patdaly

My stupid Ramcharger is still driving me nuts ( OK, the Chrysler wiring is ). I have verified the Alt. is good, swapped another one anyway, traced wiring back to the PCM, and other than doing tests such as the carbon pile load test ( don't have one ), done everything that I can think of to make this stupid thing charge.

Thinking back to the last time I was playing with it, I had 12.05 volts at the batt lead ( obviously battery was discharged somewhat ) and 11.45 V at BOTH the 12V feed and sense lines at the alt. Now, I remember reading that sense should be lower than the 12V feed.

What could cause the voltages to be equal?

I swear I am about ready to throw a external regulator on this thing and yank the check engine bulb.

cougar

1st question. Do you have low voltage or no voltage out of the alternator with the engine running?

thrashingcows

What year is the wiring on your RC...92/93 I would assume? Have you replaced the relay on the inner driver fender? Maybe it's all fubar'd up inside and causing this situation?

patdaly

Definitely no charging Cougar, voltage at the Bat terminal of the Alt is 12.05 and drops with time, it is roughly 1/2 volt higher than the field and sense though.

Thrashing, this is on my Gasser 90 RC, it has the PCM regulated charging the same as the 92/93 diesel setup though.

I guess my main question is, if the voltage feed from the ignition switch is the same voltage as the PCM, not charging would make sense, the way I understand it's operation, it tries to charge to get the error ( difference ) between the 2 as close to zero. If that is the case, it is working perfectly, and the real issue is what is allowing the 2 voltages to be the same?

Does that make sense?

j_martin

If you have 12 V on both field terminals, then the regulator (PCM if stock) isn't working or the connection between the PCM and the alternator is broken somewhere.

12 v is supplied to the alternator field. The PCM grounds the second terminal to make field current flow. If the second terminal is at 12 v, then it's not being driven to ground.

It's pretty simple to trace. If you check the terminal on the pcm and it's at 12V, then the PCM is not running or is bad.

On the not running, what else doesn't work?

cougar

I would say that is were part of your problem is. It should be the same voltage. The thing is, with a low(er) voltage at the sense terminal, it should be over charging. The way it works is you have battery voltage on one field terminal and a varying resistance (regulator) to ground on the other. In this case it could either be a high resistance or inability to carry the load on the regulator wire or the regulator itself.

torquefan

This. The ASD relay supplies 12v to one side of the field winding. The regulator in the PCM provides the ground to the other side. If you're seeing the 12 on both sides of the field winding, it means nothing is grounding the other side. Theoretically, if you apply ground momentarily to the side of the field that goes to the PCM, you will full field the alternator and it should start charging at full bore. Only do this momentarily as voltage levels can rise above safe levels pretty fast.

patdaly

Thank you all!

I don't know why I still keep approaching this thing with my GM thought process, but I do.

PCM grounding makes perfect sense now, I shall attack the ground side instead of the 12V side...... I do have a spare PCM so I might also throw that at it to check.

patdaly

Ok, to bring this one to a close.

Grounded the green, had immediate full field charging. So, I wrung out the wiring, and for the life of me, could not find a THING wrong with it.

Changed the PCM, voila!

I just find it ironic that the guy here who always posts that 99 percent of the time, your problem isn't the PCM gets bit by a bad PCM.......

Oh well, if ya can't laugh at yourself.....

thrashingcows

Glad you got it figured out. And that's what's great about working on these old trucks...we are always learning.