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mark houghton's Avatar
 
Join Date: Jul 2008
Location: Central Washington State
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That POS relay under the seat....

Just a reminder that if you're having mysterious "she just shut down" or "won't start" symptoms, along with looking at the usual culprits (the yellow relay from hell, the overboost sensor, fuel pump relays....and the like) don't forget that there is the overspeed relay under the drivers seat that ties all this worthless crap together. Mine has been doing the sporadic no start thing, and when fiddling with the relay the pumps would stop...then start...then stop, depending on the position of the relay.

Could be a bad connection (nope, cleaned the piss outa that), could be a bad/broken wire in the bundle (awfully unlikely and equally difficult to find), or could be the relay itself (hopefully not at something like $350).

One more time, I pulled the seat out and took the relay to the workbench to remove the tin and inspect the innards. Looked almost new, no visible oxidation or bad solder joints. But, there are about 8 connection points where the manufacturer used rivets to make electrical connections to tinned metal strips. Unfortunately you can get to only two of them....which I did with some flux and solder to solder those rivets in place. And while had the iron hot, I turned the circuit board over and re-soldered all the remaining points that eventually lead to the socket connection points.

No problems with it since.
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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 07-13-2011, 04:57 PM
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Good explanation on how this works from my brother, I sent him all of my wiring diagrams so I can just call when I have a problem....this was the speed sensor/O2 sensor relay. Both contacts are in same relay, from this thread:

Fuel Pumps not working with Ign.



the drawing i have shows the speed relay or rev limiter side cuts out at 7k, and the other side is for the O2 sensor. it shows it cutting out at 3k.

tim's relay had several broken solder joints. one was on the coil for the FP's. the others where on some of the major pin joints. some even for the O2 side. so for those that have bad relays' pull them apart and just resolder the points i mentined.
you can apply 12v to pin 7 and ground to pin 5 to test the relay. both relays should pull in.
(i actually used a 9v battery)

my explanation to tim on how it worked:
look at the fuel circuit as 2 seperate circuits. one is the 2 FP relays, the yellow relay(contacts), the rev limiter, and the pressure switch. the other circuit is the yellow relay(coil) and the AFM switch.
the AFM switch removes ground from the yellow relay, de-energizing it when the engine is running.
the FP circuit gets its ground through the contacts of the yellow, then the rev limiter then to the pressure switch.
all the yellow relay is doing is energizing the 2 FP relays. the yellow relay is also (?) what gives the 1-2 sec FP run before starting.

to trouble shoot: no particular order.
with key on
1 ground the wire at the pressure switch. FP should run
2 remove the connector on the AFM or push down on the plate to energize the yellow relay. FP should also run.
3 check for power and ground on the connector to the AFM.
4 jumper pins 30 to 87a on the YEL realy:
the FP relays should energize
power on pin 1 of the rev limiter
power on the wire going to the pressure switch. (wire removed from switch).
(if there is no power on this wire, but there is power on pin 1 of the rev limiter, the rev limiter is bad)
5 jump pins 30 to 87 on both FP relays to test FP's

( this is assuming fuses and wiring are good)

you can really start anywhere.

i am not a 930 guy, this is just based on the drawing and what little i have done on tims car, mostly over the phone.
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Last edited by timc; 07-13-2011 at 05:44 PM..
Old 07-13-2011, 05:42 PM
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Quote:
Originally Posted by timc View Post
Good explanation on how this works from my brother, I sent him all of my wiring diagrams so I can just call when I have a problem....this was the speed sensor/O2 sensor relay. Both contacts are in same relay, from this thread:

Fuel Pumps not working with Ign.



the drawing i have shows the speed relay or rev limiter side cuts out at 7k, and the other side is for the O2 sensor. it shows it cutting out at 3k.

tim's relay had several broken solder joints. one was on the coil for the FP's. the others where on some of the major pin joints. some even for the O2 side. so for those that have bad relays' pull them apart and just resolder the points i mentined.
you can apply 12v to pin 7 and ground to pin 5 to test the relay. both relays should pull in.
(i actually used a 9v battery)

my explanation to tim on how it worked:
look at the fuel circuit as 2 seperate circuits. one is the 2 FP relays, the yellow relay(contacts), the rev limiter, and the pressure switch. the other circuit is the yellow relay(coil) and the AFM switch.
the AFM switch removes ground from the yellow relay, de-energizing it when the engine is running.
the FP circuit gets its ground through the contacts of the yellow, then the rev limiter then to the pressure switch.
all the yellow relay is doing is energizing the 2 FP relays. the yellow relay is also (?) what gives the 1-2 sec FP run before starting.

to trouble shoot: no particular order.
with key on
1 ground the wire at the pressure switch. FP should run
2 remove the connector on the AFM or push down on the plate to energize the yellow relay. FP should also run.
3 check for power and ground on the connector to the AFM.
4 jumper pins 30 to 87a on the YEL realy:
the FP relays should energize
power on pin 1 of the rev limiter
power on the wire going to the pressure switch. (wire removed from switch).
(if there is no power on this wire, but there is power on pin 1 of the rev limiter, the rev limiter is bad)
5 jump pins 30 to 87 on both FP relays to test FP's

( this is assuming fuses and wiring are good)

you can really start anywhere.

i am not a 930 guy, this is just based on the drawing and what little i have done on tims car, mostly over the phone.
I have a pretty good handle on all the little bits and pieces that make the pumps run...or not, but for the relay under the seat I would just as soon bypass the entire piece, but to take the time to trace it all out was daunting. Good information, thanks for sharing, this one belongs in my printed archives.
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Old 07-13-2011, 06:11 PM
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[QUOTE][there is the overspeed relay under the drivers seat that ties all this worthless crap together./QUOTE]

Is this also known as a DME relay?
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Old 07-13-2011, 07:14 PM
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[QUOTE=oilonly;6134670]
Quote:
[there is the overspeed relay under the drivers seat that ties all this worthless crap together./QUOTE]

Is this also known as a DME relay?
Nope, aint no DME on CIS cars. That's for electronic fuel injected.
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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 07-13-2011, 07:43 PM
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thanks for the laugh this morning Mark..

It's kinda funny cause I've been there with that thing.

I opened mine up a year or so ago and it also looked like new inside before figuring out the male round electrical pins on it needed a little scraping to remove some of the invisable corrosion or whatever that grew on them over the last 25 years to make it work right again.

I had already installed a hidden backup switch that bypasses the entire over engineered and layered fuel pump relay circut that stretches from the front trunk relays, to relays under the driver seat, and continues with more relays and switches in the engine compartment.

That electrical stuff is unreliable after 20 years and like an upside down oil filled ignition coil mounted on the fan housing waiting to leak and burn out.. will leave you stranded in a bad place some day, it's just a matter of when.
Old 07-14-2011, 06:43 AM
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I am so going to throw all of this Sh#T away when i go to EFI
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Old 07-14-2011, 11:50 AM
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