Flickering headlights and spiking voltage.

[Chin13]

Ok, so I have been having this problem for about a week now and cannot figure out what is causing it. It usually happens within the first ten minutes of starting up then goes away. I am getting flickering headlights, dash lights and a few times my voltage would jump up to 19 volts for a few seconds then go back down. It is not happening consistently so it is making it very difficult to troubleshoot. So far I replaced the headlight switch which I found during searching which can cause the flickering lights but the voltage spike I can not trace down what is causing that. The head light switch did not fix it and I also checked all the grounds and the all checked good. The alternator is about a year old but I also know that the voltage is regulated by the pcm. I am hoping that someone has had a similar problem or know of other things to check. In case it is not in my profile I have a 2000 Jeep Cherokee with the 4.0L. Thanks

 

[Tim_MN]

....voltage would jump up to 19 volts for a few seconds then go back down. It is not happening consistently so it is making it very difficult to troubleshoot.

I would suspect wiring or wire connection issues. How did you check the grounds ?

Perform routine maintenance of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Copper wires should be copper color, not black or green. Do the same for the grounding wires from the starter to engine block, the ground wires at the coil, and the ground wires from the battery and engine to the Jeep's frame/body. You must remove, wire brush, and clean until shiny the cable/wire ends and whatever they bolt to.
Jeeps do not tolerate low voltage, bad connections, or poor grounds.

Test the alternator and inspect the brushes. Just because it is new or newer, does not mean it was rebuilt correctly or is functioning correctly.

 

[Anak]

My flickering headlights went away when I re-did my battery cables. That was step one in a plan to add relays for the headlights. I still haven't gotten past step one, but the problem seems to have been solved.

I didn't notice any voltage jumps, so it may or may not relate to your problem.

Advice to check wiring is a good place to start.

 

[Chin13]

So to add more, I have already replaced all battery and the ground strap about a year ago. I removed, cleaned and checked the ohm reading with my meter at each ground. Still trying to figure out what this problem could be. Voltage spikes then drops back to normal after a few seconds. I might have to start digging into the wire diagrams to start checking everything.

 

[yossarian19]

Voltage spike suggests one of two things to me : regulator had intermittent problem OR the grounding wire from ECM to alternator is intermittently finding chassis ground. The ECM varies the ground to control voltage output of the alt. More ground, more output. If that wire made it's way onto chassis ground, you'd see a big-ass voltage spike.
In the old school, you'd manually apply full ground to the alternator to check what it's output was *then*. The notion was that you had an external voltage regulator that might be bad, so you could see if the problem was the control circuit or the output circuit real easy by manually "full fielding" the alternator. Nowdays, I'm told you can fry components by doing this. At 14.4 volts you pass a safe amount of current through the computer & engine management, at 19 volts you might fry something. So we don't manually ground the alt anymore...
Anyway. I'd follow the wire from ECM to ALT (the plug, not the heavy stuff) and look for any chafe spots.

 

[Hippie Metal]

Watching this thread. Having the same problem

 

[MrAnderson]

the other day my voltage spiked to 19 and then went away. found that if i flipped my offroad lights on it'd reset my stereo and trigger the meter spike. I found my amp wire had become bulbous with corrsion so i hacked it off, put it back together, cleaned my connections, gave the terminals a good scraping and sprayed some of that red anti corrsion stuff on it. hasnt done it since