Engine/Transmission (1998.5 - 2002) Engine cut out / stumble

[nascar]

I have a re-occurring problem from last year. It cleared up, and now has returned. The engine will cut out and stumble while driving. This happens at any speed, with or without cruise control. Mostly it happens during interstate driving. It gets bad enough that sometimes I can't keep 55mph speed. This isn't the dead pedal syndrome that I've read about. This can happen at any pedal position. The way you can duplicate this problem yourself to see what I'm talking about is - Drive on the interstate at a constant speed, then all of a sudden, take your foot completely off the accelerator. Then, after about 3 or 4 seconds, put your foot back on the pedal for a few seconds, then repeat. It's very aggravating. It goes on and on. It's not only interstate speeds. It's has done it at neighborhood speeds as well.
Here's where it's weird -- If I start out with a cold engine (parked overnight), I've driven 75 miles without any problem. Problem only happens when the truck has been running already for the day. Not thinking it's the cam position sensor because tach works fine. I really don't believe it is anything mechanically wrong with the VP44. If it was, it should do it any time. It has something to do with heat I think. Although, that doesn't explain why I can drive it for over an hour without it acting up (as long as I start out cold in the morning). It only does it with a load on the engine too. I can press clutch and engine will hold a constant RPM.
I've searched forums for answers. Best answer I've found is it may have something to do with the VP44's electronics.
I will gladly replace the VP44, but I want to be 100% sure. Last thing I want to do is replace a injection pump and the problem still exists. I have replaced the MAP sensor already. That was $100 wasted!

Help!!

 

[JR]

What about any engine codes? Do you have a programmer of any sort?

A faulty APPS will give similar results as you are describing but is usually accompanied by a CEL.

 

[nascar]

I have used a Snap-On diagnostic scanner tool model MT-2500. It showed no codes anytime at all.
Fuel pressure is fine too. APPS voltage rises and falls at a steady pace throughout accelerator pedal range.

 

[klcammie]

Did you check connections to cam sensor? Also check the connection to the vp44. mine was loose and did same. Also check all grounds.

 

[nascar]

Connections are good. Found a loose body ground strap back under the front of the bed several weeks ago. Tighten it, but it made no difference.

 

[klcammie]

Have you checked Blue Chip Diesel. They have some very good instructions on how to check the vp 44.

 

[nascar]

I'm looking for someone that's had the same experience as my problem. What did you find out was the cause? What fixed the problem? I'm sure I'm not the only one who has had this problem before. This had to have happened to somebody out there before.

Anyone???

 

[JR]

Your issue has to be either APPS, VP44 PSG or ecm related. Makes it very difficult to diagnose when your not throwing any CEL. I know personally I would try recalibrating my APPS or even replacing it before I went for the other 2. Worst case scenario you have a spare APPS to throw in your glove box for a back up. Do you know anybody with a VP44 powered truck that you could swap ecm's with? You could eliminate the possiblility by doing a quick swap.
If your batteries have some age to them it may be a good idea to have them load tested also. Improper voltage will make the system go haywire.
Hopefully someone else will chime in but with the limited info it's gonna be tough to help ya.

 

[Raptis]

Hey nascar, are you still looking for a solution to this issue? I've been having the same thing for a day or two. I think aftermarket fuel pumps are supplying too much psi to the high pressure injection pump VP44 (CP3 in mine). I think in an earlier post I saw that you have an aftermarket fuel pump. How is it routed? Straight to the VP44 high pressure injector pump?