Been fighting with a really strange issue. I used to have strange power issues and dead pedal and the tach would bounce around and die every now and again. I have since diagnosed the dead pedal back to a faulty factory apps and replaced that with a timbo unit. That actually seemed to fix almost all the issues. Maybe 2 weeks after all that, I went to the dealer and finally had high idle programmed into the truck. The high idle has not kicked on at all, and yes it is cold enough, and I'm sure the sensors are reading correctly, I'm going to double check tomorrow morning. But recently, within the past 3 days, I've had an issue where the alternator will stop charging for a couple seconds to a minute, then randomly start working again. It's weird to me that it throws the cel for a split second and turns it off, you would think it would leave it on after it sets. One of the times it stopped charging, it almost seemed as the truck was in limp mode, I had no power. And as seen, sometimes the water temp acts erratically with it.

You need retrieve the trouble codes. You are bound to have some. The CEL can and will turn itself off on occasion but the code should remain. 

A week ago after the first sign of this symptom I checked codes and got P0320-Crankshaft position sensor from the pcm, and P0521-Oil pressure rationality from the ecm. I cleared codes. Drove the truck for a the next couple days, this happens multiple times throughout the day. I scanned again now and just got the P0521 code from the ecm. That's another issue I'm having that I'm going to try and figure out later. Sometimes when I start the truck in the morning when it's cold, it'll say 0 oil pressure on the cluster, and wont go to normal pressure until I shut down and restart. I know pressure is fine though.   Back to the original problem, I'm wondering if it's starting to look like an alternator issue more then a pcm issue. I took a live graph of the apps while the truck was running. The voltage was steady at .65 but every now and again it would kick to .67 for a split second. The rpms go up about +/-50 when it does that. Maybe also why the high idle doesn't work, idk.

What year is your truck and how are you checking for codes?

It's a 2002. With a Mitchell scan tool.

The 320 on an 02 would be the cam sensor. If it is failing intermittently it will drop tach signal and can stop the engine from running. 

 

The 521 is a funny one in that unless you have a rare 02 you oil pressure sensor is nothing but a switch and not a sensor. When you start the engine and the switch sees 6 lbs of pressure it signals the ECM to take over and bases oil pressure on RPM, and ECT sensor readings. It is quite convincing in how it works. I bought my 02 in Oct of 2001 and this is what it came with. The way to tell is to look at your sensor/switch harness connector. If it has 3 wires it is a sensor, if it has 1 wire it is a switch. 

 

I assume you have checked your oil pressure with a separate gauge to be sure? The oil pumps in these Cummins are pretty bullet proof. 

I haven't checked it with a mechanical gauge quite yet. I'm sure it has oil pressure though, otherwise it probably would've blown up by now haha. I have been trying to dig into troubleshooting the cam sensor but don't have much time to keep tearing it apart. I've done many continuity test on the engine bay wiring and haven't found anything bad yet. Considering I'm about to roll over 340k on original parts, it's probably time to replace some sensors haha.

It could be wiring and not a sensor. I just spent quite a long time fighting electrical gremlins. I hate them probably more than you do. I only had one sensor that failed and my gremlins were mainly tied to the 5v supply to the sensors. The sensor grounds can do the same thing. How is you electrical system, as in the alternator, batteries, cables and connections? Weakness in these parts can cause trouble tool. 

 

I most recently fought a loss of power issue that was like the limp mode you described earlier. I did get a 237 map sensor code sometimes when it acted up but not every time. That did turn out to be the sensor. I was also able to see the signal come and go with mine Scan Gauge. I might hurt to check your oil pressure harness and see which you have. I have read about bad OP sensors, 3 wire, causing other sensor issues. Long shot but not hard to do. 

Batteries are brand new, ran new wiring and ends to both batteries and cleaned all of the grounds. That did make a huge difference in starting and normal performance. I'll have to check that sensor out next time I get out there. Little wiring things are the worst to deal with 

I'm also starting to think that I should go back to the dealer for the high idle issue and have them double check they actually programmed it. It should only be IAT, ECT, APPS, and making sure the brake isn't on, correct? It meets all the criteria but still doesn't engage.

I believe you are right. But if the apps is going up as you stated that in it self could be enough to not let it come on. I did not notice do anything strange like that in your video. Was your truck warmed up in the video but the gauge not reading right?

It usually only has that slight surge in park and idle. The video was in drive at a stop light. It's only a .02v increase, this shows it a little better. It's not very often. I might try and back the idle screw out of the apps just slightly and see what happens.

I got timbo apps years ago and never looked back 

Yeah, I already have the timbo apps in there.

Thats not much at all for sure. Not enough to take it out of idle. Back when I had surging issues it was more than enough to kick my exhaust brake off. 

Yea, that's what I was thinking. I'm going to plug the scan tool in next time I start it in the morning and make sure all the parameters are reading correctly, if they are, its going back to the dealer.

Timbo's apps is about angle than voltage.