Second computer, 100k alternator, fluctuation in the guage increases with rpm, throws check engine light on the freeway sometimes.
Thoughts?

 

Have you replaced the shut down relay on the drivers side inner fender...it shuts the alternator charge on off really quickly to help maintain constant charge....I think that's how it works? If that relay f starting to go on the fritz , maybe it's causing this issue?

 

Not it. I switched to a manual voltage regulator (mopar) and it did similar. Gotta be the alternator?

 

My truck does the same. It also eats regulators. I go through 2 Naoa's a year. Even when it works though my needle shakes at idle until i give it throttle to go. Ate another regulator tonight on way home in fact. Very irritating.

 

Mine has never thrown a check engine light but it has had the fluctuation with RPM before. For me it ended up being the alternator. I changed it and it did the same thing, I had to go through about 3 or 4 NAPA alternators before I got one that worked as it was supposed to.

 

Sounds like you have at least 1 bad diode in your alternator, missing one phase would cause an unsteady output.

 

Interesting. I had put an alternator on my truck about 6 months ago (Napa) but my needle on volt guage was broke off so I never saw the fluctuation. Fixed the needle about 3 months ago and noticed it. Replaced the regulator about the same time and went through 3 before I got one that worked. Then last night it was all over the place. I didnt think about the alt. May have to warranty that out along the regulator....again.

 

I had one running like that, also hi volts setting output code, did the external regulator, and chased the output wire coupler near the battery as the culprit, losing current from the wire to coupler connection, ran another wire to remedy the output, pcm controlled regulation is not dependable, in my opinion.

 

I thought it might be a diode. No easy way to check that though. I guess it's time to try a replacement (and try to refrain from jump starting anyone!).

 

Just replaced my regulator with a Mopar and guage doesn't shake and it charges at 14.2v. Imagine that. Its unbelievable how many bad regulators I've gotten from Napa.Even the ones I thought were "good" were overcharging. Last one I put in showed 15.2 at idle and I thought that was good. No more Napa's for me.

 

So did the external regulator mod?

 

91.5 have external regs from factory

at idle my gauge goes up and down like crazy. hook a voltmeter and ammeter to the battery and it's fine. 14.1v no fluctuation. i have an new 120A alternator and new mopar BLUE voltage reg.

I gave up, the factory gauge is POS> i hooked up an autometer volt gauge right to the batt. and it sits right at 14

 

My lights are fluctuating with the needle.
I ordered a new Alternator just for good measure.

 

Yeah, my lights were doing the same the other night with the old Napa crap. Hopefully this Mopar one last a while.

 

If your volt meter only bounces at idle and goes away as RPM increases, then it is a resistive voltage supply to the alternator field winding. On 89-91.5, the problem is most likely the ignition switch. On 92-93, probably the auto shut down relay. In both cases, any bad connections will also introduce a resistance causing this symptom.
If the volt meter bounce increases in frequency with an increase in RPM, most likely a bad diode in the alternator.