Look behind the RH headlight to the right of the radiator. There's four
relays mounted linearly to to a metal support. The one closest to the
engine is the fuel pump relay. The fuel pump fuse is mounted in it's own
dedicated fuse holder closest to the fuel pump relay.
The pump receives current through a parallel circuit. One side is a set of
contacts in the oil pressure switch, the other side is the pump relay. When
the key is placed to run, the pump relay is closed by the ECM for two
seconds to pressurize the fuel rail. The pump is turned on again by the ECM
during crank. Once the ECM senses the engine is running, it deenergizes the
pump relay. But since there is now oil pressure available, the fuel pump
contacts of the oil press. sw. are now closed and the pump continues to run.
I reckon they design it this way to prevent the pump running after a wreck
and adding pushing fuel out of a broken line. I had a problem similar to
yours on my '93 3/4 ton Chevy diesel pickup which has a similar pump
control circuit. The contacts of the oil pressure switch had developed high
resistance and the pump was only getting 7 volts. But since your Buick has
to sit for awhile before it will restart, I'm thinking that the windings in
the fuel pump are opening up after the pump runs awhile and warms up.
After it sits and cools down, the circuit remakes and the pump will run
again until it heats up. My boy's '93 Century has a pump that will only
develop 25 psi when it should be supplying 41-47 psi and will barely run.
I've got to drop the tank and change the pump out tomorrow. I've got an
Alldata subscription for the car and since it's the same as yours, if you
want I'll email you a graphic of the pump electrical schematic. If you
check that schematic and wait till the car dies on you, you could put a
meter on the output wire going from the pump relay to the pump right after
it died. (Pull the relay out of the socket first). If it shows an open
circuit, them I'm likely right about the pump windings opening up. I'd
like to know how you come out on yours.
Look under the hood behind the r.h. headlight. There are four relays in a
row, left to right, attached to a support to the right of the radiator. The
fuel pump relay is the one closest to the engine. The fuel pump fuse is in
it's own dedicated holder closest to the fuel pump relay and also attached
to the support.
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