930 fuel pump problem

[makoco]

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.

[equality72521]

The ground to both fuel pump relays (J17 and J49) goes through the boost relay and the boost limit switch. But, you need to have air flowing past the air meter plate to close the circuit to the air meter contact. Push down on the air meter and see if both pumps run without jumping the ground. If it's still only the front pump you have to bypass then you have an open ground to that relay.

[makoco]

Thanks for the information and the diagram, I will check the boost control relay, I did read through bosh bulletins that the pump relay is grounded through the control unit where in deed the boost pressure limited is wired to.

Also the engine has to spin at least 30 rpm in order to close the ground circuit through the control unit (in order to avoid having the pump running when the ignition is on a the engine not operating (like in case of an accident))

My concern is the fact that I did turn on the ignition switch and after noticing that the pump did not operate at once I proceed to jump the relay, primed the pump and w/the relay jumped proceed to start the engine and it did.

After that I check the relay and found out it was operating normally proceed to check the contacts on the relay circuit to found out that the ground loop out of the relay was not completed. Furthermore I did ground the relay and the circuit was complete closing as well the pump circuit and obviously operating.

When I grounded the relay it was also connected to the brown wire coming from the control unit. It is my concern that I have probably damaged the control unit.

Is it possible to damage the control unit when connecting the ground (the way I did)