift pump runs off the batteries. If the excessive load is caused by the lift pump, happens from time to time, you wont be slowly burning up the ECM.

Edited December 19, 20168 yr by JAG1

Good call JAG.  Hard to keep track of whats going on when threads last so long.....

I've known problems like this where you start jumping into all sorts of different solutions cause all you want is to help the guy ....I know

 

Then on my truck I'll be thinking all sorts of things trying everything to fix it.

Edited December 19, 20168 yr by JAG1

The volt meter was low because my batteries were going bad. I picked up two new batteries. All is well in that area. but the problem still continues on. I have done the hot wire test when cold and hot and the problem still exists. My compression test seems to show i don't have a bad ring. I WILL NOT GIVE UP! im pretty stubborn.

I guess I am confused then. On page 2 you said that you redid the test and it ran fine hot wired. Did I miss something between then and now?

That raises question for me too.....

Thats my fault the first time in the videos when it was hot wired, it was already pretty warmed up. It was BETTER but not 100%. This time i let it sit over night and hot wired it first thing in the morning, ran like garbage and much more noticeable than when warmed up. Whatever it is, its hot and cold is my point. Sorry for the confusion. 

I think this is something electrical. Everything mechanical is checking out. Compression good, injectors new are good (even my old ones are good), new o-rings on connecting tubes, no air in system (using clear hose method), lift pump has good psi and connected to batteries (and using relay), sensors are all working, no codes.

If your problem is occurring with the VP44 hot wired I would put my money on your IP being bad.  With it hot wired, you have taken everything else out of the equation.  The ECM is not feeding the IP information for it to run in this state.  If it ran fine with your pump hot wired I would look at something electrical or sensor related outside of the VP44.

 

That is just my two cents, I'd look at changing that.

Or the VP is simply out of "timing" because of the key cog.  And if the key is smashed in the fuel timing retard position then it cant advance enough during cold weather.

Did this start after the VP install? If so might it be possible that you installed the wrong key? They are different from pump to pump.

The key came with the new pump..

I feel your pain on this problem, my truck is giving me the same type of trouble,only worse. I really think the pump hot wire test is only good for showing mechanical soundness at idle. With the ecm unhooked, you can't throttle up the motor to check for any type of misfire. What if there is some type of intermittent signal going to your VP 44 when it is hooked up. There is no way to test for this as far as I know. I was even thinking about making a connector to go between the VP connector an the VP to check for corresponding voltage changes in any of those connections.

On 10/29/2016 at 8:17 PM, TFaoro said:

Mine does this in high idle, part throttle revved up, etc. It only does it with no load though. Through different VP's, injectors, programmers, an entire engine, etc it has always done it. I chalk it up to an angry injection system and live with it. 

This explains my vibration I felt on 3 cal high idle the other day.