Well another issue and sorry for the long post.

I posted about the battery issue in my "Plugs Away" post. After replacing the battery, and changing the plugs/wires a few days ago, he goes out to run some errands and his battery light comes on again. It lights for a minute or so and goes back out. Double check the battery connections and triple check the Battery voltage under load and get the same results as before. High 13's at idle, no load. Mid 12s at idle with everything one. Rev to 2K and it's back up to high 13's even just over 14v.

So check the belts and notice the alt belt is a bit frayed and does feel a bit loose. So I replaced the the belts (pwr steering/ac as well, it was pretty bad). I also pulled the connector off the alt to spray some cleaner in it. Get the belts tensioned. Start it up and check for charging voltages, all looks good.

He goes off to run some errands and about 40 min later, tells me the battery light is on and this time won't go out. He makes it home and I put the voltmeter on and with the engine running it reads just over 12v Rev the engine and no change. The new belt also feels pretty loose and even squealed a bit when I rev'ed it (I had intended to retighten the belts after he drove it a bit anyway). Scanned for codes and got a P1631. While tightening the belt, I pulled the alt connector back off, sprayed some more cleaner in them, use my airgun to blow them out. Reconnect everything and it's charging again. I was pretty sure I fully seated the connector but perhaps i didn't and it came loose. I didn't see any signs of oxidation or other corrosion on either side of the connectors.

So it's definitely charging. I used some long alligator jumpers to extend my voltmeter leads into the cabin so I could monitor the battery voltage while driving. I also turned on combinations of head lights (with and without fogs) and AC (with different fan speeds) to see what happens.

In summary, driving with no lights or AC, voltage remains mid-high 13's even crossing 14v and coming back down but mostly high 13s. Come to a full stop, trans in drive, voltage drops a bit a first but back up to mid-high 13s. While driving (we're talking under 40 mph), voltage remains high 13s. Turning something on drops the voltage a bit but climbs back up. However with lights and AC on max, when coming to a stop, the voltage slowly drops to mid 12s. Accelerate (or just put in neutral and give it some gas), voltage climbs back up again into the 13s. My scanner is still unable to reliably test the battery (it's new), but the alt test still passes.

So while dropping to 12s concerns me, it seems to be fine once I get going. The FSM details how to check the charging system but not by measuring battery voltages (at least I couldn't find it). So before I start pulling up carpet and going through the detailed steps, checking voltage drops, etc., does this sound normal? I don't want to fire the parts cannon (again) and just swap in a new alt unless I have to do so. I certainly don't want to start tracing wires and probing connectors but will if I have to.

Thanks for any help.

 

Well it hard to diagnosis this old a vehicle with a charging problem that is still OBDII on a forum... but I suspect a failing generator? That is a PURE GUESS because tha e other would be a failing ECU/PCM and again this is prure guess and I did consult with my .................eight ball.
You need to use your scanner and test the ECU/PCM charging cycles on the live scope screen of your scanner. If you don't have one or an oscilloscope your trouble shooting this charging system my present a DIY challenge and a half for you. Sorry.

 

I used to see that light activity on Bosch alternators when the voltage regulator was beginning to fail.