rev limiting on a 79sc

OldTee · 11-29-2010, 05:16 AM

Where and how is this done? Location?

How can the limit be tested without a grenade to the engine?

Is there a good write up on this subject?

Flat6pac · 11-29-2010, 06:09 AM

The limiter on the US cars is built into the tach.
Bruce

OldTee · 11-29-2010, 06:32 AM

I presume this is the schematic the starts to answer my questions. Thank you for responding, it caused me to pull the book out and look. Always a good way to begin.

Now, what does it mean? Where is J63? What comes from the speedometer G21?

Flat6pac · 11-29-2010, 12:32 PM

The red and white comes from the speedo.. the current flow is from the top of the page to the bottom. The part may be inside the speedo.
Bruce

Kemo · 11-29-2010, 02:46 PM

this is a good topic...cant wait to hear the solution. my rev limiter works. At the last DE I reved it up until the engine cut out (about 7K or so). after 5K rpm, its hard to get the foot off the happy pedal!

I made a concious effort to pay more attention

OldTee · 11-30-2010, 04:44 AM

Ummmm... It was suggested last night that the 78-79 does not have a rev limiter. When the engine quits at high rpm it has reached valve float. Not saying this is correct just need information from somebody that really knows for sure.

OldTee · 11-30-2010, 07:04 PM

Somebody out there has researched this question. Wouldn't it be interesting if a whole generation of 78-9 SC owners thought they had rev limiters but really didn't.

OldTee · 12-02-2010, 07:15 AM

I am trying to understand this schematic. It looks like this is the circuit that cuts the engine off in the event the engine stops running, then fuel is cut off. This circuit does not appear to have anything to do with rev limiting.

If I am wrong tell me how.

Back to the original question: How is rev limited on a 78-79 with CIS? I think Motonic equipped cars are rev limited in the computer.

OldTee · 12-02-2010, 10:41 AM

I have found a reference in Bentley (78-83) to rev limiter switch on page 970-9 but not a location on the location chart later on in the book.

Any hints from somebody who has stripped a 78-79 for parts?

johnsjmc · 12-02-2010, 01:03 PM

The SC uses 2 different rev limiting systems. North American versions use a fuel cut relay. It is located behind the instruments near the drivers side trunk hinge. It cuts the fuel pump power to prevent unburned fuel from being passed into the catalytic convertor. EXcess unburned fuel can damage the convertor. ROW cars us a rev limiting ignition rotor instead.
I have seen a car with the fuel cut relay which would stumble and misfire well below the limiting speed.We disconnected the relay and it ran cleanly to redline so we installed a rev limit rotor available from a turbo instead

OldTee · 12-02-2010, 01:09 PM

Quote:

Originally Posted by johnsjmc

The SC uses 2 different rev limiting systems. North American versions use a fuel cut relay. It is located behind the instruments near the drivers side trunk hinge. It cuts the fuel pump power to prevent unburned fuel from being passed into the catalytic convertor. EXcess unburned fuel can damage the convertor. ROW cars us a rev limiting ignition rotor instead.
I have seen a car with the fuel cut relay which would stumble and misfire well below the limiting speed.We disconnected the relay and it ran cleanly to redline so we installed a rev limit rotor available from a turbo instead

That wouldn't be a 91161713600 would it?

Do you have a pn for the row turbo you referenced?

Thanks

johnsjmc · 01:30 PM

It,s been years . Pelican had the turbo rotor in stock but the ROW SC rotor was going to be a special order. The turbo rotor limits the revs at about 200 RPM higher than the SC (7000 vs 6800)so I didn,t feel it was a problem .You cant use a 2.7 rotor because they are a different size.
Looks like # is 930-602-901-01-m14 The ROW SC special order # is 93060290102

OldTee · 12-05-2010, 02:18 PM

Thanks, this sounds like the straight poop. I've ordered a rotor. Will see how it goes or better, how it interrupts.

OldTee · 12-13-2010, 05:56 AM

Here is what I got from PCA tech. Food for thought!

"The rev limiter is in a box located behind the fuel gauge. I could not find a part number for it, but it may be printed on the box. It has four wires: red, white/red, brown, brown/red. It works by grounding the fuel pump relay. The circuit is part of the 78 wiring diagram in the factory manual. They call it a speed switch. It cannot be adjusted that I know of. It can be disabled, by disconnecting the brown/red wire. I think all cars are the same on this.

Chris Powell"

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by OldTee

Here is what I got from PCA tech. Food for thought!

"The rev limiter is in a box located behind the fuel gauge. I could not find a part number for it, but it may be printed on the box. It has four wires: red, white/red, brown, brown/red. It works by grounding the fuel pump relay. The circuit is part of the 78 wiring diagram in the factory manual. They call it a speed switch. It cannot be adjusted that I know of. It can be disabled, by disconnecting the brown/red wire. I think all cars are the same on this.

Chris Powell"

Chris,

You are correct about this rev limiter for SC's. However, if your go back to you earlier post (wiring diagram) the red/white wire should be connected to the tach instead. Not speedometer!!!! I don't see how a speedometer could stop an over-rev engine during a test!!!!. Any thought about this? Thanks.

Tony