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makoco makoco is offline
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Join Date: Nov 2008
Posts: 2
930 fuel pump problem

I have an 86 930 with the following problem.
I stored the car for several years in an enclosed warehouse, the car was working in great condition.

After a few years I now have the time to enjoy the car, when I find out the fuel pumps were not working properly, so I replaced the rear pump, replaced most of the fuel in the tank and added a bottle of fuel treatment to the new fuel, the car was working erratic as it seem to be running out of fuel when the turbo produced positive pressure. The front pump was making a lot of noise, so i figured it was due to be replaced

I replaced the front fuel pump. Prior to installing the cover, I open the switch to make sure it was working properly. To my surprise the pump did not operate. I checked the relay and was operating normally, I did bypass the relay (right at it's mounting base) and the pump worked so I started the engine.

I proceeded to check the relay and the contactor was not closing unless I ground the brown wire. The blue wire (+) was energized as you open the switch. To my understanding the problem seems to be with the grounding of the relay circuit as if I run a ground to the contactor it closes the contactor and the pump operates.

I look at the wiring harness to see weather there is a loose connection and everything seems fine. I notice both pumps run in the same circuit and are protected by the same fuse same goes to the wires that control the relay.

My question is the following:
Is the brown wire (negative side of relay contactor) simply go to a common ground directly or is it grounded through a control device (part of the fuel management system),as I suspect it is; where should I check for continuity or what component should I look after to assure proper functioning? The car is original and has 30k miles, so I don't want to disassemble all the factory harness to follow given wire as all wiring seems to be original.
Old 11-29-2008, 01:53 AM
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