Help! This can't be good

[WoodyHank]

Tonight I drove to the dog park (15 m RT) then went to get gas for Woody. He was running low (in his mind), probably 9ish gallons left (at which point he 'runs out of gas', so I was pushing my luck. Got gas, drove home, ran in for about 5 minutes, went to start him again and he wouldn't quite turn over. Tried several times, the cranking, trying to start sound, but just not quite engaging. So I stopped for a minute or so, tried a couple of times again, I heard a noise--maybe a backfire?--and then he started, but when I started driving him, the ammeter, which has been fine, was way over in the positive range, near orange, and after 1/2 mile when it didn't go back do center, but kept moving from + to - I pulled off the road to see what would happen, ammeter kept jerking (it has never done that) so I came back home. I have an mechanic's appt for Monday (compression test, fuel sender, timing chain,general check), but now it looks like I have something new to add to the list. if it quits raining long enough, ammeter is getting fixed tomorrow. ANY ideas what the problem might be would totally be appreciated...I was supposed to leave for my roadtrip next week :( thanks!!! Lisa & Woody Hank

[ October 17, 2003, 10:25 PM: Message edited by: WoodyHank ]

[PlasticBoob]

Hmmm... I don't exactly know what the problem would be on a newer FSJ, but, I would bypass that ammeter ASAP! High in the + range means that the alternator is charging, but if it stays high in the + range, a meltdown may be imminent. If it is moving from + to -, it could be the voltage regulator on the alternator??? :confused:

[Chevelleguy]

With all the cranking, your alternator is having to work extra hard. I would charge the battery before going on. BTW, your rig doesn't have a timing belt.

[Joe Guilbeau]

The ammeter is a guage that monitors the charge rate that the Alternator applies to the battery.

When it goes into the positive range it is an indication that the voltage regulator on the alternator thinks that the battery charge is insufficient and supplies charging current. The voltage that it is reading is falling below the 12-volt-something that the regulator is set for, and it tells the alternator to start putting a charge on the battery pronto!

But then the amp gauge goes negative, which is an indication that the voltage regulator thinks that the battery charge is now suddenly sufficient and therefore is not charging the battery. So the gauge reads negative, which is telling you that the battery is discharging to supply whatever current needed.

The magnitudes of the neg/pos swings indicate the amount of current being supplied to the battery by the alternator or discharged from the battery.

Most likely the alternators regultor is going bonkers and is failing, hopefully this is the culprit.

A more nasty reason could be an intermittent short, where a wire is grounding and discharging great ammounts of current to ground, which the alternator sees as a negative swing, and then the intermitent ground clears up and the regulator picks up the lower battery voltage and provides charging current to bring it back into specification.

Either way, it is a bad situation.

[WoodyHank]

Okay, bad situation, not good. The ammeter was supposed to be bypassed this week, but it's been pouring sheets of rain here every day. The ammeter has been dead on perfect though, no real fluctuations, so I took the advice of someone here and figured it was working for now, fix it ASAP, but don't panic. Till tonight. So about that nastier wire...can that be fixed? and how? Woody has been running great, except for a couple of little quirks.
Oh, and I meant timing chain. I was in the depths of FJS despair and panic (alternating between the two, good thing I don't have an ammeter smile.gif

[WoodyHank]

Follow up: I went and started Woody. Piece of cake, started right up. Now I understand that love/hate thing.

[JeepBountyHunter]

LOL...
and just to say I'm certain what the other's said about it being the voltage regulator inside your alternator is probably correct, had that happen to me, but of course I didn't have an ammeter...fortunately..
-Aaron

Originally posted by WoodyHank:
Follow up: I went and started Woody. Piece of cake, started right up. Now I understand that love/hate thing.

[Max Power]

Once the charge wire from the alternator got too close to the header, the insulation melted off and every time I'd hit a bump or make a sharp turn, the wire would short on the header, the ammeter would jump and the jeep would sorta 'hitch'. at least it was an easy fix.

good luck,
Robert

[WoodyHank]

well, I found out this a.m. that it really helps if the battery cables are both connected tightly, too...the ammeter is getting fixed right now, I'm getting my first round of dirty fingers on the keyboard, but at least I'm learning something!!! thanks everyone!