Overcharging

I am having an issue with my '91. I see an almost constant overcharge situation now. It hovers around 16-16.9V which is just into the red zone on the gauge. It is worse when the engine is cold, but only settles to just under the red zone when warm. The volt reading comes not only from the high gauge but also from the volt meter in my CB radio.
I have yet to see an error code in the ECM, though I have noticed a popping sound in my sub amp couple of times when the voltages is at its highest (which is a great test to see how fast one can shut down a stereo system!).

I do have a bearing whine coming from the front of the motor at idle. To be honest I don't know if it's the water pump (HESCO unit), the power steering pump (relatively new), the idler (again relatively new), or the alternator. It is inaudible at start up but gets louder when the engine warms.

A recent alt. test showed "normal diode function" though we saw a big voltage draw, then spike from somewhere in the system (it was an "on vehicle" test) where the voltage when from about 11.5 to 16.9 in an instant.
I wasn't sure if some of the electrical problems I have been having of late were due to a faulty battery. The problems were mostly related to what seemed like low voltage when the engine wasn't running (door locks not working well, dim lights etc.).

I replaced the battery today and cleaned the battery cables. The low voltage stuff seems improved but I still see the high volt condition remain.

I guess the next step is to R&R the alt. and hope it's a switching problem, but what's the chance this is in the ECM?
Will finishing up my Mobi-Arc/Powermaster welder take care of the charging problem if it is the ECM since it assumes control of the charging system?

I hate electrical probs. Spent half the day fighting with the security system as it went into a no-start mode for some reason. I hope it's to do with the charging problem at this point.

Thanks,
Bones :skull1:

It certainly sounds like overcharging. At 16 volts, it will kill the battery. When I had this problem before it was caused by a bad voltage regulator. This was long before the regulators were integrated with the alternator so we just replaced the regulator. I wasn't aware that the ECM was in control of the charging on XJs but my newest one is an '89 and I've not had problems with over-voltage. You do need to fix it before it kills your new battery.

I just fixed this problem in my 91 xj.

Mine would only give me a code when it was very cold outside. It also made the engine run weird, it was probably messing with a sensor or two.

Just replaced the alternator, I gained access when I removed the battery, and moved an AC line aside. It went smooth.

BTW this condition kills your battery real quick. I would have both your alternator and battery bench tested.

Auto zone will test them for free, and the rebuilt Alternator is very nice, plus you will have the core in your hands. Check the terminals carefully to see that the new alternator is exactly the same.

Hope this helps.

it sounds like it IS (like others have said) probably a bad alternator

BUT

i would check all wire connections/conditions going to and from the alternator before you go replaceit, just to be sure

(it would suck to throw a new alt. in there and have it do the same things)

for what its worth (from my experience, anyway) a bad + or - lead on the alternator COULD cause crazy voltage in the system AND over time kill the alternator

check the small stuff first!

HTH

CaptTrev

Well I replaced the Alt and cleaned up the grounds under the hood.

Benefits were better than expected.

The Alt was the source of the bearing whine, and at least partly responsible for the charging problem.
Cleaning up the grounds not only helped the charging troubles, but has straightened out some of the other electrical troubles as well.

Thanks guys!

Bones :skull1:

New to forums so sorry in advance if i break any protocol im unaware of. So i just bought a 93 xj 4.0 with a automatic transmission and now im having a overcharging issue, everytime i floor it the idiot gauge just about pegs to 19, normally it will settle back down after a few seconds and go back to 13.7. One day it pegged after i floored it and stayed there so i cranked the heat turned on the lights to drop the voltage a little and limped it home. Grabbed the ol meter and sure enough battery was at 17.6. I ran to oreillys they hooked it up and said the battery came back good, alternator came back good and its a bad voltage regulator. Id rather not replace my pcm if i dont have to so im hoping someone has an idea as to what this can be. Also i let it sit for a while came back out and then everything was back to working normally but again when i floor it my battery goes up to about 18.

The ECM monitors and controls the alternator's field voltage, to maintain the correct charging voltage..
If the ECM "sees" too low a voltage, it increase the field's voltage.
If the ECM is using a voltage source that has a poor connection(s), and it sees low voltage, it will increase the field's voltage higher than what is normal, leading to excessive voltage.
Before replacing anything, cleaning all the grounds and plugs, that lead to the ECM, is suggested.
The schematic, in the FSM, for your year XJ, is a great help in determining what connections and grounds to clean.

So i have gone through most of my grounds but i dont see how they would be the issue if it only overcharges when i have my foot to the floor?

Actually, that would be a good indicator of a bad ground or at least bad wiring. When you floor it, you can spin up more amperage which will allow the voltage to bridge a bigger or dirtier gap.

Thank you for the quick response and for clarifying. Im just worried it may be the pcm because I park it for a couple of hours and the problem goes away, if i try to drive it right away after it overcharges the gauge and voltmeter still shows around 18....

Well i talked my neighborhood parts store into letting me "try" a pcm. Wasnt the problem. Looks like ill be trying to track down a FSM and finish going through all my grounds. Just replaced the battery today as well
Guy before put in one that was oversized and near to hitting the hood. Thanks for the help and ill be sure to let you guys know what the problem is when i track it down

http://cruiser54.com/

Start at the top. It's renix based but the grounds are in the same place.

Thanks a ton. You just saved me countless hour's and quiet a few bottles of advil.

Well i went over all my grounds. New eyes on all cables and took steel wool to everything, still doing the same thing. Replaced battery cables as well. Any other ideas?

Alternator. Have them bench test it and not just on the car.

Guess that will be my project for tomorrow. Guy i bought it from said he replaced it but ive gotten a couple bad ones out of the box before

Guess that will be my project tomorrow
Would have done it earlier but the guy i got it from said he just replaced it. Ive gotten a couple bad ones out of tye box so hopefully thats it.

If the dashboard charging gauge shows 19 volts, there is almost always a connectivity issue such as, poor grounds, loose/corroded/dirty wire connections, internally corroded cables, loose/corroded battery lugs and/or posts. Load Test the battery. Battery posts and lugs should be a bright light gray color not dark gray or black from corrosion. Cooper cables should be copper color, not green or black from corrosion.

If the dashboard charging gauge shows 9 volts there is almost always an alternator issue, usually worn out/sticky brushes. Load test the alternator.

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One of the two smaller posts was broken on the new alternator the last owner put in. Replaced and problem is gone. Thanks for the replies and help everyone