Recently replaced a dead alternator in my 2002 Ta. I never paid attention before, but now when I come to a stop, the battery gauge moves a little bit. It never gets below halfway (13) but it will fluctuate back and forth a little bit. Is this normal? I have no electronics other than an aftermarket Kenwood head unit. I do have a cam, if that makes a difference.

 

Only time I've ever seen mine fluctuate normally at idle is if some sort of accessory is cutting on (such as the fans), but then it's just a quick dip and recovery....no pulsing. When I did once see pulsing, it was time for a new alternator.

Don't know how big your cam is, but unless the idle is extremely unstable the cam should have nothing to do with this.

 

Thank you for the informative reply. Cam is the Futral Motor Sports FM13 (230 232) Ive never seen anything like this before myself. Any idea what accessory would be causing it do that?

 

I think I have the same thing as the OP, as long as I've owned the car anytime I hit the brakes when under 1k RPM I will see a quick dip down to almost 13 volt (on the gauge) and at different points over the last year I've replaced both the Battery (old one wasn't putting out half it CCA's when tested) and the Alternator that died on me one day while I was at lunch.

I've also done the BIG 3 upgrade with 0 gauge which helped a little bit (I get a higher voltage at first when cold then before), from what I've read the next thing to try is to go around and clean all the contact points for all the grounds under the hood.

 

That cam isn't wild, so I imagine with a good custom tune the idle should be pretty stable. As such (and assuming a solid tune with a relatively stable idle), I don't think it's cam related.

Is the fluctuation a constant pulse, or just an occasional dip and recovery? If the former, then it's probably the internal voltage regulator on it's way out, or some other internal alternator issue. If the latter, then it might be something as simple as the fans cutting on and off, which, depending on your tuning and cooling system, might be happening more frequently than would be normal for a stock car that has stock fan settings.

The cooling fans are about the only thing that would cycle on and off on their own and create a noticeable fluctuation on the volt meter at idle. Another less likely possibility would be an A/C compressor that is low on freon, and is cycling on and off while you have the AC/Defroster on....compressor clutch engagement/disengagement would cause a small voltage dip and recovery.

 

How much is the needle bouncing around? Hook up a scanner (if you have one) and watch what voltage the PCM is seeing. The factory gauge isn't exactly accurate. A bouncing voltage can be a bad or failing voltage regulator.

 

This is the case.