Have a check engine light, volt meter indicates alternator not charging. Multimeter verifies alternator not charging. Pulled alternator, what a pain that is, took it to NAPA, they say it's good. I know the ECM is involved somehow. Where do I go next? Thx.

 

If your battery is compleatly shot it will cause a resistance that the alternator will be unable to over come so it will not charge, also the alternator is not designed to charge a compleatly dead or low charge battery.
The alternator will only replenish what was taken during the engine cranking before start up and too keep the battery at fully charge when using headlights and/or heated screen.
so check the battery first.

 

Battery is good, tests good on a load bank, been getting me back and forth to work. I'm thinking ECM but don't know for sure.

 

The other thing is most of those auto store tests measure voltage output without load. So once you place a load on it, you may realise somethings not quite right. Most likely it's the brushes, which are very easy to check. BTW, wheres some good wheeling over there in MT? I'm just over in Williston ND.

 

I agree with Dan. You can have a bad alternator that tests good on the bench of a parts store tester. Those testers are not comprehensive by far. It is not uncommon to have "escapes" which means alternators that are bad but test good.

If there is a place around you that rebuilds alternators, starters, etc. take your alternator there. They can perform some solid testing on it that will really tell the story.

 

I understand that the testers could be wrong, but I saw him load it up and saw it measured amps and volts. I'd hate to spend the money on a new alternator only to have it end up being something else. I'll have to look for a rebuild shop. Dan91, I'm not in Montana anymore, but there are plenty of good wheeling places all over the state.

 

Maybe check for voltage right on the alternator, and/or check for resistance between there and battery Positive? Do those have issues with connections in the PDC?

It's insane what can turn out to be not grounded, I had a bolted in Alt. do it on my little dozer. I've heard of starters doing it. I suppose you could rule out that unlikely condition by grounding the alt for a second with jumper cables. (or again, checking resistance to battery ground)

Yes, I think it was 91 that the regulator moved to the PCM....

 

Well I put new ends on my battery cables and now it's working, doesn't make sense to me but at least its working. Thanks for the responses.

 

Hey Cool! And nailed exactly on your 500th post!


>>> Battery gasses have a nasty habit of helping a thin, hard crust form on the bat post's and clamps. They can look pretty good, but that micro-thin layer is a surprisingly good insulator. SHINNY! Lead is what you want. I use a pocket knife, (gently), for the insides of the clamps. For the posts I might use one of those post cleaner wire brushes, but still scrape it with a blade. If you have a condition where you have power, (dash lights ect.), then when you hit it power goes out altogether, that's a common result of a layer of oxidization there. Btw, a half *** connection could be expected to get hot during cranking, or while it's trying. Cleaning those is something to do now and then anyway, so if you are having starting problems, you might want to make sure you have bare lead on lead. Might save you some grief!

 

[QUOTE=DFlintstone;2843372] check for resistance between there and battery Positive? ****(or again, checking resistance to battery ground)

Guess it s not a simple loop like before with the PCM regulating. I can't quite wrap my head around how that works, in any case the resistance check should have found it. Glad you got it!

 

well that fix lasted about a day, doing it again. I'll try grounding the alt. directly and also will try to get a volt reading off the alt., it's a bit tight under there though.

 

10-4 on that. Just seems wires and connections should be ruled out before buying new parts. Oh and a tip from Radi, if a belt is slipping on a pulley, the pulley should get hot. There is ho hard crust on the battery posts? (shiny lead is what I want)

Others know yours better than me, it's just I've seen that usually connections are the problem. (Btw I sometimes use auto alternators for my micro-hydro power system here. Since it runs 24/7 over 1/2 the year, I change allot of brushes)(and bearings). The stators, rotors, and diodes seem to be pretty durable, and my regulator is just a resistor, a light bulb actually.

 

Thanks DF, the posts are shiny, the grounds have been cleaned up, belt tension seems to be adequate. I definitely don't have a charge voltage at the battery, the wire from the alternator runs into a wiring harness that seems to run into the cab, I'll try and get a voltage reading off that on my next day off. If that indicates the alt. is working correctly (i.e. volts 14+, probably around 16 or so since it's not regulated at that point), I'll look into a new ecm or convert it to an external regulator.

 

When you find out where that wire goes let me know! I'm having the same problem, new alternator, battery, terminal wires. (All needed to be done) but the harness to the alternator isn't getting more then 6 volts.

 

How do you convert to an external regulator? Got anything to show how to do it? With the ECM being the regulator, how do you bypass it and let the alternator have it's own regulator? I had my Jeep ECM commit suicide because it couldn't regulate the voltage from the alternator. Chrysler's design of letting the ECM be the voltage regulator is pure lack of genius, IMHO.

Best me and the mechanic could come up is that I had a weak ground at the battery and the ECM was going crazy trying to regulate voltage to it. At the end, the ECM fried itself. Actually burned up inside. So much White smoke and obvious smell of wire and insulation burning, I called the fire department and wouldn't lift the hood. The one time I did NOT have my fire extinguisher with me. Almost burned up my Jeep!