postcar

where is the fuel pump relay located? also the fuse panel the book shows it as fR has to voltage when the key is on, should this be hot then? can't get car to start has new pump installed thanks

Hooked on Vettes

Here's a block diagram of the fuel pump circuit.

The fuel pump relay has 5 terminals.

Pin A is an Orange wire that is 12 volts from a fusible link
and is hot all the time. (Fusible links are tied together at a
stud below the battery).

Pin C is a Red wire and goes to Pin G of the Diagnostic connector
located above the drivers right knee.

Pin D is a Dark Green wire or Dark Green/White and goes to the ECM.
The ECM will apply 12 volts to this wire when it sees reference pulses from
the distributor (engine running or cranking) or when you turn
the ignition key to on it will apply 12 volts for a couple of seconds
to prime the fuel pump.

Pin E is also a Red wire and is the output of the relay and goes
to the fuel pump fuse.

Pin F is a Black/White wire and is ground.

The fuel pump fuse which feeds the fuel pump motor can
get 12 volts three ways.

If you take a jumper wire and apply 12 volts to Pin G of the
diagnostic connector above the drivers right knee the fuel
pump should run. Using this method, 12 volts goes to Pin
C of the relay thru the normally closed contacts and out on
Pin E of the relay to the fuel pump fuse.

Second method for the fuel pump to operate.
When you crank the engine and the oil pressure reaches
around 4 psi, the Oil Pressure Switch will close. 12 volts
from the fusible link will travel thru the Oil Pressure Switch
and 12 volts will be applied the fuel pump fuse.

Third way.
When the ignition is turned to On, the ECM will apply 12 volts
to the fuel pump relay primary coil on Pin D which will energize
the Fuel Pump relay. The relay contacts will close. 12 volts
from Pin A will go thru the relay and out on Pin E. 12 volts
then goes to the fuel pump fuse.

If the ECM sees no reference pulses the fuel pump relay
will only be energized for a couple of seconds.

If the ECM sees reference pulses such as when the engine is
running or being cranked, it will keep the Fuel Pump relay
energized.

The Fuel Pump relay is located on the passenger side of
the Power Brake Booster on the firewall.

The Fuel pump fuse is located in the fuse panel bottom right
labeled FR and is a 10 amp fuse.

Cliff Harris

The fuel pump relay is next to the windshield wiper motor. If you have a 4+3 manual trans the overdrive relay is also on the same mounting bracket.

The ECM turns on the fuel pump (through the relay) for 2 seconds when you turn on the ignition to pressurize the fuel rails for starting. The reason for turning it off after 2 seconds is so that is won't run continuously if you turn on the ignition but don't start the car.

The ECM turns on the fuel pump when it sees reference pulses from the distributor. The fuel pump will run as long as the engine is rotating.

You can force the fuel pump to run by connecting 12 volts to pin G of the ALDL connector. The cigarette lighter is a good source -- it's fused and close by. The fuel pump relay must be OFF for this to work (as shown in the diagram).

[ EDIT ] You can also turn on the fuel pump by unplugging the oil pressure switch and jumpering the orange and red wires together in the connector. [ /EDIT ]

motion vega

did you use the old in tank harness? might be faulty

merrillgtrs

I don't know if you can respond to an old post, but this one relates closely to issues I am having with an 86. let me know if this works.
thanks, merrillgtrs

Cliff Harris

The relays in earlier cars have different pinouts. This diagram is for an '86:

merrillgtrs

cliff, thanks for the reply. what is happening with my 86 is that the fuel pump does not come on and cycle for the 2 second interval when I turn on the key. I have checked the wiring on the fuel pump relay and it all checks out fine for power/function and have replaced the fuel pump relay, I have checked the fuel pump for power from the G plug in the diagnostic port and the fuel pump works fine with 12 volts to it. I have gone through the VATS and done everything including buying a new chip from PCM of NC, I have gone through the fuel rail, injectors and fuel lines and all of that checks out fine with a fuel pressure testor. the big issue is that I only get pressure when the car turns over, and none when the key is turned on without cranking. I get about 45 # of pressure almost immediately on the fuel pressure gauge when cranking but again, none with only the key on. when cranking, at least as far as I understand the oil pressure/fuel pump sensor behind the distributor allows fuel to go to the fuel rail when oil pressure builds up with the engine cranking. beyond that I cannot come up with why I can't get the fuel pump itself to come on with the key in the start position. any help would be greatly appreciated.
pat dedmore/merrillgtrs

playsdixie

you wouldn't be the first guy on the forum to replace a bad relay with another....If you have a gm manual, there's a pretty good troubleshooting tree regarding the fuel pump....

Cliff Harris

Unplug the fuel pump relay. While the engine is running, probe pin C of the fuel pump relay connector, referenced to ground. You should see 12 volts there. If not then there is a problem in the wiring/connectors between the relay and the ECM.

The ECM could be bad, but that is unlikely. They are pretty robust.