87turbo930

lately my 930 has this problem starting and Ive found it is because my fuel pumps wont turn on.

When i push down on the fuel plate, my pumps dont turn on, every once in a while they will but most of the time they wont. Also when i unplug the electrical connector behind the fuel head the pumps dont turn on sometimes the will as well. Its my understanding that when the connector is unplugged the pumps are supposed to run. Am I correct here???

If im right what would be my next step to check? I dont have a wiring diagram so where do those wires from the fuel head go? Any help or a wiring diagram would really help.

thanks

jhunt@huntinter

For ****s and giggles try these easy-to-do and cheap three things first.

1) replace your fuel pump fuse (even if it looks good)
2) swap your fuel pump relay with another one and see if things change
3) pull the little brown wire off the thermo-time switch (on the cam cover behind the IC piping) and ground it (or maybe not ground it I don't remember)

See if any of these solve your problems before really digging into things.
John

sand_man

There are also two relays (red in color) that are located on the trunk fuse panel...I believe they are the first two relays closest to the driver. They should be listed on the panel cover diagram. You might want to check these.

87turbo930

Ive already tried changing fuses, but ill double check em. Ill check the relays and try the trick on the thermo time switch. thanks.
anyone else have any ideas?
thanks

WERK-I

The only other thing that comes to mind is an intermittent ignition switch.....it has happened to others before.

Dave
'85 Factory Slantnose 930

Last930

Pelican Parts has an article on problems with the fuse box coroding, causing poor/intermitant contacts in the fuse holder itself for the fuel-pump circuit. I had the same problem on my '79 930 and traced it back to a bad fuseholder. Check out the article at Pelican Parts, they feel it is eventually going to happen to many cars due to the design of the electrical circuit, which places a high load on 1 circuit. This causes heat to build up in the small prongs which hold the fuse itself; over enough time the expansion/contraction leads to a bad contact where the prong is riveted to the fusebox. Thus, intermittant contacts and sporadic fuel pump operation. There is a schematic on how to rectify the situation by wiring in a different circuit for each fuel pump. It worked for me!

PorschePhD

If you unplug the sensor wire and the pumps don't come on. Replace the yellow relay in the rear. It is problematic like the DME relay. It will fail and not send a signal to the front relays. They will start to go out and this is what they do. It is not cheap, but should cure the problem. It is very common.

87turbo930

When i unplug the yellow relay and plug it in, I can hear it click on and off. Does that mean it is ok? Or can it still click on and not work correctly? I know it is more than just a standard relay, and I have resoldered the contacts on it before. Should I just buy the relay anyways?

WERK-I

"When i unplug the yellow relay and plug it in, I can hear it click on and off. Does that mean it is ok?"

No, but an ohm meter across the Normally Open, Normally Closed and Common when you perform the plug, unplug relay test would definitely help. The clicking only tells you the relay winding is functioning, not whether the contacts are providing continuity.

Dave
'85 Factory Slantnose 930

PorschePhD

Thanks David, you beat me to it!

WERK-I

I guess my reflexes are still pretty good....for an ol' man!

Merry Christmas, Stephen.

Dave
'85 Factory Slantnose 930

PorschePhD

Many returns!! Merry Christmas!

Cajun

Stephen,

I am having a similar problem with my car, except the problems come when the car reaches operating temp. For some reason, it just dies...almost like someone reached over and turned the key off. It also will die while under boost. Could the yellow relay in the back of the car cause these kinds of symptoms as well??? I spoke with my mechanic, and he said if this "fuse" has a similar function as a DME realay, than it is possible that the yellow fuse is the culprit.

Thanks...