Andre

86 944 na

while driving: voltage gauge reads about 12, and jumps around frequently(sometimes upto 14 then back down to 12) While at 12 all the gauges(ie:rpm, water temp) bounce around.

If i stop and try to start it, a lot of the time it wont start and just click. Then randomely it will start again and everything will be fine and 5 min later voltage problem again.

I replaced the alternator with a rebuilt one and the problem persists. I just went to get the amperage checked and the alternator is giving off 65, its supposed to give off 115. Did i just get a bad rebuild?

what would cause the alternator to give off less amperage?i checked the grounds on the battery and on the block, should i check the started ground, could that cause the voltage problem?

someone PLEASE HELP i'm stuck

Danno

Well, the current drain on the alternator is only in relation to the load. So if all you have is the basic drain going, it shouldn't be that high. Then as you turn on accessories, lighs and stereo, the amperage draw increases. So the lighs are worth about 15 amps. Turn on a big stereo and you can draw anoher 10 amps, etc. Sounds like you might have some sort of a short since 65 amps is an aweful lot of current just for idling a car.

Andre

so is a bad ground a good guess?

also it wasn't at idle, when he checked the amps he reved the car

IceShark

Danno, is right. 65 amps is a lot to be drawing if you don't have many items turned on, though a discharged battery can soak up a bunch.

BTW, your alternator will put out 115 amps at idle if you load it up, you don't need to rev it. Also, your alternator voltage will drop as the amp load increases. Once above about 35 or 40 amp draw, the voltage will start on the downhill slide from the nominal ceiling set by your regulator.

You want to check your grounds then the positive feeds off the battery and alternator. Sounds like a classic case of a poor connection.

Andre

how do i go about finding this poor connection? what am i looking for?a torn wire?a wire thats not attached?

IceShark

You can do it with a multimeter either checking for voltage drops or high resistance.

Or visually looking for corrosion. Scrub off the connectors and terminals with a wire brush to clean, then cover with dielectric grease or vasline. You may also have corrosion between the crimp terminal and the wire, which is tough to see, but a good bet if the wire next to the terminal is corroded. You probably have to replace if that is the case though you could try and see if you could get solder to stick and flow and sort of rehab it.

While you may have problems inside the car, the ones to look at are in the engine bay & at starter.

Danno

I suspect a short somewhere in the wiring harness. That is, a positive+ lead is getting into contact with a ground somewhere (a grounded wire or the body itself). This would explain the high current drain. Also the intermittent nature of the voltage-gauge would seem to indicate a mechanical contact that's sporadic...

What I would do is hook up an amp-meter to the althernator output to measure total current-drain. Then unplug fuses one at a time to see which one restores the current-drain back to normal levels. Then trace the entire path of that circuit to see where the short is sapping your power.

Gerald Allgire

I had this happen when the cells in the battery shorted together. It would come and go just as you described. Car wouldn't start when it would short either. Had it load tested without success. After trying to figure out what was happening, the battery stopped taking a charge at all. I probably wouldn't have found it right away if the battery hadn't finally died. Replaced battery and all was ok.

Dano_944

Bad battery post? I've had this happen on numerous vehicles that I've driven hard on dirt roads in Mexico. Tugs and pulls on the battery wires can lead to weakened battery posts. Very hard to see, but deadly to the electrical system...... and can draw enough current on the alternator to burn it out prematurely. Check your battery carefully..... all parts of it. Cells, posts, body. You'd be amazed at what you'd find on an old battery.

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