Troubleshooting throttle surging

[96ram1500]

I am relatively new to the forum but have heard of Moparman and used his wiring maps for a while. They are very useful. Very good job.

My throttle surging issues are caused by varying voltages to, and subsequently from, the APPS. I have the same issues with the alternator and/or PCM disconnected. The issues are as follows:

-Truck starts right up but idles erratically

-engine idles fine with ECM data lines disconnected from VP44 (wires removed from connector)

-engine idles fine with APPS disconnected  (no fluctuations in incoming voltages)

-40 HZ (or thereabouts) "signal" in power and ground with and without alternator (oscilloscope screenshots available, Spike at about every 25ms and .5V)

This is s perplexing system as I can't tell if the VP44 is injecting this 40Hz signal and causing my ECM to throw a fit or not. The ECM is obviously  giving an unstable voltage to the APPS and  not liking what it gets in return. I just don't know why it is supplying an unstable voltage when it is supplied a stable 12v. This is very confusing. Can anyone shed some light on this 40 Hz so I can  narrow down my search? Maybe its coming from the tach signal from the VP44? I haven't checked to see if it changes with RPM's but I will. As stated, I am relatively new to the site so if  this has been covered, feel free to make me look stupid.  

 

[Mopar1973Man]

Simple solution. 

 

Test the alternator for excessive AC noise measure the AC voltage at the BATT post of the alternator and ground. You might end up replacing the alternator diodes or alternator completely.

 

Now do the W-T ground mod.

 

Or the simple version...

 

 

Edited July 29, 2018 by Mopar1973Man

[Dieselfuture]

Do you have a stock apps, if so throw it away and get timbo. Then like mentioned check alternator and do ground mods and check all other grounds. I know you said you disconnected alternator but damage to ecm or vp could be already done, may need to send out ecm for repair. If you do be very specific on what it does and codes associated with it, any codes? 

[RottenMutt]

fastest thing is to check is the ground wire that goes to the passenger battery from the harness from behind the alternator, check the splice connector, wire to battery terminal, check the positive crossover cable by checking for a voltage drop from positive battery post to positive post (should be zero voltage), and clean the battery terminal(s). 

 

are your diodes good in alternator?

 

if none of that fixes it then do W-T mod, even if it fixes it consider doing the mod.

Edited July 29, 2018 by RottenMutt

[96ram1500]

That was a very quick reply. Kudos Moparman. I will try to post my alternator waveforms and see how you read them.