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mark houghton mark houghton is offline
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Join Date: Jul 2008
Location: Central Washington State
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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.
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, 06:11 PM
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