NO CHARGE ABOVE 4K RPM??

TW0 · Dec 23, 2004

I just bought a completely stock 91 police coupe, since I've bought it whenever I rev the car through the gears to 4k or above the volt meter drops to 9-10 volts and the battery light comes on. Can't imagine this is normal? I've put a fresh belt on and all the pully's spin freely, the tensioner seems to have plenty of tension on the belt, I'm not sure what it could be. any suggestions? Thanks.

HISSIN50 · Dec 23, 2004

might take it out and have it bench tested or load tested in the car. diode might have gone south.

good luck.

HISSIN50 · Dec 23, 2004

oh yeah, what is your static voltage, voltage at idle and at 2K rpm?

good luck.

TW0 · Dec 24, 2004

Without the car running the battery has 12.7 volts, with it idling it has 14.3 volts, same when revving up to probably 3k but when you really rev it you can see the voltage drop down to 12 volts or so, not sure of revs cause I'm under the hood. Any ideas?

Ourobos · Dec 24, 2004

Check your ground strap to the back of the head. Make sure it's there and isn't frayed.

89CopCoupe · Dec 24, 2004

You need an alternator, unless you know how to rebuild the one you have ...

Stang951 · Dec 24, 2004

Or it could be that the alternator is the original Police Unit and is designed to charge like that.
I know for a fact that some police car alts were designed to drop charge at high RPM. I don't remember why, but I was told to get my alt configured the same way a few years ago.

Check with your local electrical shop (not Autozone) to have it checked properly.

89CopCoupe · Dec 25, 2004

Stang951 said:
Or it could be that the alternator is the original Police Unit and is designed to charge like that.
I know for a fact that some police car alts were designed to drop charge at high RPM. I don't remember why, but I was told to get my alt configured the same way a few years ago.

Check with your local electrical shop (not Autozone) to have it checked properly.

So you are saying that some cop cars (like mine) had a special circuit installed to break ignition voltage to the alternator at higher r's? ..... and because of this horsepower saving circuit, cops had the luxury of staring at amp lights as they went from ticket to ticket ..................... cool ................ just tell people you 'got' a factory shift light

Brushes in the alt are worn (revolutions) .... the springs that load/hold the brushes onto the commentator rings are too compressed (time/age/force) ... the commentator rings are worn (revolutions) ... the voltage regulator is tu

blastit116 · Dec 25, 2004

i have a 93 fhp and it dosnt do that so you should probly take it to a eletrical shop

Stang951 · Dec 26, 2004

OK I guess I need to explain that one better (nust've been drunk when I posted). I was told a few years ago (like 8-10) that some Interceptor alts were designed to charge opposite of personal vehicle alts. i.e. they would have full charge at idle and taper off at higer rpm's. Not below normal, but less than normal. If I remember correctly it was because at idle it would keep the car running and power all of the emergency vehicle equipment (lights, cameras, radio, etc). I had a problem with my Camaro charging well and was told I should look into getting my alt reworked to charge the same way.

Hope that clarifies things a little.....didn't mean to sound like an idiot there.

89CopCoupe · Dec 27, 2004

Stang951 said:
OK I guess I need to explain that one better (nust've been drunk when I posted). I was told a few years ago (like 8-10) that some Interceptor alts were designed to charge opposite of personal vehicle alts. i.e. they would have full charge at idle and taper off at higer rpm's. Not below normal, but less than normal. If I remember correctly it was because at idle it would keep the car running and power all of the emergency vehicle equipment (lights, cameras, radio, etc). I had a problem with my Camaro charging well and was told I should look into getting my alt reworked to charge the same way.

Hope that clarifies things a little.....didn't mean to sound like an idiot there.

From what I've acquired, cop cars came with a larger case, higher amp (150ish) alternator ... I think a Leece Neville? At idle they could produce more amps as required of them compared to the 75amp Motorcraft units put in consumer models.

I don't know if the regulators on these monster units were set-up to lower the field as gross output started to increase

SWYZ721 · Dec 27, 2004

That's exactly what it is, traffic patrol vehicles spend more time idling than anything else and it is a reverse wound alt. high charge at low rpm low charge at high, due to all the electronics in the vehicle (video screen, camera, computer, radio, spotlight, light bar)

NO CHARGE ABOVE 4K RPM??

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