Engine/Transmission (1998.5 - 2002) Bad surge when off the throttle

[Qualey]

My 02 HO/6 speed has developed a nasty surge when coasting in gear without a load on the motor. Hit the gas and it goes away. No low fuel pressure, no codes, filter changes seem to make no difference. Took the Edge Comp out to get reflashed thinking it was the issue, no change. Truck is currently stock except for 275, and 4" exhaust turbo back. 128k for mileage. I hear a lot of talk about the new fuel, but don't know if its a red herring or any way to isolate it even if I could. I have heard of guys with this same motor complaining about the fuel attacking injector seals , and this does feel like air in the system, but don't know. FWIW, its also got a heck of a vacuum pump leak.



The Cummins shop can't look at it until the 26th, so hopefully somebody's got an idea I can examine?

 

[ThrottleJockey]

Define 'surge'. Be more specific. A LOT more.



See, technically, 'SURGE' is impossible with your foot 'OFF' the fuel pedal.



But I think you mean something else.

 

[Qualey]

True; the surge is there under part throttle application such as holding a steady sped on flat ground in any gear. Increasing the throttle makes the symptom go away and does not decrease fuel pressure dangerously.



To add insult to injury I did read a P1693 code today. Been down this road before.

 

[cojhl2]

Define 'surge'. Be more specific. A LOT more.



See, technically, 'SURGE' is impossible with your foot 'OFF' the fuel pedal.



But I think you mean something else.

Drove a Pete/cummins a few years back, that as you were reducing the accel to make a shift that engine would take off!! I blamed it on the turbocharger for a while. But it got/was so disgusting we finally took it in.



They found some issue involving a connection between boost pressure and the pump. I dont know zackly what it was but it sure fixed the surge when releasing foot off the pedal!

 

[ThrottleJockey]

That's the famous 'APPS' surge. Adjust the APPS and CLEAN the IAT sensor and MAP sensor.

 

[GiesJ]

I have this same problem but the surge is more the throttle has a mind of its own. It will jump up to 3200 rpm, give me a dead pedal and then run good.



Only thing I can tie it to is the dash temp gauge dies at the same time the throttle gets possessed. Swapped my buddy's APPS (or TPS whatever the heck it is called) and was able to reproduce the probelm.

Funny thing is I have a P0123 code (TPS circuit high input).



Any insight greatly appreciated (https://www.turbodieselregister.com...-1998-5-2002/191227-tps-throttle-bucking.html)

 

[2-ND TIME]

Bad surge when off the throttle!

Ok first thing to do is to have the dollarshops use the DRB as a scanner (I don't remember what the name for it is that they use)for the voltages on the apps wires and on the bolt of the PDC. These things sound like mine since new! Mine is at 1100 to 1275 rpm, worse, undriveable below 1400. I am willing to bet a hundred dollars that if you use an oscilloscope you will find that there are very bad voltages on the signals. They don't come from the batteries, alternator, or ECM!!! The lift pump could be the source for the problem ( the circuits that limit the voltage to the pump in the reduced pressure to start. What I figure that the circuits are staying on and not turning off. ) Someone should find away to disconnect it. ( If it is in the ECM replacing it didn't fix this problem. Their is a capacitor ( maybe ) in the pcm that goes bad (mine was since the truck was new) and doesn't absorb the spikes enough to give proper fueling .



When yours goes to surging does the throttle responce make the engine rev but give little power on acceleration?