Lobster70
NAXJA Forum User
- Location
- Spokane, WA
I'm here on behalf of my son, who is the proud owner of a 1991 Jeep Cherokee Sport, 4.0L, AT. We have a problem with the electrical system that looked like a bad alternator, but may be something else.
Details:
Tested the alternator while on the car using a load test tool with an alternator test setting. It showed that the alternator was bad. It also showed that the battery is good. It is a "24 month" battery that is 4 years old.
Last night we fully charged the battery and replaced the alternator. To my dismay, there is almost no change in behavior. I tested with a volt meter on the battery terminals just now:
- engine off: 12.59 V
- engine on: 12.0 V
- engine on plus headlights, heater, radio on: 11.5 V
...so, it is not charging like it should. I would expect 13V or so.
One stupid thing I did was fail to have the old alternator tested, but I just called the auto parts store and they still have it. They will test the old one AND the new one when I bring it in. I will update this post after that. However, I have been told that the test off the car is less reliable than when in a running engine.
I know it is possible that the new alternator (a remanufactured unit) is also bad. Assuming both alternators are actually OK, what other component could cause these symptoms?
Other factors that might be important:
My son left his headlights on a few weeks ago. His friends, also 16-year olds, gave him a jump start. Could they have done something wrong that would cause this problem?
Also, the cheap aftermarket stereo that it came with acts up (he will be replacing it) and he is convinced that the stereo receiver is causing this somehow. I'm not.
Any advice will be greatly appreciated. This is my first post here, coming from another forum that is apparently losing members like crazy. I joined there unaware, but have been told
is the place to be.
Eric
Details:
- Engine will start and run, but electrical system is low voltage (dim headlamps, turn signal won't blink, wipers very slow, etc.)
- Gauge on dash shows low voltage (red zone, left side of scale, 8V or something)
- Revving the engine makes no difference in headlight brightness or dash gauge.
Tested the alternator while on the car using a load test tool with an alternator test setting. It showed that the alternator was bad. It also showed that the battery is good. It is a "24 month" battery that is 4 years old.
Last night we fully charged the battery and replaced the alternator. To my dismay, there is almost no change in behavior. I tested with a volt meter on the battery terminals just now:
- engine off: 12.59 V
- engine on: 12.0 V
- engine on plus headlights, heater, radio on: 11.5 V
...so, it is not charging like it should. I would expect 13V or so.
One stupid thing I did was fail to have the old alternator tested, but I just called the auto parts store and they still have it. They will test the old one AND the new one when I bring it in. I will update this post after that. However, I have been told that the test off the car is less reliable than when in a running engine.
I know it is possible that the new alternator (a remanufactured unit) is also bad. Assuming both alternators are actually OK, what other component could cause these symptoms?
Other factors that might be important:
My son left his headlights on a few weeks ago. His friends, also 16-year olds, gave him a jump start. Could they have done something wrong that would cause this problem?
Also, the cheap aftermarket stereo that it came with acts up (he will be replacing it) and he is convinced that the stereo receiver is causing this somehow. I'm not.
Any advice will be greatly appreciated. This is my first post here, coming from another forum that is apparently losing members like crazy. I joined there unaware, but have been told

Eric