Charging Problems

[jhv48]

Here's the problem: Normally, my ammeter gauge registers about an eighth of an inch to the positive side while driving. When the car is off, the needle will rest on the left corner of the zero mark. Yesterday, while driving on the freeway, I noticed the ammeter would behave normally then suddenly move to the off position. The engine continued to run normally. The needle would stay there for a few minutes and then jump to about a quarter inch on the positive side and then slowly drop back to 1/8" on the positive side (normal). Bumps didn't seem to effect the on/off cycle at all. It seems to be doing this at random. I checked the ground wires and the connecting wire. All seems good. Am I just experiencing a failing alternator or is there a wiring problem I should concern myself with.

I've got a Roush 427SR engine with the stock Powermaster one wire chrome alternator. If I need to replace it, which one do I get? Is #170781 the correct one? I have a grooved serpentine belt and replacement alternators seem to all have v-belt pulleys. Do I just swap pulleys with the one I have now? Also, what amp rating is the one that comes with these engines. I don't want to take it off until I have a replacement.

[347stroker]

Jim the ammeter may be bad. Mine was and was causing charging problems. I had it replaced with a voltmeter. If you don't have one get Blas's wiring diagram it's worth it. The ammeter is part of the charging circuit. They are 50'amp gauges. If you are forcing 90 amps through them they malfunction. Tom

[jhv48]

I thought about the gauge going bad, but the fact that when the gauge goes positive again, it goes higher than normal and then slowly falls back to normal charging levels is what I would expect if the engine was running off only the battery for a short time, thus causing the alternator to put more of a charge into the battery to make up for the discharge while it was powering the engine.
If the gauge was bad, I would expect it to return to the normal charging level
once the gauge started working again. Also, when I turn on the fan with the engine running during normal operating conditions, the gauge will make a big jump to the minus side and then quickly return to the zero position as the alternator delivers more charge to compensate for the higher amp drain. When the gauge is showing zero charge at running speeds and I turn on the fans, it immediately drops to about half the negative side and stays there. That indicates to me that the fans and the engine are both running off of the battery, and the alternator hasn't kicked on to counteract the discharge.

[347stroker]

Mine would show a large negative with the lights on then slowly come back to zero. Check the ammeter connections but IMHO put in a voltmeter to prevent future problems. Taking your alternator to a good rebuild shop and have them test it. The chain auto stores usually don't have the proper machine to do the test. Also your battery may be junk. Good luck Tom.

[menace1]

Hi Jim, + 2 on a volt meter to replace the amp meter. I replaced my powermaster alternator last year as the bearing was going out. Also a few months before that the eye connector broke at the post of the alt. as the factory connector is very weak.
Check that infamous ground connector under the the trunk carpet as it's another weak point in the system.

[vatdevil]

Highly recommend converting to a voltmeter.

[diverrick]

If you'll get a volt/ohm meter, try looking at the field wire at the alternator, and seeing if it is following the same as the gauge. If it is, you have a regulator issue, if it is not doing the same thing, then it is either the gauge or the alternator, Next check the output of the alternator.
Alternators don't usually work one moment and then not the next. The either stop working altogether or get low voltage due to a bad Diode.
You can also use a jumper across from the battery to the field, which should give you full unregulated power. That'll show if the alternator is working properly.

[jhv48]

All good responses.

I agree a volt meter is probably a good idea instead of the ammeter. And the connector wire to the alternator did break a couple of years ago. But for right now I am going to focus on the ground wires. I found that the ground wire that attaches to the remote firewall solenoid was corroded. Cleaned and reattached it. The battery and gauge connections were all checked. Alternator connection was tight. Will see if that did it in a few days.

[jhv48]

As a follow up. Problem persisted after checking all the wires and grounds. I Assumed that the problem was a failing voltage regulator. Unfortunately my regulator is inside the alternator. I ordered a new one wire alternator from summit. When I installed it, the old serpentine belt wouldn't fit. Wtf? Pulled the alternator off again and found that Roush installed a half inch smaller pulley on the alternators for their engines. Swapped pulleys with the new one and so far, charging is back to normal. For those of you with Roush engines, the alternator is a powermaster one wire chrome part number 17294-114. 100 amps.

[madmaxx]

Did you check the ground wire in trunk? Pull up carpet behind battery box. Look at terminal where it connects to frame. Mine failed right there and was hard to see until I removed neg battery lead to inspect. Blas led me to the solution

[jhv48]

Second thing I checked.

[Mr Jody]

Thanks for the follow up. Just out of curiosity, are you going to have the old one checked out to determine more definitively what the problem was (and share the knowledge here)? If it’s something simple, you may want to get it fixed (or make your own repair) and have a spare.

[jhv48]

That's exactly what I plan to do. So I'll have a spare in case this happens again.