hardrock21

iTrader: (6)

I'm having a difficult time figuring this one out. When I first start the car, charging voltage is fine, around 14.5 volts...Slowly as the car warms up to operating temperature the voltage drops down to 12 volts. I have a lot of stereo items so I got rid of the stock alternator, which tested good btw, and bought a brand new Delco 145 amp truck alternator. Installed it with a new 4 gauge wire directly to the battery...same problem still existed. Replaced exciter wire and pigtail, same problem. Another note, if I add loads to the car, like headlights for example, the voltage always jumps about 2 volts above wherever it may be at the time. I thought about running the 12v ignition on switched wire for the exciter with the 470 ohm resistor in-line, but don't want to burn up a brand new alternator. Any ideas? Anyone run into this before? Thanks for the help.

Paul

hardrock21

iTrader: (6)

Also, I have several added ground straps on the car along with the factory ones, so I don't believe grounding is an issue. I also removed my capacitor from my stereo as I've heard of those shorting out internally and causing a short to ground...That seemed to help it and delay the voltage drop a little, but it still happens everytime.

hardrock21

iTrader: (6)

TTT...Trying to figure this out.

hardrock21

iTrader: (6)

BUMP...I started working on this issue again. I bought a new battery to rule that out. So it's got a 145amp Delco alternator w/ overdrive pulley, new battery, New 4 ga power wire directly from battery to alternator....When warm it reads sub 13 volts. I also tried wiring an ignition on exciter wire w/ resistor and didn't change a thing. Any ideas?

hardrock21

iTrader: (6)

I've read until I've gone cross-eyed on this. Everyone says Check battery, alternator, run new power/ground wires, verify all connections. I ran a new wire battery to alternator, but I haven't run one alternator to distribution yet...Someone has to have run into this issue before? Anyone?

wssix99

iTrader: (5)

How are you getting the voltage readings? Are you measuring at the alternator or looking at the dashboard.

If you are looking at the dashboard, then I'd recommend testing at the alt cold and then hot - then test at the battery cold and then hot. That will help rule out a lot of things.

hardrock21

iTrader: (6)

The gauge, also hooked a DVOM to the battery, also logged it w/ my Matco scanner reading it directly off the ECU. It did the same thing by each reading, though the dash gauge does seem to read a little lower then the other 2 methods.

Paul

wssix99

iTrader: (5)

You may have a wiring issue, in which case, the gauge and the ECU methods won't help. They are giving a measure of what your accessories are seeing for voltage and not what each component is doing.

So, are you seeing the voltage drop at the battery with the DVOM when the car is warm?

hardrock21

iTrader: (6)

Yes sir. I'm trying to figure out the exact range that is considered too low. it gets down to around 12.80V when warm at it's lowest point. If I kick on a load, like the headlights, it usually brings it back up to around 13.20, but eventually will drop w/ headlights on to 12.80ish after a while. From what I understand, it should really never spend time below 13V, especially w/ loads on. The ECU reads identically to the DVOM...The gauge however, reads a little on the low side so I dont put much trust in it. Thanks.

Paul

sjsingle1

iTrader: (1)

was the alt NEW ? or rebuilt?

hardrock21

iTrader: (6)

Brand new AC Delco 145 amp.

sjsingle1

iTrader: (1)

reason i say that is soooo few alts are ACTUALLY new.....sure its not a reman?

hardrock21

iTrader: (6)

Ya I got it from a buddy that bought it directly from GM.

wssix99

iTrader: (5)

The battery should read 13+ all the time unless it isn't charging properly. Are you sure your exciter wire/circuit is good? I wonder if its loosing contact when things warm up and expand?

hardrock21

iTrader: (6)

The exciter is doing its job, I forget what the voltage was supposed to be but when I checked it it was energizing like it should. I even ran a new wire from the pinout to the alternator from the ecu pinout. Then I tried running an ignition on wire with resistor directly to it. No matter what I do I get the same results.

hardrock21

iTrader: (6)

I wonder what the chances are of the voltage regulator being shot in the new alternator. Would be highly unlikely since it was new and since the stock alternator was doing the same thing. I've tested both regulators on and off the car. Cold and hot. I'm not sure what else to try to get them to fail.

wssix99

iTrader: (5)

Easy. Just test the voltage at the alternator with the engine cold and then warm.

OK- That's not easy, but it should confirm this or disprove it.

hardrock21

iTrader: (6)

I've done that. I have tested them on the car when the voltage is low and it comes back good diodes, good regulator. Same thing on a repeated bench test. I ran it 5 or 6 times back to back on a bench tester and have been unable thus far to get a failed test on either alternator.

hardrock21

iTrader: (6)

Does anybody know if it is normal to have high resistance between the engine block and positive battery cable when the cables are disconnected from the battery? By high resistance I mean like 9 mega ohms...Is that normal? Any ideas?

hardrock21

iTrader: (6)

I can't consider 9 mega ohms a short, but I honestly expected to get an open circuit reading when I did that test so it caught me off guard.