Hi guys,

 

i have a 2003 cummins auto trans that I am having dead pedal issues. No codes. While driving at completely random

times the truck will completely drop off to idle for a couple seconds, then come back to the desired rpm and work fine. Sometimes this happens very rapidly and makes the truck undriveable. On the rare occasion that the truck does not act up it runs perfectly fine with plenty of power.

 

I replaced the APPS and it made no difference. Checked continuity on harness from each of the 6 wires from the apps to the ecu connector, all OK, checked continuity from ecu connector to FCA and found OK, checked continuity from

each pin in the ecu connector to all other pins and ground, found OK aswell.

 

I have a good 5v signal voltage to the APPS and checked resistance on return side of circuit from APPS connector to battery ground with the key off and found 1 ohm. Signal voltage from APPS to ECU checks out OK as APPS cycles through its range of travel, even when the pedal goes dead. 

 

While monitoring absolute throttle position % with scan tool, throttle position reads fine, even when the pedal goes dead.

 

I also removed the FCA and cleaned it with wd40 and reinstalled.

 

I am thinking there may be an ecm issue but I'm am not sure of any other testing I can do to make an accurate diagnosis, I've been trying to get my hands on a known good ecm locally but I can't seem to find one. Any suggestions on where to go next?

I only know enough to do light mechanical but is it possible your problem could be fuel related? i.e. bad tank vent causing starvation, clogged tank screens?

 

Another thought is bad engine ground any other grounds? PCM ground or injection pump connectors?

 

Just tossing thoughts.

I really don't think it's fuel related but it is possible. It has loads of power and is not

smoking, doesn't sound like it's starving for fuel. It pulls great and just falls right to idle at the snap of a finger. 

 

I'm going to try and piece together a gauge to measure my fuel

pressure today but I don't think I will find an issue there.

 

i will check the grounds aswell.

Edited April 5, 20178 yr by Tslaney

Based on your description is sounds more like a trans issue than a pedal issue. 

 

If it were a pedal issue you would see the scanner show the TPS changing. 

 

If the rpms are dropping to idle while you are in gear and moving the issue isn't with the TPS or engine, but in the trans. 

What component in the trans could cause this issue? And what tests can I do diagnose that component? It happens in park and neutral aswell.

So what happens when it's in P/N?

 

Nothing in the engine should cause the rpms to drop to idle while in gear. 

A had a friend with a 2006 Dodge that just got done with this issue and it happen to be excessive AC noise from the alternator. I'm not exactly sure of the limits for the 3rd gen truck you could try my home test and see if it works for you.

My buddy replaced the APPS sensor as well and didn't resolve the issue. It would randomly drop to idle and leave without power. After replacing the alternator which in his case completely failed and stopped charging altogether the dead pedal issue went away. 

How does AC noise cause it to drop to idle in gear?

Basically, in a nutshell, AC noise from the alternator will muddy the signals within the ECM. So anytime the ECM sees a signal out of range it drops to idle state disregarding the commanded throttle. My buddy 2006 Dodge we changed the APPS sensor and still had a dead pedal issue. Once his alternator gave up and was replaced the problem went away. No longer having dead pedal.

So it messes with the trans too, and causes it do shift into N? 

 

Doesn't seem that an engine issue should allow rpms to drop to idle while in gear, but stranger things have happened. 

 

 

Edited April 10, 20178 yr by AH64ID

1 hour ago, AH64ID said:

and causes it do shift into N? 

 

That's a hydraulic issue. 

 

The only thing the ECM/PCM can do is cut fueling. It can't shift gears that all in the valve body. The most I can think off is that if it cut to idle state that it feels like its in neutral because its just free rolling. (Educated guess).

Idle is an rpm, not a fuel value.... so is it dropping to idle or 0% fuel? 

 

Zero fuel in gear is not idle. 

 

 

Edited April 10, 20178 yr by AH64ID

3 hours ago, AH64ID said:

so is it dropping to idle or 0% fuel? 

Idle. So if it not rolling it's idle. If it's rolling it 0% fuel because RPM is above idle fueling so fueling is cut.

 

@Tslaney So I'm wondering what the OP has for feedback...

Okay... that makes a big difference in diagnosing.