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Noah930's Avatar
 
Join Date: May 2005
Location: Los Angeles
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Speed Relay

What goes wrong in a speed relay? (The one under the driver's seat?)

I've got an intermittent no-start problem. Seems like it's been traced to the underseat speed relay. But apparently this part is NLA. Is there a way to repair the relay? Anyone got any sources to an extra relay sitting on a shelf somewhere?

Is it the solder joints on the relay breaking? Has anyone ever tried to reheat a relay to reflow the solder and "fix" the problem? Don't laugh. I repaired a faulty Bluetooth circuit board in Mrs. Noah's Acura once by heating it (the board--not the whole car) in an oven. Worked fine for the month we had the car until we sold it.

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1987 Venetian Blue (looks like grey) 930 Coupe
1990 Black 964 C2 Targa
Old 07-25-2014, 03:03 PM
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The only problem I've had with them is the pin contacts stop making consistant contact and then the motor stops... and sometimes at the worst time possible.
The thing is obsolete and dangerous.

Some people just remove it and the car is happy and everything works better than before. It's the factory rev limiter that disconnects the fuel pump relay grounds all at once around 7200rpm.
If you put in MSD 6AL or switch to EFI engine management you get a much better soft rev limiter that works with the ignition and is adjustable.
Old 07-25-2014, 05:30 PM
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So what happens if I just bypass the relay? (And keep on running the stock ignition/FI?) I just lose the protective properties of cutting off electricity to the fuel pumps at 7200 rpm? Does that somehow also bypass the overboost sensor in the engine compartment as well? Doesn't the waste gate also protect against (over)detonation?
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1987 Venetian Blue (looks like grey) 930 Coupe
1990 Black 964 C2 Targa

Last edited by Noah930; 07-25-2014 at 09:19 PM..
Old 07-25-2014, 09:16 PM
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Quote:
Originally Posted by Noah930 View Post
What goes wrong in a speed relay?

Is it the solder joints on the relay breaking? Has anyone ever tried to reheat a relay to reflow the solder and "fix" the problem? Don't laugh. I repaired a faulty Bluetooth circuit board in Mrs. Noah's Acura once by heating it (the board--not the whole car) in an oven. Worked fine for the month we had the car until we sold it.
Re-flowing, huh? Interesting technique, I suppose. Might fry temperature sensitive components, though.
Me - after cleaning the pin contacts and socket and making sure everything fit tight; still to no avail - I just re-soldered every point that I could get to on the circuit board. Fixed the problem.
To your earlier question (IIRC) if you bypass it you won't loose your overboost circuit. And as Jim pointed out, it's just an overengineered rev limiter.
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Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 07-26-2014, 05:40 AM
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This won't fix the problem, but may help get around it.
Blue wires are jumpers to bypass problem devices.

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Bill
1988 Carrera - 3.6 engine (with ITBs, COPs, MS3X) and a whole set of turbo body panels waiting in the attic.
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Memories: '68 912, '72 911T, '80 911SC, '84 911, '85 930, '86 930, '87 911
Old 07-26-2014, 06:22 AM
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Thought I would bump this thread to give Bill's leg a most deserving hump for creating and posting that excellent, easy to read fuel system electronic diagram (complete with how to bypass each component).

I'm having a Paul of a time trying to figure out why my car's engine will only run for a short bit before shutting down on its own (have thrown many parts at it, and done all the usual tests, to no avail), so I basically need to start over, and following this drawing will really help. Thanks, Bill!
Old 09-20-2016, 08:22 PM
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its usually the solder joints that go bad.
you can pull it out and just resolder all the joints.

I removed my speed relay but I put in an MSD box with a rev limiter. trust me, you want a rev limiter. I pulled out one day and went side ways and was bouncing off the rev limiter before I new it. (I did NOT spin). had to keep it there because if I lifted I would have gone around.
the main reason I removed it is because I have the euro CIS and that let me remove the last electronic crap in the car. makes it more reliable.
the MSD is also adjustable. I keep it turned down just a little for extra safety for the engine.

oh, when I removed the speed relay I went into the connector and soldered wired to pins 1 and 2 to the same pin. if you remove the speed relay you can no longer use the O2 sensor. it also controls when it goes to open loop mode which is around 3k RPM.
I suppose you could unplug the O2 and solder the 2 wires together that put it in open loop mode.
either 9 and 11 or 9 and 12
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Old 09-21-2016, 04:18 AM
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I was blown away by the diagram you had and would love to get more. Let me know if still available. I have a 1981 930.
Old 10-11-2016, 03:18 PM
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Yeah, that's a really nice schematic. I'd love to have one for my 81 as well.
I think he drew that for himself and later shared with the group. I noticed in his sig. that he used to have a 85 as well as an 86 so, maybe he drew one for it as well. Perhaps one of us should PM him and see. I believe the 85 would be the same as our 81s.
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81 Pacific Blue 930 Euro coupe slicktop on a strict diet, Rarlyl8 headers, Blowzilla turbo, Tial waste gate, Full bay I/C, Home made center out exhaust, Leask WUR, MSD 6AL, PLX wideband
Wevo shifter, LSD. Next up, Cams, Heads and port work
Old 10-11-2016, 06:30 PM
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Bill is the ultimate king of wiring diagrams, no doubt. Been one hell of a resource for us, myself included.
Those diagrams are pretty accurate for most our our later 930 years. May be some little changes along the way, but generally they're about as good as it gets. Kudos, Bill.
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Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 10-11-2016, 07:45 PM
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Thanks guys.
With a bit of help from another Pelican (Tremelune), a bunch of useful files can be downloaded from links in this post.
As far as I am aware, the basic engine wiring for '85 and earlier cars is very similar to the the '86 wiring but without the emissions devices and associated wiring ... ignore the red parts in this diagram.

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Bill
1988 Carrera - 3.6 engine (with ITBs, COPs, MS3X) and a whole set of turbo body panels waiting in the attic.
Day job ... www.sspowdercoat.com.au
Memories: '68 912, '72 911T, '80 911SC, '84 911, '85 930, '86 930, '87 911
Old 10-12-2016, 03:57 PM
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