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tuf-924 · Joined: 05 Nov 2009 Posts: 119 Location: wollongong

Hey guys I have been having loads of problems with my charge from my alternator I actually recently got a reconditioned alternator 2 weeks ago upgraded from 90 amps to 120 amps, still unusual charge rate, It charges at 13.6 but once the engine heats up it drops to 11.5 and when I turn the car off it don't want to start again. Anyone ever had this happen before?[/img]
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Jakkq · Joined: 29 Sep 2008 Posts: 810 Location: Omaha, Nebraska

It sounds like a bad alternator to me! Is there a reulator on the back of the alternator at all?

Have you attempted any other tests with it?
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1979 Porsche 924- Snailshell
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scriblz7 · Joined: 07 Dec 2008 Posts: 112 Location: kirkland WA.

make sure there is a good ground strap from the alternator, it sits on rubber bushes so isnt grounded to the engine without the strap. my voltmeter read 11.5 without the ground strap.
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Riley
79 924 n/a with gt body
15 VW GTI

ronafios · Joined: 14 Jun 2011 Posts: 26 Location: Canberra, Australia

It's also worth checking what's happening with the positive lead - it is in a location very close to the manifold and the shielding can disintegrate. In most cars it seems to loop from the back of the alternator to the + terminal on the starter, and then back to the battery. I had a lot of alternator frustration until I discovered the cabling issue. It was inside a heat shield tube, and when removed, hundreds of bits of plastic fell out (what remained of the plastic wire shielding).

I took the alternator in to a local auto electrician to bench test, and when he gave me the OK, that's when I played with cabling.
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BionicBalls · Joined: 05 Jan 2009 Posts: 642 Location: Charlotte, NC

tuf, Do you have a 924 or a 924S?

If it is a 924 then, I was under the impression that 90 amps was the highest output you could get from a Bosch unit.

If it is a 924S then yes 120 is available. If this is the case then the alternator does not have rubber mounts and grounds to the bracket and the wiring does not come near the exhaust.

What you do mean by warms up, as in how long? Are we talking about minutes or seconds? Are you testing the voltage the entire time? When exactly does it drop?
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1980 924 NA
1982 931

flosho · Posted: Fri Jan 27, 2012 5:43 am Post subject:

I second the idea to check to make sure you have a solid ground!

I actually drove my car for over a year without a ground strap without real symptoms of a problem and ended up having to R&R the alternator a couple times because I was unaware of the ground strap that was missing..
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