ibmike150

I have a 99 Cherokee 4.0 and it's been having some strange electrical issues. I will get a spike in voltage that pins the voltmeter. The Jeep runs fine except sometimes I need to manually downshift (automatic).

I replaced the alternator and cleaned up a few of the ground contacts as well as added a new ground battery terminal and cable from battery to body.

I lost my fuel gauge and speedo yesterday but sometimes they will jump around along with the rest of the cluster or everything just dies although the Jeep will continue to run.

Not sure where the voltage regulator is, I've read it's in the PCM. Is that the box with the fuses and relays in it or the electrical system on the drivers side.

Any ideas as to what the issues could be?

Potatowalker

I'm sure someone will correct me if I'm wrong, but I think the voltage regulator is a part of the actual alternator. The PCM is the box next to the airbox on the driver side fender well with 3 plugs coming out of it. There is a TCM for the tranny shift points behind the glovebox somewhere usually.

Have you measured the voltage at the battery when the gauge starts giving you problems? I know in my 96XJ the volt meter in the gauge cluster liked to make up it's own readings at random and often read way higher than the actual system was operating under. I measured at the battery terminals with a voltmeter with it running and with it off and it always read normal even when the gauge in the dash cluster said like 18volts or higher. The tranny shifting issues could be old fluid or something else unrelated. I dont trust the volt meter in the dash in my 99 either because so many people have had the actual gauge or the wiring harness for the gauge cluster give them false readings. I'd verify the problem if you haven't yet, before you buy any more parts (unless of course it needs them anyway)!

Since you had a bunch of separate gauges go out at once, it almost sounds to me like the gauge cluster wiring or something like that...

Turbo X_J

The cluster connector is defective, there is a retrofit available from the dealer.

salad

The alternator is only internally-regulated on Renix models, everything else the VR is in the PCM.

I'd agree that a connector refresh is in order before doing much else. Disassemble, clean, grease, and reassemble the connectors on the PCM and the instrument cluster. Electrical contact cleaner, and a nylon or light brass wire brush would be good for this. For lubricant/sealant I recommend a conductive electrical grease like Gardner Bender OX-GARD or San-Chem NO-OX-ID Special A. You can use dielectric grease around the edge of a connector but, as it is an insulator, not on the actual pins themselves.

DFlintstone

I'm nearly worthless on a 99. Yes, the current to the alt rotor (the strength of the electro-magnet spinning inside the stator) , is controlled by the PCM. Pre 91 it's in the alt. Spiking high.. Maybe the pcm is seeing low voltage and so "ordering" more voltage.

'The PCM is the box next to the airbox on the driver side fender well with 3 plugs coming out of it.'


I'da' kept my mouth shut here, but high, pegged? Serously got to wonder if the PCM is "seeing" the true system voltage, as said, cleaning all the connectors, and some dielectric grease, (unless you plan to put it into orbit)(private joke), cleaning the pcm connectors makes sense to me. Happy new Year!

Klaatu55

Seems strange and totally unrelated,but isolating TPS from heat and later changing it seems to have cleared it for me.

DFlintstone

The ground circuits on thees things might be goofy, for a reason. It might be some ground's, ground back through the computer. (to THAT stud) Maybe to protect a bunch of sensors and sensitive stuff from "perturbations" from the ground side.

Cleaning the connection to ground by your dip-stick mount can't hurt.

Maybe allot of supper important stuff grounds there. Idk.

ibmike150

Thanks for the input and Happy New Year! I will get some electrical contact cleaner and dielectric grease and clean up all the grounds and contacts again.

ibmike150

Update: cleaned the ground connected to engine block, same results. I know the voltage regulator rarely goes bad but is there any way to test if it is the reg?

Turbo X_J

You should have a constant ~ 13.8 v at the battery with the engine running, and all accessories on. Do you notice a difference in illumination when the dash mounted voltage gauge goes haywire headlights flickering, etc?

CCKen

FYI, here's some photos of the ground locations in the engine bay of a 1999 XJ with notations as to what circuits are grounded at the locations.

ibmike150

Yes the lights gauge flicker and dim. Fuel and Speedo no longer work but sometimes fuel will go from E to F and than die back down. Occasionally all the gauges will die out and other times she will run at 14 volts (on the dash gauge) just fine.

Thank you for the photos, I believe I missed the single ground on the block, will do that tomorrow.

ibmike150

I noticed that there is a wire that a previous owner has added to the PCM, does anyone have a diagram of the PCM pins and what each wire is?

sean21

This sounds odd. But my gauges were dead for the longest time. Sometimes they would jump around like yours. I tried every trick related to dead gauges. What it ended up being was the fuse for the horn in the fuse panel on the passenger side. Pulled the horn fuse and the problem was gone. Don't know why. But no more gauge issues. No horn but that's ok with me.

ibmike150

Maybe bad insulation or connections on the horn circuitry in your case, i'll try it for grins.