Cascade Crew

Xophertony

those at cows remember that besides my distributor falling apart, it was taking me FOREVER to start my car. this was caused by a failed fuel pump relay. the car would not start until the oil pressure switch built enough pressure to bypass the relay and start the fuel pump itself. i replaced the relay at cows, and now the car starts instantly.

however, now the fuel pump remains running when the ignition is off. this is intermittent. i believe this to be caused by a failing oil pressure switch. it's been acting funny for a while. not sending oil pressure info to the gage when the car is cold. intermittently not sending any info at all. weird stuff. i bought a new one a while ago.. it's been in the trunk awaiting install. i think tomorow or Saturday will be that day.

just wanted to share/vent.

chevymad · Posted: Fri Jun 20, 2008 6:33 am Post subject:

The oil pressure switch is designed to carry half the load of the fuel pump, the relay is supposed to be carrying the other half. With one not working it might have overloaded the other.

Xophertony · Posted: Fri Jun 20, 2008 9:36 am Post subject:

sounds reasonable.

aaron_sK · Posted: Fri Jun 20, 2008 11:29 am Post subject:

Aren't the oil pressure sender and oil pressure switch sepperate on that car? When I did my Autometer swap I had to replace the oil sender, but the switch was farther down the block.

blue89 · Posted: Fri Jun 20, 2008 1:17 pm Post subject:

it says in the schematic that "SWITCH POWERS FUEL PUMP IF ECM FAILS" That says to me that you don't need it. If the ECM fails to turn the pump on then hard wire the relay to switch power. It does not load share, that would be poor design. So if the relay has failed and it still fails to start you probably have a bad oil pressure sender or its missing.

I've powered my fuel pump from a standard bosch relay for a few years now with no troubles. Just keep a spare relay in the glove box just in case.

iansane · Posted: Fri Jun 20, 2008 2:53 pm Post subject:

Xophertony · Posted: Sat Jun 21, 2008 12:02 am Post subject:

Ian- as long as your relay never goes out you never will.

Aaron_SK- they are separate on a stock 88 engine. switched to a combined (three pin) unit in 89. however, after going through two upper ones in two months, and having the damn thing break requiring me to pull the distributor (or at least the cap) to get it out i decided "screw this" and snagged a three pin 89+ harness out of the junkyard and a napa brand 3 pin sensor. nothing but problems ever since. i have a second napa one i picked up.. but i am debating throwing it away and getting a GM one. think i'll run it and see what happens.

napa electronics are my main car problems.

chevymad · Posted: Sun Jun 22, 2008 4:22 pm Post subject:

Notice in your diagram that both circuits are parallel. This means with both circuits intact and working each is only carrying 1/2 the load while the car is running. Now if one fails full load goes through the other. Which results in either cranking till you have oil pressure to start, or no backup for the relay. The relay is just a generic relay.. probably 30amps.. which is more then enough to run the fuel pump by itself. Who knows what gm used in their switches. And I've had problems with napa sending units leaking as well.. probably gone through a half dozen of em.. finally gave up and let it weep

Xophertony · Posted: Sun Jun 22, 2008 6:40 pm Post subject:

put in the new one today.
while under there i noticed the wire loom (convoluted tubing to some) was melted and drippy. the wires underneath looked okay. so i attained some of that high heat silvery wire protection, and used that for the block temperature sender, o2 sensor, and oil pressure sending unit. should stay cool now.