Intermittent dead pedal

[Mckelvey]

I’m no master diesel mech but a pretty decent all around mechanic. I’ve gone through all I know to check on this truck and can’t seam to find the cause of the issue. First of all, it’s a 99 auto, I have a smarty on it. New injection pump about a year ago from Industrial. Fass 95 system, holding around 14psi. I don’t think I have a fueling issue, I think it’s electrical. The truck will randomly lose throttle and drop to about half power. My APPS is only getting around .3** volts with it rotated as far forward (clockwise) as it will go. Any time I adjust the APPS I re-learn it. I tried the Timbo APPS and the issue persisted. I later learned that the 98-99 trucks don’t like the high voltage from the Timbo so I put the old sensor back on. I rebuilt my battery cables and cleaned ALL grounds I could find to bare metal (body, frame, pcm, etc.) I checked for bad diodes in my alternator, they’re good. I followed the black and blue ground wire from the pcm to Hell and back, couldn’t find any breaks, shorts, or corrosion. My batteries are brand new (interstate) I’m leaning towards and issue with the ECM. I could have possibly missed something or didn’t properly test something with the ground wire (black w/ blue tracer) but I just have a feeling it’s something in the ECM. Any help would be much appreciated!!

 

[Mckelvey]

Also, I disconnected the alternator to make sure it was excessive AC voltage and the issue was still there (actually got worse) I just pulled my codes with the smarty: p1693 (companion) and p0460 (fuel sending unit) my fuel gauge has been spotty lately so no surprise there. Also the ABS and brake light have been on since I bought the truck. I haven’t checked the schematics but aren’t ABS sensors AND the fuel level sending unit grounded through the ECM? Thanks in advance for any advice

 

[DavidC]

2WD or 4 WD ?. If 4 I would suspect a sensor problem on the front two. Usually on a 2 it is the sensor in the rear differential but that usually takes out the speedo also. I think blue chip has some good troubleshooting for the apps and fueling.
https://www.bluechipdiesel.com/

Dave

 

[Mckelvey]

2WD or 4 WD ?. If 4 I would suspect a sensor problem on the front two. Usually on a 2 it is the sensor in the rear differential but that usually takes out the speedo also. I think blue chip has some good troubleshooting for the apps and fueling.
https://www.bluechipdiesel.com/

Dave

Thanks for the reply
It’s 4wd, do you think the abs sensors could be causing the “dead pedal” issue?

 

[DavidC]

Thanks for the reply
It’s 4wd, do you think the abs sensors could be causing the “dead pedal” issue?

Not likely, that is a seperate issue. If you do not get the dead pedal check over at mopar1973man.com. There is a lot of info there also. Between these two sites I am sure that issue can be narrowed down.

Dave

 

[Road Dog]

I had a similar issue with my truck. It was the VP-44 going into limp mode. After a new TPS and injector pump it turns out a loose fuel connection at the tank allowed air bubbles into the injector pump. The bubbles affect the timing and generate an internal fault. Blue Chip discusses running a long piece of clear tubing across the windshield so a passenger can watch for air.

At least I have a new pump with the latest upgrades.

(The ABS-Brake lights indicate an ABS fault. It can be as simple as low brake fluid. The other common issue is the ABS sensor on the rear diff. It can be a bad sensor, bad connection, or the sensor needs to get loosened and pushed back into the housing. At some point the sensor was also used for the speedometer. If the speedo is erratic or doesn't work at low speeds then the sensor is suspect.)

 

[KATOOM]

Is there any rhyme or reason causing it or is it completely random?

First thing is to remove the smarty. Always remove any electronic devices when you suspect an electrical problem. If the problem remains then check the alternator AC voltage output. Excessive AC will cause all kinds of phantom issues. Being that you have an automatic, you may benefit from a voltage filter as well.

There's many things which can cause the ABS/brake light to remain on. Bad/worn/damaged sensor wires to the front hubs and bad brake light switch under the dash are a couple I can think of off the top of my head.

 

[Mckelvey]

Road Dog: I’ll look into that, I love for it to be something simple and cheap like a loose fuel line. Did your fuel pressure drop any with the air in the line?

Katoom: I does it the most at initial startup. The first mile or so it will either stay completely limp or jump back and forth from limp to normal. Also notice it more when I’m on the throttle (leaving a stop, getting on the interstate) the smarty came off and I test drove it, no change. I unhooked the alternator (pulled the small plug and removed main fuse) test drove it and no change. I also tested the diodes and they checked good. I don’t think it’s an AC noise issue but I’ve been wrong before. I might try a filter just to make dang sure

 

[KATOOM]

So it only does it when the truck is first driven? Meaning the engine and transmission is not up to operating temp? Or just every time you re-start the truck? I dont mean to repeat the question but these details matter.....

 

[Road Dog]

Road Dog: I’ll look into that, I love for it to be something simple and cheap like a loose fuel line. Did your fuel pressure drop any with the air in the line?

No drop in fuel pressure. No indication at all, even with the Chrysler scan tool.

 

[Mckelvey]

So it only does it when the truck is first driven? Meaning the engine and transmission is not up to operating temp? Or just every time you re-start the truck? I dont mean to repeat the question but these details matter.....

Not only when it’s first driven, but it is the worst when the engine is cold, first time cranking for the day. After that, say I drive to the store and shut it down. When I start back up and leave it might not do it at all until I get on the throttle, like getting on the interstate.

 

[Mckelvey]

No drop in fuel pressure. No indication at all, even with the Chrysler scan tool.

That’s good to know cause I’m holding strong at 14psi. I’ll be going to the store for some clear hose, whether it fixes my problems or not I’d like to know. Thanks for the info!

 

[Mckelvey]

I think I failed to mention, this all started as the TC locking and unlocking. I got tired of “re-learning” the APPS so I tried recalibrating it. There’s not tag on the apps that indicates the voltage it requires but I found on a different forum where people saying it should be around .529 and I can’t get anywhere near that. After trying to calibrate the APPS the issue wasn’t the TC unlocking anymore, it was this dead pedal.

 

[KATOOM]

I think I failed to mention, this all started as the TC locking and unlocking. I got tired of “re-learning” the APPS so I tried recalibrating it. There’s not tag on the apps that indicates the voltage it requires but I found on a different forum where people saying it should be around .529 and I can’t get anywhere near that. After trying to calibrate the APPS the issue wasn’t the TC unlocking anymore, it was this dead pedal.

I was going to suggest that this sounds more like its related to the transmission than anything else. If you search the forums you'll find there's other people describing similar problems with throttle conditions, and those conditions being related to a cold(er) engine/transmission. Note that this is only an issue for people with automatics too.

There was one thread I was part of not too long ago on another forum where the individual changed just about everything but the transmission and never solved the problem. That gets expensive and I think that throwing parts at problems like these isnt the best solution. I think the best solution is to see if you can find someone who has a scope which would/should help identify the issue. Since most people dont have a $3000+ scope laying around, you'll most likely have to find a decent mechanic who does and see if they can help. Preferably one who is somewhat familiar with the Cummins too. So I'd start looking at performance diesel shops near you first and see if they can point you in the right direction.