dlwilson

iTrader: (1)

I can't figure out why I keep blowing up alternators, and could really use some ideas.

This is a LT1 from a 1996 Caprice police car, with a PCI harness, in a 1991 Jaguar XJS. The police car has a 140 amp alternator. The diode bridge in the original alternator failed, and discharged the battery through the alternator. I replaced it with a used eBay alternator, which failed the same way. On the second alternator I actually caught it happening because the alternator got too hot to touch, but of course it was too late.

Google said it might be that the alternator wasn't grounded well enough, so I put a 4ga cable off the alternator bracket and put in another used eBay alternator. This one worked for a little while, and then stopped charging. Parts store tested it and confirmed it was not charging. Below is ground strap off alternator bracket.




So I finally got smart(er) and bought a new alternator with lifetime warranty. Put it in today and it won't charge. I am stuck. Here is alternator:





The battery is about six months old. Here are some voltage readings:

battery after low battery and trickle charge overnight: 12.51
battery with car running and new alternator: 12.15
battery after car running after 10 minute drive: 11.99
battery with car shut off after test drive: 12.22

Here is a diagram of how the car is wired. Is there something obvious that is wrong with this?

Shownomercy

iTrader: (1)

How do you have the alternator excite lead hooked up?

dlwilson

iTrader: (1)

I don't know. I am using a PSI harness with a connector for the alternator, which you can see in the second picture. I just checked the PSI instructions, and it says there is a single red wire to the alternator. I am not at the garage to confirm.

The connector looks like this:



Is that supposed to go to one of the PCM connectors via the PSI harness?

Wait, wait, wait, I just found this in the PSI instructions:

WARNING: If the Alternator is not charging and you are using a NON-GM Alternator such as a Power Master brand Alternator, you must switch the pin location from L to position F at the Alternator connector on your PSI harness. If you have any questions regarding switch the wire at the Alternator connector, please contact our technical support team via e-mail or direct by phone.

Let me see what PSI says about that.

dlwilson

iTrader: (1)

I went through a couple more alternators, and fooled around with the 470 ohm resistor trick, but couldn't get it to work. Finally I took the advice of PSI tech support, and bought a rebuilt AC Delco alternator, and it just worked.

So don't use off-brand alternators.

Puck

iTrader: (17)

While it seems like your issues may be solved, I can't stress the importance of having good, clean grounds on a modern computer controlled vehicle. Even with your rebuilt alt, measure voltage from neg battery to a chassis point like the strut or frame. Should be under .03v. My SC had old crappy grounds causing charging issues and was all the way up to .05v...I added a 4ga strap from the neg battery terminal to under a strut bolt, then removed and cleaned the factory chassis GND before reinstalling in its stock location near the k-member. Now there is only .01v of "noise" in the shared ground, which fixed an idle charging issue I was having and as a bonus a lot of the buzzing in my radio is gone.

Bad grounds can do all sorts of weird things to your gauges, charging system, and ECU - especially once you start adding aftermarket electronics.