Rev Limiter (Speed Meter)

[Brian Fuller]

Can I ask a favor of anyone who happens to have a spare rev limiter (aka speed meter)? My 78' SC will not run with the rev limiter connected. The previous owner hot wired the fuel pump so that it would run when the key was turned in the on position. After cleaning up the mess, the problem is traced to the rev limiter.

I could not find anything about how to test the Rev Limiter. My guess is that the two terminal in the pic below should not have any continuity. When you get 7000 rpm, only then should these two have continuity which sends ground to the fuel pump relay and shuts down the FP.

The brown wire is ground, at 7000 RpM the unit sends ground to the brown/red wire which sends ground to the FP and kills the FP.

Please test if there is continuity between the two terminals in the illustration below. If there is no continuity, my Rev Limiter is toast!

Many Thanks,
Brian

[jnberry]

Hi Brian. I have no continuity between those terminals on mine.

[Brian Fuller]

I really appreciate it!! I had a hunch my Rev Limiter was toast.

All the Best,

Brian

[timmy2]

Maybe just install the European type of rev limiting rotor?
Then disconnect the broken US version and you are done.

EDIT: part number is 930-602-901-01 $60....

[boyt911sc]

Jnberry,

Interested to know the six (6) wiring connections for the rev limiter (J35). What are the wire colors for each pin? The Porsche shop manual shows only four (4) wires in the wiring diagram. Thanks.

Tony

[Brian Fuller]

Dennis, my understanding is if you have a CAT, you need to use the Rev limiter that will kill fuel.

Tony,
It is a six prong connector but only four wires. Below is a diagram of the colors and the terminals where they connect:

Brown/Red . Brown

Red and . Red/White

The car runs great without the Rev Limiter, just think I should get this buttoned up some day as this is a safety feature.


.

[timmy2]

Re the CAT:
That explains why it is listed as a Turbo part for the US cars in the US PET.
My ROW '78 never had the electronic rev limiter or a CAT.

[Walt Fricke]

Timmy's suggestion is the simplest - get one of the limiters which goes into the distributor. You can pretty much set those where you want them by bending the tab which holds one end of their spring this way or that - out is higher limit, in is lower. Of course, if you can get one in the flavor you want, that's the simplest.

It isn't much of a safety feature, though. It only helps if you get a stuck throttle in neutral or with the clutch in. Above 7,000 RPM the engine starts getting asthmatic, and it won't spin up a lot farther. Certainly not before you can do something about it, like turn the key off.

It won't save you from the money shift, alas. And when in gear with the accelerator working normally, I don't think you can directly damage the motor because it is going to run out of breath and you will realize from the extra noise and the fall off in acceleration that you should upshift.

[boyt911sc]

Originally Posted by Brian Fuller

Dennis, my understanding is if you have a CAT, you need to use the Rev limiter that will kill fuel.

Tony,
It is a six prong connector but only four wires. Below is a diagram of the colors and the terminals where they connect:

Brown/Red . Brown

Red and . Red/White

The car runs great without the Rev Limiter, just think I should get this buttoned up some day as this is a safety feature.


.

Brian and JNBerry,

Thanks for the information. My '78 SC is parked for the winter at my son's house and have to remove the left most gauge to access the rev limiter. Do you have any information to share about the continuity between these pins? Just curious. Thanks.

1 ~ 2
2 ~ 4
3 ~ 4

Tony

[Brian Fuller]

Tony,
All I know for sure is that the brown/red and brown wire leads should not have continuity. Since I have a failed unit, I can’t speculate as to the rest. If you take the plastic cover off the unit you will note that at least one terminal (the red one) is coupled with the terminal above it. I can’t remember what else I saw when I was in there.

The red/white wire is from the Tach and at 7000 RPM the unit works by closing the circuit of the two ground wires; sending ground to the FP relay.

[T77911S]

not sure why you need a rev limiter just because you have a CAT( catalytic converter?).

that's not the 930 rev limiter for the 86+ US cars.

rotor rev limiter has to be "Set" each time you replace it.

you can replace the CD with an MSD with a built in adjustable rev limiter. that's what I put in my 930 when I removed the stock rev limiter because of reliability.

[Brian Fuller]

To summarize some of the posts I reviewed (see links below) Cutting ignition by using a rev limiter 'rotor' on the distributor would dump unburned fuel into the cat. That, combined with the air injection could damage the CAT and the reason why the Porsche engineers designed the rev limiter to cut fuel. Cutting fuel flow ensures this won't happen. I'm depending on the information from these posts mentioned. If I can get away with using a rev limiting rotor, that would be great.

79SC rev limiter?

Rev Limiter Rotor

911 SC 3.0 Rev limiter

Rev limiter recommendations???

[jnberry]

Originally Posted by boyt911sc

Jnberry,

Interested to know the six (6) wiring connections for the rev limiter (J35). What are the wire colors for each pin? The Porsche shop manual shows only four (4) wires in the wiring diagram. Thanks.

Tony

See the following photo (and schematic under the controller). BRN/RED called out, as it's a little hard to distinguish from the brown ground. Hope this helps.

[jnberry]

Originally Posted by boyt911sc

Brian and JNBerry,

Thanks for the information. My '78 SC is parked for the winter at my son's house and have to remove the left most gauge to access the rev limiter. Do you have any information to share about the continuity between these pins? Just curious. Thanks.

1 ~ 2
2 ~ 4
3 ~ 4

Tony

Tony, I get the following:

1 ~ 2: Continuity
2 ~ 4: NO Continuity
3 ~ 4: NO Continuity