Hey all, my apps is dying on my 02 2500 diesel. P0121 and dead pedal occasionally. Timbos website says if my truck has the bellcrank assembly his apps will fit. I'm away from my truck for a couple of days and can't remember if mine has it but don't ALL 24v cummins have it? Are there 2 different apps styles? I don't want to order one if its the wrong one...oh yeah, mines an auto tranny too.
Thanks.

 

Not sure if there are 2 different APPS sensors. I've never had to touch mine.

When you get dead pedal, does the engine respond if you push the throttle down more or less (like there's a dead spot in the sensor), or does the engine not respond at all to any throttle setting?

A dead spot in the APPS indicates that the APPS is going bad. A dead spot in a potentiometer does happen. But if the whole thing is unresponsive, that indicates that you may have deeper issues such as a loose connection, ECM or FPCM (computer on the VP44) issues.

Take a look here on thye VP44 diagnostic page over at Blue Chip diesel. He's got a good read on the VP44, it's problems, and a whole section on dead pedal issues.

http://www.bluechipdiesel.com/vp44diagnostichelp.html

 

Thanks, it seems unresponsive over the whole pedal momentarily, engine doesn't die, but when running hunts for lockup around 50mph and code P0121. From what I've read, typical apps fail. I'll look at the link you sent, hate for it to be PCM

 

The transmission hunting is a separate issue, easiest fix for that is cleaning all of the grounds.


https://www.dieseltruckresource.com/...52&postcount=6


The PCM (Powertrain Control Module) controls the auto transmission, and is located on the passengerside firewall. The PCM does not have too much involvement with running the engine. The Cummins ECM (Engine Control Module) and VP44 FPCM do that.

The FPCM (Fuel Pump Control Module) is the small computer attached to the VP44 injection pump itself. It directly controls the injection pump and communicates with the ECM, and together they are primarily responsible for running the engine.

Take a look through all of the links, especially the one from my earlier post. That link has an entire section on dead pedal, and it is not always the APPS.

Hope this gets your truck running better.

 

Hi Jrs Dodge Diesel, thanks for your input!! I did read the other links and one of the causes, although rare it seems, is a bad fuel system relay. Just to test it out I swapped the fuel system relay with my horn relay (hardly ever use horn) just to see. I didn't get dead pedal yesterday or today driving home and to work (30km each way, varying traffic). I doubt this is it but it was something to try.
One strange thing though, when I left for home last night I had my check engine light on because I'd thrown another P0121 code. I have a code reader but I never cleared the code, figuring I'd leave it until I got an APPS. It was still on after the relay change out last night. This morning on the way to work the check engine light was not on. I did not clear it with my code reader. I didn't think codes/lights cleared themselves...is this normal?

 

Usually the codes will clear after a certain number of starts....but I think it is quite a few.

I guess a bad relay could cause the problems you mention. Does your horn work normally??

 

Usually a code has to be "active" to for the light to be lit. Like Kurt said above, some codes will clear after a few starts as long as they are not active. The code will still be stored in the memory until cleared by a scan tool or disconnecting the batteries for a while. I'll look in the service manual later to find out more on this.

For the relays, like any other mechanical device, they can and do wear out. The contacts that make the electrical connection usually wear out first. They get pitted and burnt from making and breaking electrical connections due to arcing. Relays that switch higher voltages are more prone to this, but it does happen to 12 Volt stuff too. You'll eventually get poor/intermittant connections which causes issues to whatever is connected downstream from the relay.

 

Thanks again, the horn did work but I only just tapped it a couple of times...a failing relay may or may not show up in that case. I did the key on/off test after work yesterday and the 1693 companion code showed up so I put my code reader on it when I got home and it told me NO codes had been stored so again, the P0121 that was there had cleared on it's own. I erased the 1693 with my reader and that's where it stands now. No dead pedal yesterday afternoon or this morning either. I'll keep watching and this weekend when I have more time I'll be scouring all the ground connections as well. Would love for this issue to have been just a bad relay.
Thanks again for all the great info everyone...I'll follow up as well if the condition comes back or stays gone, too.

 

Update: Well this morning I finally had a chance to clean all the grounds as per Jrs dodge diesel. What a difference! Feels like driving a new truck, no hunting whatsoever. So my issues at this point seem to have been a bad fuel relay and dirty grounds. Thanks again to Jr and everyone for contributing. Saved me a lot of headache and money!
Cheers...

 

Glad to hear everything worked out for you!

 

Nice! Great news!

Rock on brother Mamm.