Alternator Overcharging Problem.

[BigAL]

This has to do with my '99 Z28, the car ever since I bought it has had a low alternator output at idle with the A/C on, in the summer time it'll read about 11v on the gauge on the dash, basically just above or at the red zone line, to cure this I installed an alternator from Mechman Alternators, it's a 170amp model, my problem is the alternator is pegging the volt gauge on the dash at first/cold startup and then settling down to 17.1 volts, my car is throwing system voltage high codes. I called Mechman and they said to run a negative cable from the battery to the mounting bolt on the alternator, so I did that with a 4 gauge wire, i'm also running 2 gauge wire for the positive cables. And even after checking all connections and running the new negative cable the alternator still does the same thing. So my question is do you think it's an alternator problem or am I missing something that would cause this. The alternator also has the oval 4 pin connector but it only has one red wire that goes to it.

[Scott Liggett]

Internal regulator isn't working right would be my guess.

[BigAL]

Internal regulator isn't working right would be my guess.

That's what I'm thinking to, but there is the chance that they setup the alternator for the wrong voltage, they make alternators for 12v, 14v, and 16v systems, if this alternator was setup for a 16v system it might explain why that alternator settles in at 17v. I'm just seeing if anything else could cause the alternator to do this, you know anything I might be missing.

[Deaf Bob]

Measure it at the alt with a multimeter to confirm what your dash guage is saying..

[BigAL]

Measure it at the alt with a multimeter to confirm what your dash guage is saying..

Did that Bob, it is reading 17.1 volts, that is after it warms up, it's a couple more volts higher when it's cold.

[black widow]

Hey big al I've run into a similar problem back in 98 I had an El Camino that I turned into a pro str. Now i don't know how big of a motor your running nor the cold cranking amps of your battery. Much less if your alt.is a remainufactured one or brand new. But if your at a 17 someone somehow has overturned the dials a bit and yes it is your regulator you can run all kinds of negative leads to the battery if you have not fried it yet and it won't work it will still overcharge like iys been doing I just can't believe the guy actually today you to run and extra ground wire to the battery but to save you the time and hassle of taking the alt off and taking off the alt.pulley then thefront cover then the wireloome spool just to get to It I'd take it back raise a little hell tell em it fried yer battery too and ask for there super. And see just how fast your problem gets corrected and see if you can't get one of those red top optimum sealed battery's to boot

[BigAL]

Well got the alternator back from Mechman they said it tested out ok and they couldn't find anything wrong with it, so I put it in the car and of course it did the exact same thing and pegged the volt gauge. I decide to take the battery to O'reilly and have them check it out, thinking it might have a bad cell, it checked out ok, so during some reading on the net that I did they said an alternator for a 2003 Escalade which is a 145amp alternator would bolt right into my car, so I picked one up, went home took the Mechman out and installed that one and everything works as it's suppose to and better than what the stock alternator would do, so I'm happy with that. Though I'm still at a wonder, why the stock alternator and the 2003 Escalade alternator work like they are suppose to and don't overcharge, but the Mechman does, and why the Mechman checks out when bench tested, but overcharges when in the car. It really kind of sucks because that Mechman alternator was a clip of money, though the guy at Mechman did say they could put a self exciting regulator in it and that would cure it from doing that. I'm kind of thinking of going that way, and using the alternator on the Monte and just keeping the Escalade alternator in the Camaro since it works like it's suppose to in there.

[dieselgeek]

Did the aftermarket alternator let the car's ECU control the charging like the original GM? Maybe that part isn't working correctly, or possibly someone used the "resistor" trick to fool the alternator into charging full blast all the time, which isn't really a good idea IMO.

[TheSilverBuick]

Did the aftermarket alternator let the car's ECU control the charging like the original GM? Maybe that part isn't working correctly, or possibly someone used the "resistor" trick to fool the alternator into charging full blast all the time, which isn't really a good idea IMO.

I was wondering if the PWM signal curve calibrated in the alternator was some how different than the one the ECU is sending. Never heard of the resistor trick.

[BigAL]

Did the aftermarket alternator let the car's ECU control the charging like the original GM? Maybe that part isn't working correctly, or possibly someone used the "resistor" trick to fool the alternator into charging full blast all the time, which isn't really a good idea IMO.

It only uses the L terminal, my year camaro doesn't have a "sense" wire, so if no sense wire(S Terminal) is used the alternator senses off the B terminal. Thing is the stock alternator I took out didn't over charge and worked, and the Escalade alternator that I have in it now works perfectly like it is suppose to, so I'm figuring that somehow this other alternator that is overcharging isn't sensing the signal from the B Terminal properly or the regulator is just to sensitive to resistance in the system, where the other parts store alternator regulators might be a little more forgiving in that area. Either way the Escalade alternator fixed the low charging problem with the A/C on that the stock alternator had. Though it is still a bit baffling why on their test bench it works properly, but overcharges in my car. And at least the only thing it fried was the headlights, popped those suckers quick.