96 Rodeo PCM (electrical) issues?

Recently my wife got a 1996 Rodeo from her sister. The only issues with it at the time were a worn positive battery clamp, and the LF lower control arm had 1 bolt missing, and another rather loose. I replaced and tightened the lower control arm, and the rodeo drove "like a dream"

.....For a week that is. Now this week has been a disaster. ALternator went bad at same time the A/C quit working. I replaced the alternator, and although it worked that day, the AC did not, and the voltage never read above 10 1/2. I knew i had an issue. Next morning, "dead". Took the alternator out, and it showed defective at Auto Zone. Got a new one, put it in, didnt even work from the start. Took it out and back to auto zone...Passed 5 straight tests. I now have the new working alternator in, and yet nothing.

I can jump the rodeo, but the second i unhook the jumper cables, she dies. I verified everything was plugged in correctly, and the battery is good. I ran a volt meter on the 4 prong hookup for the alt. and noticed that the bottom right prong ( looking with tab on top) showed no reading. I figured it might be a ground, but someone told me that is probably the wire that goes to the PCM that is under the center console. Now i am thinking that since the PCM probably controls the AC to some extent also, and the fact that the gauges were all going nuts, and the gas gauge reads incorrectly, that i have a faulty PCM.

Tommorow i am going to see about replacing the PCM.

COuld someone tell me if i am on the right track, or any ideas at this point would be great.

Rodeos built after mid-1996 and through 1997 require a different alternator from those built prior to mid-1996. Chances are the alternator that you got from AutoZone is for older Rodeos and therefore doesn't have a connection to the pin you checked. I would be willing to bet that if you get the correct alternator your problems will be solved.

Mine was made December 95. All the plugs and things match up perfect.

Also, i know Reman's are not recommended, but to not even work at all is kind of odd to me. If these things didnt even work for 5 minutes, i dont see how they can sell them. Plus, i cant afford to just accept this $150.00 loss and go buy an all new alternator.

Im stumped.

SO just to sum it up. The AC and Alternator crapped out at the same time. Battery was only 2 weeks old at the time. 2nd alternator was defective upon purchase. 3rd alternator didnt solve issue, but tested good at auto zone (5 tests straight).

If i charge the battery, it gets me about 20 minutes and dies. If i jump the rodeo, it dies the split second i remove the cables.

The one thing i know that controls the AC and alternator is that PCM under the center console. But im not too sure to what extent. All the cables under the hood are in great shape and seem fine. All fuses are good. Have double and triple checked the installation of the alternator, and the battery cables are rather new also, and very snug.

Any ideas? I am open to try anything to fix this thing. it's Killing us being down to one car with kids in school, 2 seperate jobs, etc...

thanks.

Don't worry about the A/C. When the alternator is dying or producing low voltage, the fan will cut out, and when the fan isn't on, the AC light wont light up and the compressor wont engage. Those crazy dash lights are part of the dying alternator syndrome. Wierd, but true.

The gas guage is a common, but completely independent problem. Most will read somewhat incorrectly due to the sending unit. It's unlikely to be related.
But:
These trucks are VERY picky about thier alternators, and HATE remanufactured ones. I went through 3 of them (one lasted a week, another didn't work at all) before I found a functional one. Quite a few people have had grounding problems with the alt and batt connections, and it sounds like this is your culprit. Make duplicates, clean the old ones, test and test some more.

Something suspicious to me is the fact that it dies right after you unhook the jumper cables. Even with a toasted alternator, your truck will run for a good while with only the battery powering it. (Ask me how I know, see alternator dying comment above). If your battery is good, there is a vital connection between it and the truck not being made. I would bet the ground strap.

Well it doesnt die right away when the battery has a charge, it dies when it has to be jump started because there is no juice left. If i fully charge the battery, it will run until the voltage meter gets down to around 0.

I did speak with the dealer this morning, and he said the Alternator has a ground in the 4 prong. Thats not what the haynes manual shows, but oh well. Simple fact is the alt isn't charging the battery.

*update* called a 2nd dealer and he said that the alternator DOES run off the PCM, and said that is likely where the issue is. This info at least matches the manual which shows that prong not getting juice to the alternator is a wire that runs to the PCM under the center console.

Did you remember to hook up the alternator positive cable? It's separate from the 4 prong harness. If you did hook it, make sure the connection is tight at BOTH ends, and that both are impeccably clean. Also, check the wire for continuity.

I still really doubt the PCM has anything to do with it. The reason the alt is connected to the PCM is that to save gas mileage, the PCM de-excites the alternator to around 12 volts under hard acceleration, and back up to 14 once the engine is under less load.

And per my previous post, forget about the AC. It will fix itself when you fix the alternator.

Yes, everything is right. Local mechanic looked at it and told me that there is a short somewhere in the line between the PCM and the alternator. So at least i was not far off track with it. Thank god, dealer quoted me 850.00 for a PCM. Time to trace the wire and find the short.

Hopefully this will be done tommorow.

Fixed. Line from alternator to PCM and a different wire were both shorting out. DOuble your pleasure i guess...lol.

Volts show good, and A/C lives again :)