DunnerCummins24

Thanks for both your responses! Couldn’t trust it on our most recent camping trip so we ended up renting a tow behind and pulled it with my 21 Ram. I did use a multimeter when installing the APPS. I’ve had time lately to drive the truck more with the voltmeter rigged up and the trucks been driving great… zero issues. Was thinking and not sure if I’m on to something here. Was wondering what’s different with the meter hooked up and was thinking two things. Maybe a connector issue at the plug from the APPS and with the back probe in its making a difference? I think number 2 is more likely, now with the meter hooked up I’m giving the apps a ground, from my understanding the sensor grounds through the ECM? Wondering if I run a ground wire from the ECM to the battery or known good ground and see what happens? Today I took it for a quick boot with the meter unplugged but still drove fine but will need to do this more to see if there is a difference.

Just getting back from a wedding today and gonna take the truck for a boot today and tomorrow and see if I can get it to act up and see what the meter does. The set screw I have a dab of loc tite and a markered line indicator on it because I was having issues with it moving but it’s still all good and yeah the cables move freely. Is the .058 vac a concern? That’s everything off and fully warmed up. But usually the truck acts up in the morning or first start when my vac is .1 and up. Just wondering if I had an alternator with lower VAC when warm if that would then correlate to lower numbers when cold. I do have another reman alternator in the box I could try if it’s worth it.

So I rigged up an analog volt meter and ran two wires through the firewall. Ones back probed into the signal wire and the other is from battery ground. I tried to drive the truck Tuesday and couldn’t even get it out of the driveway. So I figured this is a perfect time to test this with the truck acting up. I did also clear the codes. But I drove 35km to work and 35km back with zero issues, truck ran great. I did test it with key on engine off and took the APPS through its range on the voltmeter and it was perfectly steady without hesitation. Now I just have to keep driving it to catch it when it acts up and see what the volt meter does? Also all my AC voltage tests were at first startup so I checked it after driving home with everything off and it was .058vac.

John, Thanks a ton for laying that out, i will 100% be doing that. Do you think that would cause my issue? We are supposed to go camping again next weekend and I don’t have a whole lot of time. Two questions I have are I was going through old threads here and saw moparman said for alternator AC noise that .05 is marginal and .10 is failed. I was having .7 with accessories off and .125 with everything on. Is that an issue? I had some other guy tell me that’s totally fine? Also saw a test on blue chip diesel on back probing the APPS and seeing if the voltage increases when the throttle kicks up, they said to route it into the cab and check it while driving with an analog meter. But it’s doing it consistently at idle, that’s something I could check fairly quickly and easily.

I didn’t use the starter as load when doing the tests, are you able to explain that? Have you seen many Timbos go bad? All my wiring between APPS and ECM is good. Timbo is maybe just over 2 years old. Thanks for checking that out on yours.

I was just checking across the wire from end to end. Honestly I can’t remember which wire it was, I just took pictures of the multimeter readings. I should have recorded it better. And okay sounds great thanks. My readings are zero unless I’m on the throttle, but I did notice the odd time while I’m cruising it dropping out to zero but that could be this scanner, it’s kinda slow and laggy. And then now I’ve noticed it going up when the trucks revving and my foots off the throttle.

So weeks ago I did perform some voltage drop tests on a bunch of the cables, a lot were like .1-.2, one was .5 I think. Again truck ran great after having the ECM unplugged and doing all those tests. Then we left to go camping last weekend and of course acted up, really just idled high at 1100 and surged a bit but got us there and was fine on the way home. Went to take it for a ride this morning started increasingly slowly idling higher and higher, kicked back down for a couple minutes then snapped to like 2000 and then I just shut it off. I have been cruising around with scanner on and watching the APPS pid and have noticed with no throttle input I am getting an APPS %, I’ll attatch a picture from this morning when it was acting up and foot wasn’t on the peddle. Tried a APPS reset after it was idling high this morning but that’s when it snapped to 2000 after that. Thinking it has to be electrical the way it can just go away for weeks when I’m messing around in there? Really leaning towards the ECM now.

Thanks for the reply John. Splice 165 is where the 4 wires were taken to the back of the timing cover all together? If so that splice is good. My battery cables are as old as the truck and same with the main grounds coming off them. Not sure if it would be worth changing them? Was looking at a 240a mechman alternator with the full kit to change all the cables. But by the time I get it to Canada I’m looking at 1700$ and probably isn’t going to fix it, would just be nice to have that done. I have a suspicion of the ECM, but not 100% sure there either.

Checked all 6 this morning from connector to ECM and .2 for all pins, even 32 which was reading higher yesterday. Wiggled the harness and pretty much stayed the same. Key on terminal #5 am getting 5.1 volts. Checked between the pins too for shorted together wires and nothing. Put everything back together, plugged alternator back in. Cleared codes and did a APPS reset. Drove the truck for 10 minutes zero issues. Couldn’t even get 2 minutes past my house yesterday lol

Hey John, Yeah did test on meter first. I’m gonna try 32 again and wiggle the harness and see if anything happens. Is it worth checking the other 3 pins? Gonna spend some more time in there this morning.

Did what John said and pinned out between APPS and ECM and got these readings. 25 .2 32 .7 31 .2 All in ohms.

Haven’t had time to pull alternator but took it for a drive this morning, started acting up right away. Shut it off and got out unplugged alternator. Truck ran great for a couple blocks and then started doing it again, if not worse than when the alternator was plugged in. Still throws the same code P0121 and I’ve got a P0382 which is unrelated I’d think. Any insight which direction I should be looking now? APPS? ECM? VP? Wiring?

Yeah that would have been a good idea. What would you recommend as next steps? From what I’ve read online my readings are way high, but from the guy I talked to yesterday he said they’re fine. Should I pull the alternator and send it out? I was going to try driving it this weekend with alternator unplugged and see what happens.

Talked to someone today at a alternator/starter rebuilder spot, and the guy makes wiring harnesses and rebuilds alternators and he said those values are fine but sounds like I have a wiring or ground issue, especially since after I did the WT ground mod it was better for a few weeks then came back. Was saying that sounds like when I did the ground mod I had “touched” whatever the problem was or affected circuit since it did get better for a short amount of time.

Hey guys, been a bit since I last posted. I didn’t drive the truck much over the winter but when I did zero issues. Now it’s warming up outside here and starting to have problems. Drove it last weekend and took me 20 minutes to do a 10 minute drive. Dead pedal and revving up on its own. Sometimes it would dead pedal and id pull over, wait a minute and then the throttle would be back without clearing the codes. It would happen again and sometimes I would restart it and it would start revving high right away at the same high RPM like when I shut it off. Eventually I left the code and kept trying to get where I was going and it surged a bit while I was driving but eventually ended up being okay. I brought my multi meter home from work and checked for AC noise because I’ve been suspect of the alternator. With the truck running right away with lights, radio, defrost heat, grid heaters, etc. I was reading .112-.185 depending if heaters or compressor clutch was cycling. With heat shut off I was reading about .071 and seemed to be coming down as truck ran longer but I usually have problems when I first start driving. From what I’ve read these readings are way to high? Am I looking at a new alternator here? If so what’s the go to? Looking at getting a 170 amp and have looked at nation and mechman. Thanks!