Hi guys,

I'm having issues with my 1999 jeep Cherokee. I keep burning my aftermarket H4 bulbs. As far as i can tell its from a voltage spike. They literally will burn out as the voltage spikes.

My headlights, dash lights and blower fan will all ramp up only and if I put my jeep into reverse and give it some rpms. It spikes for a second and then is fine as i continue to drive in reverse. I know it spikes from hearing the blower fan and seeing the headlights and dashlights brighten. The voltage gauge in the dash spikes a little too from 14 to 15/16.

I have searched some other threads and no one has this exact problem of this only happening like this in reverse.

I did replace the alternator a while back. Could this be the problem? The battery seems to be fine. While driving in drive at any rpms the voltage is steady and fine.

If I take the alternator in will they be able to diagnose if its the alternator causing this?

Jeep runs great otherwise, i just need my headlights to work again.

Help meeeeeee.

 

Most the auto parts stores have a machine to test alternators. It maybe something with the voltage regulator inside it.

 

They can also test the complete charging system.

 

If the alternator is under warranty I would change it and see if that will fix it .

 

Thanks for getting back to me guys.

I just went in to check the alternator and the alternator / starter / battery checked out fine.

Again though, this only happens in reverse so they couldnt check the alternator while driving. I dont know if warranty will cover putting in a new alternator because they will test my old one and it will probably test okay.

Im willing to try replacing the alternator just want to make sure i have covered all the other bases.

 

Does it make any sense to you guys that this is only happening in reverse?

 

No. I find that a little perplexing.

One of the reasons voltage can spike is because the voltage regulation is a function of the PCM (computer). If the computer is suffering connectivity issues (such as poor ground connections) it can begin to think it is sensing lower voltage in the system and command the alternator to increase the system voltage.

My only guess is that the reverse lights, or perhaps something in the NSS (neutral safety switch) that controls the reverse lights is fuzzing the system voltage up somehow, or causing a ground that the computer depends on to become compromised.

Have you metered the system voltage at the battery, while someone else shifts into reverse to see what happens to the voltage at that instant? Also, have you inspected the reverse lights during any of this to see if anything obvious is out of sorts, like a dim light, or flickering, or a dead bulb?

 

The only thing I can think that mite have something to do with it would be a loose ground from the battery to the engine . Did you check all the grounds that you can see under the hood .

 

Thanks guys!

I never thought about the NSS or the reverse lights. Ill check the reverse lights.

I am going to check / clean all the grounds now and report back.

I metered the system voltage at idle and with rpms (in park) but not engaged into reverse. I dont have a meter so ill have to do that with a friend soon.

 

Doubt you have long enough cables but i got super long wires for mine and stuck it way up on the windshield for self diagnosing stuff if i dont have a buddy around.