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Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Does it have one? What is the behavior? Would it be the "BAP BAP BAP BAP BAP" we all know and love, or a longer shutdown?

(yes, my new motor has finally seen 6k+)
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

morghen · Joined: 21 Jan 2005 Posts: 9102 Location: Romania

it happend to me once...it was a longer shutdown...if it werent for the seatbelt i would have had tasted the steering wheel as i was in first gear

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fiat22turbo · Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR

So its more a fuel cut-out. Interesting. I'm guessing it hits around 6500RPM?

My non-Porsche turbo car does this when the boost level spikes too high or you hit the rev limiter, it is terrifying the first time it happens and yes you do feel as though you'll be eating steering wheel

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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Morghen, that is exactly what happened, and I probably would have hit the wheel if not belted.

Either a fuel cutout or a ignition kill that took a moment to reset. It was around 6300 RPM, and I am trying to decide if it is a pump power supply problem.

Think I'll run the pump from a secondary relay, since the battery is inches away from it now.

Thanks for the replies, and other ideas still welcomed.
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Smoothie · Posted: Wed Apr 13, 2011 7:37 am Post subject:

The other possible cause is a torn wg diaphragm, and triggering of the overboost cutout switch. Both this and overreving result in fuel cutoff for 931s that were delivered with cats and o2 sensors.
RoW cars could and did use the rev-limiting rotor to cut ignition instead for overrev protection.

Cat-equipped cars (US, etc.) got the pricey $90+ fp relay with overrev sensing and fp cutout built in.
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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

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Interesting info, Smoothie, thanks. So the DME relay must have a solid state component that kills the fuel pump power on overrev.

FWIW, I have no overboost switch, and my WG doesn't have a torn diaphragm, because it looks like this:

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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

morghen · Joined: 21 Jan 2005 Posts: 9102 Location: Romania

i think you can still get overboost even without a torn WG diaphragm.
my car is ROW and apart from the fact that it does not use one of those relays you guys have...at the moment i had that engine shutdown experience i was runing a normal 12V relay instead of the fuel pump relay. So the over-rev or boost cut off must have been comanded by the DITC.
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jazz guy · Joined: 26 Nov 2002 Posts: 434 Location: Colorado

Rasta, I am not the ultimate authority on this but I am quite certain that as Smoothie stated, our US cars have a fuel cutoff rev limiter through the relay... and when it kicks in under boost, it hits HARD. It's definitely not a soft limiter where the revs stay up, gently bouncing off the limit, like newer vehicles.

When I purchased my 931, a college buddy of mine had an identical silver and black '82... We spent some time tracking the rev limiter down because my car would slam into the limit at just over 6100 rpm. This definitely put a damper on the fun factor. So we, I should say HE (he was finishing his master's deg. in EE), traced it back to the relay, tore the relay apart, and tweaked it to raise my rev limit. It's been 25 years ago, so I'm not positive, but I don't think it's totally a solid state circuit that controls it. I think I remember him talking about a mechanical spring in there... but again, that was a looong time ago...

Smoothie · Posted: Thu Apr 14, 2011 1:23 am Post subject:

My Geocities pics from then are long gone, but here's the link to where the various 924-931 fp relays were discussed - http://www.924board.org/viewtopic.php?t=10360

Quite a lot of electronic components are packed in there (the 931 rev-limiting relay) including 2 circuit boards, 2 timer ICs and a potentiometer or variable resistor which we guessed was the adjustment for the rev limit.
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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

RC · Joined: 25 Mar 2007 Posts: 2637 Location: Australia

Pity your pics are gone Smoothie, and not archived in cyberspace either. Do you not still have the originals to upload elsewhere?

This relay definitely needs some modifications or throwing in the trash. Are you guys crazy, 6100, 6300 maybe? F that!

Sounds like another of Porsche`s tricks to advantage the 911. The pussy relay. Ba ha ha aa ...

Another advantage to running MS, programable ignition or anything else but stock, even a MSD.
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