Fuel Pump Power problems.......90 MK VII

Joes Mark

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:( For some reason I am having intermitent power problems with my fuel pump. There has been several occasions that when I turn the key on, I do not hear the fuel pump kick in and the car will not start. The pump has been replaced and I'm still having the problem. Two time this past week the car would not start at the train station after work. Both times after leaving it over night the next morning I go to start it and it fires right up. Any Ideas as to what might be the problem?
 
I had a similar problem... Some sort of fuel delivery problem when starting. It happened rarely, and then more often.

After a couple months, it got bad and the warm engine might cough a couple times and die at a stop sign.. (low rpm).. and not restart.

Spraying some Starting Fluid into the intake would fire it up, so I carried a can with me.
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studied the manuals.. checked fuel pressure.. Fuel pump seemed ok, since it worked just fine when it ran. Injectors were ok..

I got stuck in traffic in the rain.. the last straw.. and finally took it to the shop. They found and fixed the problem in about 5 minutes... i recall spending less than $100.

My problem was the fuel pump relay. I never bothered to find out where it is, but I think it's mounted on the firewall among the several other relays..

I've had a couple bad relays on this car. (88 Mk7) The brake pump relay and another one (firewall near the master cylinder) went bad. The contacts were burned.
 
"They changed the fuel pump relay. Only time will tell if it was my problem."

Did the shop discover the relay to be bad all on their own, or did you suggest it?

I was looking at the wiring diagrams and the pump-relay/EEC relay connection has it's own test lead. I think a bad relay will spit out a code on a Code Reader, and there's little doubt the shop hooked one up.
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My problem with low-rpm shut down might be explained in the manual, but it's kinda difficult to interpret. Here's some stuff the manual says:

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Technically, there are 2 fuel pump relays. One is inside the EEC (electronic engine control), and one is external. They work together, depending on operating conditions.

When the ignition is in the OFF position, both relays are open (no power).

Turn the ignition ON, and the EEC relay closes. This powers/closes the external fuel-pump relay and starts a timer. The fuel pump runs (since the pump relay contacts are closed).

If you don't turn the key to START within one second, the timer disconnects power, the relays open, and the fuel pump is de-energized, and it shuts down.

That one second is long enough to pre-pressurize the fuel system, but the pump cannot continuously pump fuel with the key "ON" and the engine off.
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Turn the key to START, and the EEC module operates the pump-relay to provide fuel while cranking.

After the engine starts and the key falls back to the ON position, power to the fuel pump is again supplied by the fuel-pump relay (that relay stays closed and power to the pump is continuous).

After that, the EEC senses engine speed, and shuts off the fuel pump by opening (grounding) the fuel-pump relay if RPM falls below 120 RPM, or if you turn the key off (and kill the engine).

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So it looks like starting and low-RPM fuel pump operation are not as simple as it might seem, since the EEC computer controls and monitors a few things.

Ain't nothing worse that wondering if the car will start.. I know I was worried about it for a long time.. even after that relay was replaced... but I never had another starting problem.. knock on wood.

Good luck with yours.
 
For what it's worth,the external relay is supposedly in the trunk,driver's side,mounted to the lower hinge.That would put it somewhere near the reset.
 

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