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TXRIVERRAT
July 19th, 2010, 10:10
I know this is a beat to death subject and I've searched, but I wanted some input on the conclusion that I've come to.

96 4.0

Basically it's running off battery power only, no alt output to battery. I pulled the pos cable from battery while it was running last night (I know) and it died immediately.

Quick run-down: replaced cables (battery to starter, alt to pdc, pdc to battery), replaced/cleaned battery terminals, cleaned all grounds I could find, replaced battery (before I realized it wasn't charging). I have also pulled the alt and had it tested at O'Reilly's and they say it's good. The only thing I haven't done yet is to test the "field" terminals on the back of the alt.

After a couple of hours of reading this morning all indications are that either the alternator or the voltage regulator which apparently is in the alt are bad. So, since I know it's possible, how probable is it that the test at O'Reilly's was wrong? Could the alt pass that test while the voltage regulator is bad? The guy asked me if the vehicle had an external voltage regulator which I wasn't sure of at the time and suggested that might be the problem, but since it's in the alt that he tested what now?

This is my wife's dd and she's not happy having to shut off the AC in order to make it home when it's 100* outside!!! lol

Thanks in advance!!!!

Pelican
July 19th, 2010, 10:40
Voltage regulator is in the ECU/PCM, not the alt. Best to take it to an automotive electrical shop for a proper test. They can repair it right there.

In the meantime, if you haven't already done so, you can test at the battery terminals with a meter -- should get around 14+ volts with the engine running.

Let us know.

Edit: Guess you're going to have a tough time checking the voltage with the alt out of the truck! Good that it's already out though...

old_man
July 19th, 2010, 11:18
What ever you do, don't disco the battery with the engine running. That is a quick way to fry the ECU.

kastein
July 19th, 2010, 11:19
Yep... take that trick out of your bag and bury it, that's only a good idea if the vehicle you're working on has points, a condenser, and carbs.

TXRIVERRAT
July 19th, 2010, 12:34
Alt is back in the truck. I had it tested last week some time, I've been checking/replacing little things each evening trying to get it fixed. I knew my old trick wasn't a good idea, but I tried it anyway. I can check the voltage at the battery with it running tonight, but I'm quite sure it'll only be whatever the battery has. Basically we've been putting it on charge anytime she's at home and she get's back and forth on whatever the battery has in it. It'll go til the battery goes dead and then it dies which also tells me the alt isn't putting anything out.

The hard part is that I work 7-5 and the wife works 4-10 or so which only gives me a short time to work on it each evening after she gets home.

Although I didn't see a timeline, I took it that it was later models that had the regulator in the pcm, that sucks!!!

joe_peters
July 19th, 2010, 17:32
As said, the 91+ are equipped with Nippon Denso alternators and they are regulated by the PCM.

Now, also as said take it to a competent shop to have the problem diagnosed. The "chain" parts store testers often report FALSELY that the Nippon Denso alternators are good when they are in fact BAD.

As the alternator and PCM are both a little spendy you may seriously want to consider spending a little money for a competent diagnosis.

Good luck.

winterbeater
July 19th, 2010, 18:22
It is not necessarily just the alternator or the regulator. It could be the wire or connections between the two. Clean and test for continuity.

joe_peters
July 19th, 2010, 20:15
It is not necessarily just the alternator or the regulator. It could be the wire or connections between the two. Clean and test for continuity.

Yes. :D :worship:

TXRIVERRAT
July 20th, 2010, 04:59
It's fixed! After swapping PCM's didn't fix it I swapped in a known good alternator and it worked. I was lucky that we just pulled the drivetrain from my buddy's Jeep last week so all these good parts were literally up the street from me.

So just as y'all said, the test performed by the chain parts store was wrong!!!

I thank you and my wife especially thanks you for the input!!!!! :cheers::cheers::cheers:

joe_peters
July 20th, 2010, 09:28
Glad you got it squared away.

Good luck, happy wheeling.

orange
July 20th, 2010, 10:07
...It don't get no better than "Wife Approved"!!!!

:cheers:

Well done.

Regards,
Orange