funky charging problem

What kind of car is it?

What is this gauge? Is it an ammeter or a voltmeter? What kind of car is it?

Is there any change in sound when this happens? What kind of car is it?

That makes sense. What kind of car is it?

Okay, take it back to that guy, tell him what happened. He's on the right track. He needs to look at whatever he replaced and see if it has deteriorated. If it has, why? If it hasn't, what else nearby could be loose? What kind of car is it anyway?

--scott

Well, since it is indicating volts, I would have to believe it is a volt meter.

Did you see my second post that was posted a couple hours before your reply?

It's a 96 Jeep Grand Cherokee.

A beep goes off when the warning light comes on, but otherwise no change in sound that I can notice. It isn't a slipping belt, because I can see the pulley turning even when it is failing.

What kind of

It's a 96 Jeep Grand Cherokee.

It's a 96 Jeep Grand Cherokee. One thing I've learned is that Jeep, Dodge, Chrystler use the computer to control the alternator rather than using a voltage regulator. I'm now wondering if the computer is also shutting down the guage on the dash if it detects that it is running at 12V too long, or something weird like that.

Yeah, I took it back to them, again. This is the third time. He said he wouldn't charge for the diagnosis this time. I guess I'll see.

It's a 96 Jeep Grand Cherokee.

Okay, bingo! You need the electrical diagram for the car next, because you need to find the point where the meter is coming off the electrical system.

Since it's a voltmeter rather than a charging meter (and some older cars even have both), and it's dropping to zero, you know that EITHER the point where that meter connects to the electrical system is dropping to zero, OR the ground on the other end is bad. (And if it's a ground, it's a ground used by several things).

Okay, that tells you first of all that you have a voltmeter, and secondly that you should look very careful for grounding issues.

Okay. I'm surprised you can't hear the difference in engine load when it's kicking in, but it may not be very dramatic.

No, I bet the gauge on the dash is good, and I bet it's measuring something on the far side of the bad connection... possibly something that is also feeding the field coil of the alternator.

Something is loose, and my guess is that it's either a ground connection or a bad connector in a cable harness. The problem is finding it, and having the full electrical diagram (which the dealer will have, but most independant shops probably won't unless they are Jeep specialists) is going to be a huge help.

You know that the connection issue is before the point where the meter comes off, which helps narrow things down. But you need the diagram to know where the meter comes off.

--scott

check the grounds to the computer.

I have a friend with a 98 grand jeep cherokee with the same exact issue, did you ever get this resolved? Last Saturday he changed the battery, Mon - Wed....he literally stalls in the freeway....he's freaked out...gauge goes down, light flickers in the dash at times, had him have the Alternator tested and they found nothing.... I'm curious now if the result is the brushes as described..... Please let me us know.....

Thx

I disagree; if that were the case the gauge would drop to battery voltage or slightly lower but would still register voltage. I concur with the other posters that there's a broken wire/loose connection/ something in there that needs to be found.

I suspect that if one were to measure the voltage on the back of the battery when this occurs that you would still read 14V or whatever. checking that would confirm that it's a broken wire.

nate

Not just the voltage on the battery, but also on the back of the Alternator. IT it is showing voltage when the system is failing, then it would bypass the Alternator as being the problem. But then again, it could still be a bad computer.