924Board.org

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

This is on the 87 924S. I'm posting here because I'm not convinced it's unique to the S, and I want to get some more ideas.

In Jan, the alternator apparently failed. Took it out, had it test, yep, bad. Got a remanufactured B&A from S&G Imports, a fairly reputable foreign parts supplier in Livonia MI. Put it in. The car kept dying while being driven, so I started chasing other things. Long story short, I disconnected the aftermarket radio and fog lights. Does it again. I pulled the relay to the rear defogger. Does it again. Swap out the battery with one known to be good from another running car (81 NA). Does it again.

Take the alt out have it tested. Bad. Go back to S&G, get a replacement unit and install it. This time, before putting it back in service I decide to test things in the garage. Another long story short, if I start the car, then disconnect the negative lead to the battery so that it's running on the alt only, here's what I get.

1. No load, shows 14V
2. Lights on, shows 14V
3. Any combination of other electrical load, voltage decreases incrementally. Under full load, it will go down as fars 7-8V.

This was all at idle. After talking to my dad and Vaughan both, we theorized that maybe the alt need to be at higher revs than idle speed. Now here's the weird part. No load, car running only...increase the idle by pulling on the throttle, and the voltage DROPS at higher rev. WTF! I've never seen that before.

It doesn't make sense to me that a bad ground would cause that. Unless I'm completely confused, increased resistance from bad ground would actually cause the draw to be LESS and should not affect the voltage output of the alt.

It is possible that I've gotten a 2nd bad alternator. This happened to me on the NA (different supplier, different brand). It actually took me THREE TRIES to get a good alt for that car. Before I yank this thing off yet again, is there anything obvious I'm missing? Or am I just unlucky?
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erstwhile owner of just about every 924 variant ever made

Paul · Posted: Sun Mar 16, 2008 6:41 am Post subject:

You're near Detriot, put a GM alternator in there with a proper ground!
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Has this been discussed somewhere? I did a search in 924S using "gm alternator" and haven't found anything yet...how about a linky linky? Or a model?
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erstwhile owner of just about every 924 variant ever made

Paul · Posted: Sun Mar 16, 2008 7:05 am Post subject:

It's been done for a 931, not sure anyone has done it yet for an S.

I'd refrain from unhooking the battery while the car is running.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Paul · Posted: Sun Mar 16, 2008 7:33 am Post subject:

A 924S has ELECTRONIC fuel injection and ignition.

DMEs are expensive.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

bruce76-924 · Joined: 22 Feb 2007 Posts: 105 Location: Bradford, England

Dan,

If your earth is good and your power cable from the alternator to the battery is good, then the alternator is faulty.

At idle with or without load you should read between 12.5 and 14 volts (do not disconnect the battery when running - you can cause big voltage spikes). If you have an inductive amp meter you can also check how much current is flowing into or out of the battery, after start up I would expect a good alternator to be putting about 20 to 30 amps back into the battery.

Have you checked the battery correctly to be sure that it is not at fault, if you have had a run of charging problems then the battery could also be damaged. A quick check for your battery is make sure that the voltage is 12.2 volts or higher and then if so dissable the engine (unplug fuel pump relay) and then crank the engine for 15 seconds. Observe the voltage of the battery whilst cranking the engine, initially it will drop off and then stabilise, once stabilised it should not continue to drop more than 0.3 volts and it should not drop below 9 volts. Once you have stopped cranking the engine it should go back to 12.2 volts. If it does not meet this test it is faulty, no ifs no buts and you should replace it.

Alternator wise, I have come across units where the charge drops off when revving as you describe and it has always been down to a faulty alternator. Hope this is of help.

Cheers, Bruce.
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1976 924 LHD, full cage, semi tube chassis, 951 brakes, lightweight 951 body panels.
1.8t engine conversion with Holset turbo and 6 speed Audi gearbox.

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Thanks guys. Gives me a few more things to try. Looks like I'm going back to S&G. I'll see if they have any suggestions. Any suggestions on where to source a GOOD quality unit for the 924S without paying a fortune? FYI, I have $240 into this particular reman unit that I can get back from S&G if necessary.
_________________
erstwhile owner of just about every 924 variant ever made

Paul · Posted: Sun Mar 16, 2008 7:50 am Post subject:

$125 HERE with a lifetime warranty.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Paul · Posted: Sun Mar 16, 2008 8:36 am Post subject:

They are also called Advance Auto and I have been buying stuff from them since 1992 with very few issues.

The warranty includes towing for 2 years:

CSK Alternator/Starter Roadside Assistance is available 24-hours-a-day, 365-days-a-year, anywhere in the United States and Canada, for two (2) years from the date of purchase of your CSK alternator or starter. To be eligible for reimbursement you MUST call the toll-free 24-hour roadside assistance service number provided to receive roadside assistance. Service is for passenger vehicles, vans and light trucks only. Service includes a jump-start and a tow. This service is provided on a reimbursement basis. You are required to pay the service provider at the time service is rendered and send in for reimbursement. Service is limited to a maximum reimbursement of $60.00 US/$90.00 CN currency.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

Smoothie · Posted: Sun Mar 16, 2008 11:33 am Post subject:

Bench testing the OE Bosch alternator a few years ago, I got very different voltage readings between having the battery connected and having it disconnected - http://www.924board.org/viewtopic.php?t=13272&start=24

At least a few of us have installed Delcos - numbbers, 924 turbo, myself -
http://www.924board.org/viewtopic.php?p=117221#117221
That CS-144 is a 140 Amp alternator. It fixed my low voltage, and short-lived battery problems. It may be what you need to power whatever add-ons that have been added, as well as to push the "juice" through those 20+ year-old wires.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Smoothie, this is the 87 924S, not the NA or 931...
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erstwhile owner of just about every 924 variant ever made

Smoothie · Posted: Sun Mar 16, 2008 11:45 am Post subject:

Yes, I know. -And if I know me, I'd be looking into fitting one to the 924S (if I had one). 140A is almost twice the capacity of the OE Bosch alt.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Ok, just checking.

You know what I might do is check with those guys that do the power pulleys for the 2.5L. They might have a solution for a better / more modern alt. Worth looking into. But I don't think it would be as easy on the 924S to retrofit a delco unit. The alt is basically fixed, and the heim joint on the ac unit is what tensions the belt. So you'd have to find something with exactly the right geometry to fit the exact mounting points and still tuck in nicely under the MAF. Not impossible, but I've got too much on my plate to work on fabbing up stuff for a daily driver, if you know what I mean

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erstwhile owner of just about every 924 variant ever made