Volt gauge reading 18v on '91-'96 cluster +other gauge issues while off.

Hey all.

For several days, spaced over a couple weeks, I've been cleaning grounds and tightening cables trying to figure out why my gauge on my 94 Sport is reading 18+ volts.

Today I drove it up to Advance and had them put the meter on it.

We checked it off, checked it running, with no accessories, and with AC on max/high, high beams on.

It read 14.59 running under no load, and 14.3 with everything on. So I have two questions.

One, is any part of the Jeep actually getting 18v? i.e. is it possible the gauge is reading 18v and the PCM is reducing it before it gets to the battery?

Two, any proposed fixes such as cleaning contacts, checking grounds or anything?

Any ideas are appreciated. :repair:

Also, here is a pic of my gauges with the Heep NOT RUNNING, key removed.
Notice the temp and oil pressure are not at 0...

the ECU actually regulates the field circuit into the alternator based on system voltage to regulate it's output. It cannot "reduce" the output once it's generated.

The volt meters in the dash are notoriously poor in these vehicles. I'd buy an inexpensive aftermarket volt gauge and install it directly from the battery (with a fuse) and wait for the next 18V episode. Compare the two gauges to determine if there really is any problem with the charging system or a faulty gauge in the dash.

Thanks Shorty.

The next 18v episode is every time I drive it. HAHA.

My dash gauge was reading 18 the entire time the guy at Advance was checking/reading 14.5v. Also, I typoed my original on-load reading.
It was 14.59 off load, and
it was 14.53, not 14.3, on load.

I'm seriously considering all aftermarket gauges because the factory ones (and the lighting) suck IMO. I'm going to research some options.

I think the gauges are designed to come to rest more or less where they stopped, rather than all zeroing out when power is off.

As Shorty says, these gauges are pretty notorious for inaccuracy. You have a couple of choices here.

One is simply to measure the real voltage, look at what the gauge says, and remember this. All you really need the gauge for is to observe unwanted changes, so it doesn't really matter what the numbers are.

Another choice is to take the gauge apart and recalibrate it. The calibration of these gauges is very primitive. There's a little magnet stuck on with glue. You can adjust the reading by unsticking it and regluing it. It's been a while since I did this, but as I recall, the magnet is stuck to the moving needle assembly, and how high or low it sits on that varies the reading. When I bought a junkyard cluster for my 95, the voltmeter was way off because the magnet had come unstuck. I took it out and reglued the magnet with Shoe Goo, which is very sticky but flexible enough to allow last minute adjustment. Hooked it to a 12 volt source, and nudged the magnet until it was right, then let the glue set. It read accurately for years.

If I have time tomorrow and the weather allows, I'll go out to my now retired 95 and see if I can get a closer look to refresh my memory on this.

Thanks Matthew. It's good to know I can just recalibrate the gauge, and that the gauges don't zero when off. I'm debating custom gauge lighting, and that would be a good time to play with the magnet adjustment. I may look into this depending on which way I go.

Shorty elaborated in my build thread that if I didn't need the lighter I could use that circuit as a switchable source for an aftermarket voltmeter, and that's a good idea too, because sure as anything I'd forget to switch that off and kill the battery otherwise.

Since 4.0s aren't sensitive engines, I don't think I need that +/- 0.10 accuracy that aftermarket gauges bring... ESPECIALLY since my gas gauge drops at least 1/8 of a tank around turns, causing the gas light to come on intermittently from 1/4-tank-on. That should be slosh/float related, so an aftermarket fuel gauge would probably be a waste of money.

I think I might just continue to observe the unwanted changes for now, and proceed with getting a spare cluster from the JY and modding the lighting and calibrating the factory volt gauge. +maybe adding an aftermarket voltmeter. Thanks guys.

I misremembered exactly where the glued-in magnet is placed. Here (if imageshack behaves) I will put a picture of the voltmeter removed from the cluster. You will see a blob of glue. The magnet is stuck to the inside of the steel shell of the meter, and calibration is by sliding it front to back. Since it's magnetic, it sticks lightly to the shell, and you can experiment a bit with placement before gluing it.