Charging problem

[la2lvtom]

So I'm having a charging issue with my P5. I have a high output altenator and to it I have the stock charging wire which goes to the brain plus I have a 4 guage wire which goes from the altenator directly to the battery. With a voltmeter attached to the battery, at idle the charge is at 12.5 volts but if I rev up the motor it shoots up to 15 volts but as soon as the idle goes back down the voltage goes back to 12.5. If I disconnect the 4 guage wire from the battery the voltage drops to 12.3 and when reving the motor it stays at 12.3 so that is telling me the factoring set up is not charging. I've heard it might be the PCV (purge/charge valve) is bad but the dealer wont hook it up to the computer because I have an aftermarket altenator and they told me to bring the car back when I have the factory one back on, both dealers in town told me the same thing. Anyone with electrical knowledge of the P5 have any ideas? Any help would be appreciated. Tom

[mmiiimp5]

To me it sounds like the way the alternator was designed. do you have a spec sheet on the alternator? by that you could find out what its outputs are at what rpm. also you could have got a bunk alternator. Is it possible to put an undersized pully on the alternator so it can compensate more rmps at the alternator when your at ide?

[la2lvtom]

I've had the altenator on for about 8 months now, it was built at Ohio Generator (they strictly build altenators for sound competition vehicles). It does have a smaller diameter pully and it specs out at 186 amps at 3200 rpm, when the 4 guage wire (from the altenator) is removed from the battery and a volt meter is attached to the wire it shows about 13 volts at idle and goes up as the rpm's do but at the battery (without the 4 guage wire just factory charging wire) it sits at 12.3 no matter what (possibly just the battery voltage) which tells me the altenator is charging but something in line on the factory wire is not allowing the charge to get to the battery. So possibly the pcm or maybe the fusible link? The 100 amp blow fuse at the side of the fuse box was blown but I replaced it and still no charging.

[Guvner]

First off you need to rule out the alternator as the problem. Forget the wires coming off the alternator, you need to check the voltage directly off the alternator at idle, it should be 13-15v, thats the factory spec. If that proves to be OK then you need to move futher along the line, now since you seem to have the factory charging wire and a 4g wire both going to the battery this might confuse some of us, so without seeing how you have this setup it might be hard to diagnose past this point. But anyways going to the battery with the car on disconnect the positive wires, measure the voltage off the factory wire and the 4g wire you have installed, both should match the voltage off the alternator. If the factory wire shows less then you need to trace back towards the alternator to what the problem is. Next check the battery with the car turned off, should be 12.4v min any less and its likely the battery is dying and should be load tested at your local parts store.