dunterberger

I have one I need help with. My Sons 2500 series Auto/2WD) has a very weird accelerator pedal (in park or in gear) . It starts and idles just fine but as soon as you move the pedal thr Engine revs up turbo boosts and then it fall back to an lower rpm and if you hold the pedal in that same position or depress it further is continues that cycle of racing up and falling on it's face.

I checked and cleaned the cables and grounds at the fenders and block for both the ECM and battery grounds I did a voltage drop as well on both the Positive and negative cables and installed 2 new batteries as they were bad. I tried to check the APPS and its inputs/outputs but the wire colors don't match up to what I have. I put in a new APPS from Oriley's Auto Because of a (P0221 and symptoms) and did a reset on the APPS I thought it was fixed as it worked fine for about 2 miles and then the issue returned.

I took it to be checked out at a place near me that supposedly specializes in Diesel truck and they basically said we will try to fins a good used ECM and see if that cures it.

I am not typically a parts changer. I would like your in put or at least a logical test path to follow.

Could I have fried the new APPS? Is my ECM bad? Has any seem thids before?????

dkenny

what year truck?
in my 99 I never see boost by reving the engine..
to check the apps..leave the truck not running but with the key on..
find the output wire..connect an analog volt meter(it'll work better than a digital one). press the pedal. watch the output..should rise smoothly to about 5v..
when my ecm went out..I was having the 'wait to start' light flash...and it was very hard to start but ran fine after it started..

just my cents
-dkenny

dunterberger

Thanks for the input. I was using a digital meter by habit, I'll grab the analog and see what it reads. Also your right .... in park it just revs and dies down no boost. but if your in drive and trying to take off it surges forward for a few seconds then fall on its face if you ease out of the pedal you can kinda a time it and get up to speed and maintain it by feathering the pedal.

If I end uo needind a APPS or ECM do you have ant thoughts??? I was looking at a TIMBO and as for the ECM I can get a re-manufactured one from Dodge for $453.00 + programing. As ther any ones that are better than the dealer, Can I use a newer year.. may be they would be better if they would work.

Busboy

Get the TIMBO you'll never look back.

KATOOM

Using a decent code reader, make sure there are no other codes indicating another problem.

If you know how to verify the APPS volts with a reader then that would help you understand if the potentiometer part is working correctly.

Lastly, its VERY critical that you understand whether or not the alternator is generating excessive AC voltage noise. If it is then depending on the level, that AC noise will interfere with other neighboring sensitive electronics, like the APPS, PSG, and transmission solenoid. So check that out before you doing anything or replace more parts. Easy to do with a basic voltage reader too.

dunterberger

Thanks for the information, I will be working on it on Saturday. I think I still remember how to check for Nuisance A/C voltage voltage drops with system load. I do have access to Snap-on MODIS or Ford NGS scanners. I will post on Saturday my findings.

dunterberger

OK, so I had a chance to look at a few things over the weekend. I rechecked the lift pump pressure and it is 9psi at idle and 6psi under load.

I checked the A/C voltage and it is .3v at idle and .9 at approximately 2000 I will be taking it apart over the holiday to bench check the diodes.

The APPS. test with (sensor connected) seemed to check out. The Voltage in Pin 5 is 4.9V / as were pin 2 & 6 (idle validation switches). Pin 3 Signal to ECM is at .55 and seems to increase and decrease smoothly with the pedal Does any body know what the Max output should be at Full throttle? I think I remember reading 3.8v.

The APPS grounds that are on pin 4, I think it is out of range. It reads 24K-ohm I think I remember reading on the Mitchel diagnostic test that it should be no greater than 5k-ohm... and if it is greater then check all the grounds and connections and if they check out... well its ECM time.

The last thing I will add is the truck seems to only have 2 speeds... IDLE and ACCELERATE... I heard someone the other day refer to it as (LIGHT SWITCH THROTTLE)... Has any one heard of this and is there any information out there on this symptom.

As always thanks for everyone's input... Have a great Thanksgiving!

KATOOM

Its advised to NOT attempt to adjust the APPS voltage, but nonetheless here's a tech article in reference to the voltage levels you should see. https://mopar1973man.com/cummins/art...djustment-r34/

dunterberger

Excellent article Thanks. Any thoughts on the trucks drive ability issue? it idles fine but as soon as you depress the pedal it accelerates you have to let off the pedal you can't cruise down the road without constantly being on and off the pedal... like turning a light on then off the on then off and so on...

KATOOM

That sounds like an APPS issue, but if you can confirm the voltage ramps appropriately throughout the throttle movement then.....

Busboy

You are either having an apps problem or you will in the future, the Timbo apps is far superior to the factory set up and I don't believe anyone that has switched to a Timbo has had apps problems again.

dunterberger

Thanks, My Timbo shows up today so over the holiday I will put it on and repait the alternator, my hope is all will be solved and I can then move on to installing the air dog fuel system near the tank where it should be... Have a great holiday everyone and thanks for the help. I will post what I find.

dunterberger

Well I am perplexed! I put on the Factory rebuilt Alternator and my A/C voltage issue went away it .ow reads .017! U installed the Air Dog 100 and I now have awesome fuel pressure and volume.

I put in the Timbo and it registers .62 (idle) to 3.82 (WOT) it is a clean smooth transition on the scanner. Everything should be good one would think...
So I go to test drive is an it runs and feel like the old truck... for about a block and then I get a dead pedal This id something I never had the engine would not go over 1200 RPM. Well I got it back home and I just shook my head walked in the garage poped a cold one and called it a day.

KATOOM

After re-reading your posts, I kinda think you may be dealing with more than one thing. The strange lack of throttle/power when ramping the throttle in DRIVE sounds like the "torque management" is kicking in for the automatic transmission. Manuals dont have this intrusive feature.

The other complete lack of throttle response has me wondering if its related, but since you have a Snap-on MODIS scanner, cant you run this live whereby seeing what the APPS voltage is doing at that very moment?

dunterberger

Thank you for your response. Im not quite sure how I would diagnose the Torque Management issue if that is indeed what I have. Can you please elaborate a bit more about this. I think the ECM and PCM would have to be sending signals to each other and controlling the fpcm on the VP44 during acceleration and shifting. However, I am not sure what I would monitor on my scan tool or what wires I would check for signals. Maybe you know of a post somewhere. Thanks in advance for any ideas

(The otherday I was looking for my TCM as i thought is would be external on this vehicle but did not see it. Is it integrated into the PCM as I have heard?)