WOT upon starting

[DRGABE]

Any help appreciated.  1999 24v air dog lift, timbo apps, edge comp box.

Start the engine and it runs up to full throttle without pushing the pedal. Is this an ECM issue? No codes thrown, thottle cable intact. I'm at a loss here.

[Mopar1973Man]

Gotta ask a few questions?

 

Does the WAIT TO START light come on instantly? 

Does it still do it with the Edge Comp removed?

What does the live data tool show the TPS value to be with just the key on?

Does the TPS show normal reaction without the engine running?

[DRGABE]

Been having issues with the WTS lamp. Longer delays, sometimes never lighting. Haven't disabled the comp box. As far as the rest, I don't have a live data tool available until Monday or so.

I did install the high idle switch years ago as well.

[Mopar1973Man]

Already strike one with the wait start light.

Strike two with the WOT after starting.

 

I'm betting you have not done the W-T ground wire mod? Then I'm also betting your alternator has excessive AC noise issues?

 

[DRGABE]

Correct,  and alternator was new in 2019. Wouldn't know about noise issues. 

Not familiar with the  former.

[dripley]

When my ecm went WOT at startup was one of the many symptoms I had.  Did not do it every time. Sometimes it would go WOT on its own or when I touched the throttle. Pretty much had a mind of its own. Also had a pile of codes. 

The AC noise Mike speaks of can be present even in a new rebuild. The only know is to test it. These truck really need clean DC power. AC noise is very harsh on the electronics. Here is one good article on the subject. @Mopar1972Man has one also in the articles section. The ground mod is explained there also.

 

[Mopar1973Man]

Then my 3 articles about this topic.

 

 

 

[DRGABE]

Are you suggesting that any one of these three could be the cause of the WOT condition? Or they are modifications I should perform as prevention.

[Mopar1973Man]

Basically the ECM is shot and will require to be pull and tested and repaired. 

 

The articles above are to prevent future failures or testing for conditions that might cause a failure. Sine your ECM has failed your going to need to repair it first but you not going to want to install a ECM to possible bad condition that might cause it to fail again in short time. 

 

Basically in a nutshell AC noise is really hard on electronics the AC pulses force apon thing like digital chips and other part that ain the family of diodes and transistors will take damage fairly quick. When the polarity swap back and forth this creates heat on these parts and hence the failure. 

[Doubletrouble]

 The WT ground mod like they mentioned is a preventative measure. It's not difficult to do, takes a little bit of time but more than pays for itself in savings later. Clean DC power is must to prevent issues like what your having. I was unaware of it myself until reading here about it. I tested for a/c noise twice, did the mod and tested again and was amazed at how much it cleaned it up. 

 Good luck, follow the advise here and you'll be back on the road soon. Lots of info and experience on this forum.

[dave110]

WOT for how long after start-up? 1 second? 1 minute? Does it happen every time or just after sitting a while, or just hot, or

just cold?

 

 

Edited January 3, 2021 by dave110

[DRGABE]

WOT immediately upon start, no pattern yet, and I don't let it run a course. I can't bring myself to peg the tachometer indefinitely. This condition just began. 5 attempts to start were made, coolant temp was maybe up to 160 or 170, outside temp in the 30's and humid. I did let it sit over night where it stood, and the batteries were drained enough that it wouldn't turn over. Batteries were just cleaned and load tested within the last week, all was fine.

[JAG1]

What do you mean the batteries were drained? Are you saying the batteries drained down just overnight without anything left on?

[dripley]

How old are these batteries? If they were fine just a week ago but died overnight something else maybe going on.

[DRGABE]

Batteries are from 2016. Truck was towed to the shop, charged up and it started/idled normally.  He's running diagnostics with scanner and checking for shorts etc.

[dripley]

i would show him the reticles that linked in this thread. if he's not used to working on them he wont be familiar with the things we have all learned here.

[Doubletrouble]

 I agree with droplet, if the shop is not familiar with some of the nuances of these trucks and the little tricks that keep them on the road he may diagnose something else. Once you get the truck back do the WT ground mod if the shop didn't. Check for a/c noise as well. There are many knowledgeable people on here to help with whatever you get into. I have learned alot in the months that I've been a member. 

[DRGABE]

I'll let him know, and definitely do the ground mod upon return. Thanks for all the tips and advice.  

[DRGABE]

Okay, new batteries, cleaner connections, starts and runs fine. A few days went by and the WOT occurred again during mild weather and half warm engine (something keeps nagging at me about the fuel choice too, I don't know why). Did the ground mod the day after and figured I'd do the PCM blue wire next week, all better, around 2 hours work like Mike stated, not rushing anything.  Thought I'd go a step further and add the 150a breaker on the alternator charge wire ......and trip....trip several times. Did I read right, that is and indication the diodes are shot? Before that addition all seemed right. Haven't quite figured out how to test the ac noise properly yet, but learning slowly.

 

[Dieselfuture]

7 hours ago, DRGABE said:

Haven't quite figured out how to test the ac noise properly yet, but learning slowly.

It does sound like you might have some alternator issues that led to ECM damage. If you're not touching throttle/apps sensor, ECM is in control of idle. So if it goes to full throttle I'd say something going on there, but you do need to make sure you're apps isn't doing anything goofy with some sort of life data tool.

Ac noise is easy to check but conditions have to be right and you have to use a good voltmeter cheap ones don't work. Check it with engine fully warmed up preferably after you drive it, park it and don't shut it off, take a good voltmeter set it on ac voltage, check it on the stud of the alternator with positive lead and you can go on the body of the alternator on the negative, make sure you're getting good solid connection. If you test it on batteries it will be a false reading because batteries act as a filter in the way and take some of that AC noise out, but it's still traveling through your system causing damage and funky behavior.