robshil6

88 GTA 5.7 TPI. I have the dealer book but cant find the oil pressure switch and how it works. It is connected to the fuel pump relay! The thing i need to know is the relay comes on with the key for 3 sec then im guessing the oil pressure switch takes over to give the fuel pump and the maf relay 12 volts. so it seems the fuelpump relay is only used for that 3 sec when ignition is turned on! After 3 sec prime i disconnected fuel pump relay and started car and it fired right up so i think im right ?????

Apeiron

The fuel pump relay is energized for 3 seconds after ignition-on to prime, and for 3 seconds after the last reference pulse is received from the distributor, ie. as long as the car is running.

The oil pressure switch is in parallel with the fuel pump relay to continue powering the pump in case the relay fails. The car will run just fine without it even installed.

89fbirdformula

Right, and wrong..

it also kills power to the fuel pump in case of oil pressure drop..a functioning sensor needs to be there, or the connector needs to be jumpered.

DeanJ

It does not kill power to the fuel pump. It is only a backup if the fuel pump relay fails.

89fbirdformula

Go unplug that sensor while the cars running, see what happens...

report back to me.

My v6 89 firebird had the issue, and my 89 formula has had the issue...

Apeiron

What issue?

89fbirdformula

when the switch failed, it wouldnt allow the car to start, it would fire up and die, fire up and die..

jumpered the connector to test, car stayed running..

Also on my iroc, it kept my fuel pump running constantly, changing it stopped that nonsense..

Apeiron

Sometimes they short when they fail and the pump runs continuously.

If it wasn't starting without the switch, then you had other problems along with a bad switch.

89fbirdformula

it would start..and then die, start and then die, jumpering the switch connector allwoed the car to fire and carry on running, replaced the switch, car runs fine..no issues since, and that was back in april i think...

i also had a issue with a maf that failed while the car was cold, but read fine once it got to temp..this was just recently..N20 backfire caused that.

Apeiron

Yes, because shorting the dead switch let it fulfill its purpose as a backup system. In a properly working car, the switch isn't needed.

89fbirdformula

My pump relay works fine, jumpering that triggers it...

however, i have noticed one relay by the firewall thats melted all to hell on the end where the wires come out...but since ive owned the car, none are ever hot or even warm.

Apeiron

Jumping the switch can't turn on the pump relay. The switch isn't in the coil circuit, it powers the pump directly. With the switch shorted, the pump will run with the fuel pump relay removed.

vetteoz

iTrader: (13)

On the TPI cars at least ; the ECM has to see the pump come online from the OP switch (fuel pump signal at ECM in diagram ) along with the dist ref signal while cranking before it will pulse the injectors
See
http://www.corvettebuyers.com/c4vettes/l98.htm

So the switch performs two functions;
as a parallel backup for the fuel pump and a indicator that the pump is running ( or oil pressure is over 4 psi ) which ever way you want to look at it.
However the ECM only references this input while cranking so if OP drops while engine running it will not shut the engine off

robshil6

It reads the signal off the op switch but after the relay goes on for that 3 sec then the relay does nothing op switch takes over when car is running! disconnect the op switch car wont run!

Pillsbry10

iTrader: (1)

on my 92 my header burned the wiring for the op switch...shut the car right off

Apeiron

Your fuel pump relay was bad, or you blew the fuse.