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MunkPuppy

I made the mistake of shifting into 3rd instead of 5th, during a high-acceleration run. The engine died until it dropped below 6000rpm. Thankfully I had already released the clutch, so the engine resumed running and spinning down. I've run a few checks on my engine, and it seems just fine.
WHEW!

I've seen it asked if the 931 has a rev limiter built in... as you can see, the answer seems to be yes.

Incidentally, I don't recommend that anyone attempt to verify this information, unless you have a fresh engine that you are planning to install very soon

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'80 931 FOR SALE

"It's a shame that stupidity isn't painful"
-Anton Szandor LaVey

Hugo · Posted: Sun Apr 11, 2004 7:50 pm Post subject:

Seems to me you have been saved by your boost pressure sensor. Your turbo is warped to extreme speeds by your wrong change of gears. and knowing my own driving style you probably never toke your foot of the gas, so mayor overpressure caused the sensor to break contact, and your fuel pump was shut off, so it dropped in rpm until you took you foot of the gas. anyway thats my guess. never heard of a rpm limitter on a 924 turbo, when your car is at the end of it's max rpm. it can't run any faster because of the setup of the rest what's build on the engine, tubes, fuel dizzy, turbo, fuel lines, injectors, etc etc.

Smoothie · Posted: Mon Apr 12, 2004 12:25 am Post subject:

We looked into this pretty thoroughly a couple months ago -
http://www.924board.org/viewtopic.php?t=10360
http://www.924board.org/viewtopic.php?t=10331
http://www.924board.org/viewtopic.php?t=8997&postdays=0&postorder=asc&start=46

931's made with catalytic converters and o2 sensors have the rev limiter built into the fuel pump relay and ROW cars have it built into the distributor rotor.
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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

Hugo · Posted: Mon Apr 12, 2004 1:17 am Post subject:

Well I have a '79 euro turbo, without cat conv. or 02 sensor, and mine doesn't have a rev limitter on the rotor, how do you explain that?
Is the us setup different from the euro setup?

Paul · Posted: Mon Apr 12, 2004 1:29 am Post subject:

Maybe you or the PO installed the cheaper rotor sometime in the history of the car?

Hugo · Posted: Mon Apr 12, 2004 3:03 am Post subject:

Not likely it has the TCI-h rotor. wich was standard for this exact year and model in europe. I looked it up on the etka system at my work. and the ignition partnumber matched with the chassis number of my car.

Smoothie · Posted: Mon Apr 12, 2004 4:01 am Post subject:

I'm not familiar with TCI-h and can't say if they have rev limiting built in somewhere else, as in a control unit like on a 928, but my guess would be that you have it provided in one way or another - just not good to not have it.
In any case, the overboost cutoff would only be activated if there were a problem with the wastegate, as in torn wastegate diaphragm, split control line to it, valve in wastegate stuck closed, or if some added-on wastegate control was set so high as to exceed the cutoff switch's limit. As long as the wastegate is funtioning properly, the cutoff switch won't be activated (unless of course if the switch is faulty and activating at a very low pressure).
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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

john h · Posted: Mon Apr 12, 2004 9:37 pm Post subject:

The ROW cars(with digital ignition 81 onwards) have a rev limiter in the control unit.

The USA/Canada and Japan market cars have this as well (supposedly) but also due to the emission controls they also use a relay on the pump cicuit which has a "speed governor" to limit the revs.
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Remember a Porsche is not just for Christmas,

if you take it to pieces slowly it can provide anguish all year long!

MunkPuppy · Posted: Tue Apr 13, 2004 10:14 am Post subject:

my 931 is an 80 with a bypassed boost pressure switch (with the leak in the charge tube it's not needed, and it's dead anyways), and no rev-limiting rotor...
So I'm pretty sure there's a rev limiter in either the fuel pump relay or the Transistor Ignition System...
_________________
'80 931 FOR SALE

"It's a shame that stupidity isn't painful"
-Anton Szandor LaVey

Lizard · Posted: Tue Apr 13, 2004 10:36 am Post subject:

it is in the fuel pump relay,
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3 928s,

CMXXXI · Joined: 05 Nov 2002 Posts: 1939 Location: Vicksburg, MS

Here we go again... y'all didn't re-read the threads that Smoothie referenced. Those using the incredibly expensive fuel pump relay have the rev-limiter built into the relay. The 931's that do not (All ROW, all years), have the rev limiting function built into the distributor rotor, or perhaps into the digital ignition boxes.

If your rotor looks something like this:

It's the rev-limiting type.

Hugo, if yours does not look like the photo above, it isn't the OEM part.
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'79 Eurospec 931

Hugo · Posted: Fri Apr 16, 2004 7:37 am Post subject:

Well Sorry to say, as I said I looked mine up with the Etka system at work, the numbers on the distributor matched, and the rotor (ordered at the local porsche dealer) does not look like your pic. I have the small relais in mine witch could be the wrong one. So it could be that mine was taken out and replaced by a normal 924 relais, I will check the numbers and get back to you

Zuffen · Posted: Sat Apr 17, 2004 2:15 pm Post subject:

That is odd, all the new Porsche rotors I've bought don't look like that. But then maybe they were bought off the 924 number versus the 931 number.

Tom Charlesworth told me years ago that the rev limiter is built into the control unit (series 2) and that it triggered the fuel pump to cutoff on a over boost.

Manifold pressure, manifold charge temp and RPM as well as TP decide the fuel enrichment at high RPM.

In an overboost condition the fuel pump is triggered off. When it comes back on the engine will dump fuel and it makes a nice flame out from the tail pipe. Ask me how I know with a one bar boost.

Dennis has the car now and I wonder if he has ever gotten into it hard.
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Bob Dodd - 924turbo@cox.net
931 1982, 944 1982 euro, 924S 1988SE, 93 968 tip 06 Silver Cayenne S, 06 Black Cayenne S

I have Way too many cars, parts for the 931,944 and 951