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PCM fried from jumpstart....

whitexj98

NAXJA Forum User
Location
Cali
(Edit: Shoud read PCM fried from jumpstart)

So my jeep was completely dead yesterday. I have something draining the battery and it doesn’t get driven much. So I attempted to use one of those high amperage jump start/ chargers but it wasn’t enough to get the motor to turn over much, I tried it probably 3 times and gave up. So I put it on trickle charge for 4 hours or so and unplugged it for the night.

Today I go to try to start it and it just cranks. I also notice the fuel pump is not coming on. So I hook up a scanner to see if the CPS is reading, and I only get like 2 PIDs showing up??

So I check all fuses and what not and even kicked the fuel pump on by jumping the relay, I hear the pump but it still won’t fire. So I’m thinking PCM is faulty so I throw in a spare PCM that’s only problem is the fuel pump ground driver is fried on it, so I ground the fuel pump driver and jeep fires right up....

So my PCM is shot and I think it might be from the jump starter thing. And no I didn’t not hook up the terminals backwards...

Any thoughts??
 
Re: PCM fired from jumpstart....

I had that blow the PCM-B fuse (there was an A and B fuse on the PCM), on the 2001 Saturn not long ago. Would not start, OBD-II could not find the PCM, and I got lucky, it blew a fuse first with out eating the PCM!!!!
 
Re: PCM fired from jumpstart....

Jump starting a Chrysler product is a risky deal, there is no regulator in the alternator, it’s in the PCM. I suspect your diodes are leaking and when the PCM full fielded the alternator in an attempt to charge the dead battery it, it wiped out the ECU. Putting the regulator in the PCM is brilliant, today you see this in high end vehicles and Chrysler did it in the early 90’s however the one problem is alternator regulation generates heat, too much heat and it can melt the board connections. At this point I would bench test the alternator, if you have shorted the rotor coil you may cook the new one.
 
Re: PCM fired from jumpstart....

Interesting, I had not thought of that, but I knew they moved the Volt reg to the PCM.

In the 1980's I wiped out a dodge (chrylser) alternator every single time I jumped started another beast. It was not immediate, sometimes it would be a few days I would notice the head lights dim, and then eventually a dead battery in 3-6 days. It would take out half the diodes, and then drain the battery with head lights on at night. I went through 8-10 alternators before I made the connection.

One thing I like about Renix AMC jeeps is they don't SEEM to have the same problem.
 
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