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Voltage Gauge Spike

co_big_cheese

NAXJA Forum User
Searched and found a few other similar posts, but nobody posted if it fixed it.

http://www.naxja.org/forum/showthread.php?t=958477&highlight=battery+gauge

Basically, I'll be driving and the voltage gauge will spike to 19. The Check gauges light will come on. Sometimes it will correct itself, but not always. Generally if I shut it off, it won't start. I get nothing, no gauges, etc... clock resets. Sometimes I was able to get it back by shifting into neutral, drive and back to park. All the sudden the gauges would come back.

I can usually jump start it to get it going again. Yesterday, I pulled the battery cables and cleaned the terminals, and it fired right up. Drove it around, re-started it. No problem. Got 1/2 way to work this morning (4 miles) and the gauge spiked again. Shut it off at work. No start.

In other posts people have speculated about the alternator/voltage regulator or a ground problem. I'm assuming I should check the ground first as it's easier. Is it located in the same place as a CJ with the 4.2 (passenger side motor mount?).

Cables look OK. Replace? Pull the alternator and have it checked, or can someone check it without having to pull it?

2000 XJ Sport
112,000

Battery is maybe 2 years old? Cables & alternator have never been replaced.
 
Well, I tried starting it after lunch, no dice. I went to go pull the negative cable like I did yesterday and heard a faint "click". I immediately tried starting it and it fired right up.

Talked it over with a mechanic here at work and we decided to try replacing the battery cable ends. He cut them off and put on what he called "the good ones". They were a crimp style. He didn't really recommend using the ones they sell at AutoZone or Napa. The cables definitely had some corrosion inside, but nothing that I thought was overly bad.

I'll give it a few days and see if the problem comes back. It was happening pretty regularly so I should know soon.

Figured cables were a logical place to start based on the symptoms, and they are cheaper than an alternator. I may run by AutoZone and see about getting the alternator & battery checked tomorrow regardless.
 
Good start.

The main grounds should be three - one from the battery to the fender liner, one from the battery to the engine block (above and behind distributor, or where the distributor should be if you have DIS) and one from the driver's side rear of the cylinder head to the firewall. Check and clean all three.

Your mechanic is correct about crimp-on jobs being "the good ones" - if you seal them after crimping, they'll usually last quite well. I just don't use them because I find that termination using ring lugs is easier (both for service and for logistics) and it's easier to attach multiple cables terminated with ring lugs to a binding post-type battery clamp than it is to crimp two or three 1AWG cables into a crimp sleeve!

Your regulator will be in the PCM/SBEC/ECU/whatever ChryCo calls it, and therefore separate from the alternator. You may want to check and clean the connections on the back of the alternator (three or four in number - if there's a fourth one, it's a direct ground. Two are for the field, and one is the battery output post.) These don't usually get corroded - but they can damn sure get dirty, and that's just as bad. An emery board will suffice for anything that leaves the lug salvageable (just don't use your G/F's and put it back...) A nail buffer board works very well for a final cleaning - I keep both in my toolbox for just these reasons. (I keep a number of strange things in my toolbox, and they're all useful.)

You may also find it useful to clean the lug on the PDC end of the battery-to-PDC cable, and make sure the alternator connection into the PDC is clean as well (it could be either a funky quick-connect going into the bottom, or it could be a ring lug on the end of a section of fusible link wire. Even odds. If it's a ring, handle the same way you handle the other rings.)

If the engine ground is soaked with oil, use some carburettor cleaner on it first to blow the loose oil off before you use anything abrasive to clean down to bare metal - or you'll load up your abrasive in no time at all!
 
Thanks for the reply. I'll see how this "fix" works, but will definitely be checking the grounds and stuff you mentioned. The engine bay was pretty messy a while back thanks to a leaky oil filter housing, but I fixed that and I'll make sure everything down there is good and clean.
 
co_big_cheese said:
Well, it's been 2 days. No problems since replacing the battery cable ends. Hopefully that was it.

You would be amazed at both the number and variety of electrical problems I've traced back to shonky grounds in the engine bay or on the chassis. Grounding to painted metal may make some small economic sense to the beancounters, but makes no sense from a mechanical point of view - paint don't conduct electricity well...
 
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