924Board.org

[chuck21401]

I'm looking for a 90A alternator for my 931.

Several posts on this board mention the AL115X. I've seen it listed on these sites as a 90A alternator for the 924 turbo:

FCP Euro 147.49 + 75.00 = 222.49
Paragon Products 180.19 + 35.00 = 215.19

Amazon sells the AL115X but warns me that it does not fit my car.
The price is $214.86 + $12.50 = 227.36

I've also seen the AL325X listed these sites as the 90A alternator that fits my car:

Bosch site/Amazon Bosch store 295.47 + 22.50 core = 317.97
Rock Auto 158.79 + 75.00 core = 233.79
AutoZone 214.99 + 75.00 core = 289.99
Napa 270.99 + 53.96 core = 324.95

Anyone have experience with either of these alternators? I've included the prices since I was looking them up. The shipping rates vary, the vendor on Amazon is free. Some of these core charges are so low that it doesn't make sense to ship the core back.
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1981 Porsche 931 w/S1 engine & euro g31 transaxle. Water-cooled intercooler

[chuck21401]

I bought the AL115X from FCP Euro. Supposedly "guaranteed to fit" and they offer "EZ returns" in case it doesn't work out. I've had good luck with them with other purchases. Will report my findings.
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1981 Porsche 931 w/S1 engine & euro g31 transaxle. Water-cooled intercooler

[chuck21401]

I installed the alternator and a new belt. It was easier than expected.


Old and new part. Just needed to swap over the fan and pulley.



And this plastic part on the back


Also replaced the battery/starter/alternator harness with this part from Kroon Wiring Harnesses. The wiring with the four wire plug was a bit short, so they sent me an extension.
Here's the product: https://www.kroonwireharnesses.com/porsche-924/porsche-924-1980?product_id=897



Installed


Another angle



The new alternator cranks out more volts than the old one at idle and revved up...except when it starts running rough. At that point voltage to the fuel pump fuse drops and the situation spirals down quick.

** UPDATE/EDIT: The problem was not with the wiring, fuse box, etc. The fuel mix was off. I reset the fuel mix and set the idle speed. Works fine now and voltage is where it should be at idle. **


I think my problem is in the relay panel at the fuel pump relay and/or fuse box. Also need to check the ground behind the fuse box. I'm wondering about the red/blue power wire that runs from the battery to the fuel pump relay. The connection at the battery is clean/tight with a new connector...need to crawl under the dash to check the other end.
The overboost switch is grounded but need to check that again too. There's a flaky connection in there somewhere. The fuel pump relay is new.

I'm seeing more than 1V drop from the battery to the fuel pump fuse. When I turn on headlights, fog lights, blower motor, etc....the voltage drops even more and it starts running rough...RPMs drop...voltage drops more. The fuel pump fuse and relay heats up and becomes hot to a touch; the fuel pump does not.

I tested the fuel pressures with the CIS pressure tester...everything seems to be within spec.

I think I've read all of the threads regarding fuel pumps, fuel pump relays, fuel pump fuses and wiring problems. Hopefully I have this electrical gremlin on the run. My first suspect is the connection at the relay housing. My second suspect is the ground for the overboot pressure switch, though if that was not grounded, it seems like the car would not run at all.
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1981 Porsche 931 w/S1 engine & euro g31 transaxle. Water-cooled intercooler