rmcrom

I am having a problem with my '96 Cherokee. When my RPMs rise to 3000 or higher, my Cherokee's electrical system rises to ~18-19V. When I drop RPM, the voltage drops back to normal operating voltage. I know it is not a bad gauge reading because when it goes into over-voltage condition, the A/C blower fans turn into jet engines and the light behind the gauge cluster turns into a spotlight.

So far, I have cleaned both battery terminal posts. Cleaned the positive battery cable terminal and replaced the ground terminal. I also checked all ground and alternator cables to ensure they are snug. Where should I go from here for troubleshooting?

Jimbo Slice

Bad voltage regulator.

rmcrom

Is there a way to test the voltage regulator? Something else I discovered today is it will only over volt when the engine is warm.

s346k

mine had this issue. replacing the battery cables and several others was the fix. I believe a combo of poor grounds and gratuitous corrosion was the culprit.

BlueRidgeMark

Yep. Start here. It probably needs to be done anyway.


And save yourself some money. Get custom battery cables made by www.bestboatwire.com. Go 4 gauge on the main battery cables and 6 gauge on the secondaries (ground to body and positive to PDC). It's a nice upgrade from factory without being ridiculous (like using 1 gauge). I like getting the clear heat shrink on the ends so that I can see if corrosion ever gets started.


Then go to Amazon for military battery terminal connectors.

I just did this on mine and it is NICE. Easy project, too. Much cheaper than the guys here who sell kits, too. Nothing against them, but $$ is $$.

Jimbo Slice

The sparkys have spoken...

I'd look at new cables.

Willys55

Always good to upgrade cables and terminals, but have the alternator tested with the proper equipment....I'm sure you will find the internal regulator is failing.
Have the battery tested as well, after all they work together as a team.

Jimbo Slice

I believe the voltage regulator on that year is on the PCM. If it turns out to be the issue the only way to fix it is to replace the PCM or install an external, aftermarket voltage regulator.

Willys55

I believe you are correct, I had G.cherokee on the brain.

rmcrom

Thanks for the suggestions. I will try replacing the battery cables and see if that fixes it. I really hope it is not an ECU problem.

BlueRidgeMark

That sounds serious!

Is there a cure?

jordan96xj

Probably not a bad ECU/Voltage Regulator, but instead the ECU "thinks" the system voltage is lower than it should be so it is allowing more system voltage than it should. This probably goes back to bad connections, bad grounds, bad cables, clamps, corrosion.

Willys55

Trail rides are the only cure....

rmcrom

I have the cables on order, but while waiting I've been checking out some more stuff.

I did some checks for continuity with ground on the field wires. I disconnected the wires from the back of the alternator and also unplugged them from the ECU. I checked for continuity between each of the field wires coming out of the molded rubber connector at the alternator end and used the alternator case for ground. The green wire did not have continuity, but the green/orange did. It seems like neither should be grounded, but a schematic shows that the green/orange wire also goes to the ignition coil and injectors. Is this grounded wire a problem or is it normal with something to do with the coil/injectors?

rmcrom

Thought I had found a bad connection, but once warmed up the problem came back.