Funny alternator issue on Jeep
So my winter beater is a 98 Jeep Grand Cherokee ZJ, recently i have been having a strange alternator issue, figured i'd throw this out to you guys and see what you think.
The jeep will start and drive fine, but after a short amount of driving, the battery level on the dash will drop to 0 and the check gauges light comes on. I have an OBD2 HUD that shows battery voltage, so i know it doesn't drop to 0, when this happens the HUD normally shows 11 volts, sometimes drops to the 10's.
So at that point the easy diagnosis is the Alternator, however, this is the odd part, i haven't tested extensively, but it's happened enough times to be more than just a coincidence,.. when i stab it on the highway, the voltage comes back up to 14, the dash doesn't reset and start reading again until i restart the jeep, but i can see the voltage on the HUD. But then when i get back in the city and do stop/go/slow driving, it drops out again.
my theory was worn out brushes on the alternator, but i did a test and just driving around when it happened i tossed it in neutral while still rolling and revved er up to 4 grand which is well beyond highway rpms, and it didn't fix it so engine speed doesn't seem to be the reason it picks back up on the highway.
I have also read things about the PCM and maybe broken joints/traces, as it regulates the alternator power and provides the exciter signal, but that doesn't seem to make any sense with it coming back when i hit the highway.
I did clean up the battery posts/terminals as well and replaced a sketchy looking body ground, but that didn't have any impact.
Just curious if anybody else had any theories.. my plan right now is to replace the alternator and go from there, just curious of any other theories.
Originally Posted by rage2
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