Brynjaminjones

For several years now I've been having voltage problems with our '97 ZJ 4.0.
It's fine when driving, but as soon as the engine speed drops, the charging system can't keep up. This is of course worse in winter when I've got the headlights, heater and heated seats going at the same time.

When I come to a stop the voltage drops down to just above the red, but sometimes it will then go all the way to zero, chime and pop the "Check Gauges" light on. Using the rear demister will do this nearly every time.
If I turn the accessories all off, the voltage will usually recover.

When moving it's mostly fine. If I'm driving at highway speeds (higher RPM) I can use all the accessories with no issue at all.

Giving the battery a full charge doesn't help at all. The alternator was new two years ago. It marginally improved the problem but not by much.


The other issue (probably related) is that you can see the lights kind of "flickering" at idle. They're not turning on and off, more like pulsating brighter then dimmer a couple of times per second. It's most noticeable looking at the radio or the license plate lights.

Has anyone else had similar?

97grand4.0

time to go to autozone and have them check the alternator

Brynjaminjones

Unfortunately I'm in the UK - that's a service that isn't so easy to find over here!

97grand4.0

Ah. Right. Well then my focus would be squarely on the alternator or charging circuit. You mention heated seats, that suggests to me
that you have the larger ampacity alternator which I forget exactly which one that is. I do know the chime and check light
coming on is a signal that the PCM is sensing too low of a voltage. Jeep made these with just enough alternator to support the factory installed options. Any new lighting, etc, will overwhelm the alternator and set the chime off. You may also notice the idle dropping at stops as this occurs. Not good. Could stall even. I suspect at one time the alternator may have been replaced and instead of spending the extra for the right alternator they fitted it with the 90A alternator which is the least, most basic version. It's what mine came with and
I installed bright headlights and experience the same voltage dip and stops if I run the heater and fog lights the same time.
Absent that the only other thing that comes to mind, that I have not experienced or seen, is that it may be possible the voltage regulator, which resides in the PCM itself, is malfunctioning. There is no replacement for the voltage regulator, you must replace the entire PCM unit. But I have never seen this to be the case and still suspect the alternator being either defective diode or simply undersized.
Let us hear back how you make out.
This is why some sort of a test would help, but, it still may not be definitive as to the exact cause or even which part, pcm or alternator. I do however think most testers would show a bad diode.

Good luck

taylor martin

I had the same issue after installing fog and off-road lights, Voltage went to zero even with a six-month-old battery at full charge. Simply do what I ended up doing, switch to a 110-volt alternator and all should be well. I wish you luck dude.

alijawas

HI

I fitted bright headlights and noticed that if I operate the heater and fog lights at the same time, the power drops and stops.
Absent that, the only other thing that comes to me, which I haven't seen or experienced, is that the voltage regulator, which is housed inside the PCM itself, may be failing. The voltage regulator is not replaceable; you must replace the complete PCM device. But I've never seen this before, and I continue to believe the alternator is either malfunctioning or inadequate.
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