Cant Find Fuel Pump Relay/fuse

[ALLBoostAWD]

I currently have no power to my fuel pump and cannot find where the fuse or relay is for it? I have searched online and still cant find anything. Please help.

1990 TSI AWD

 

[kenamond]

I currently have no power to my fuel pump and cannot find where the fuse or relay is for it? I have searched online and still cant find anything. Please help.

1990 TSI AWD

Fuse box under the driver's side dash.

 

[ALLBoostAWD]

which one? I dont have a diagram of the layout, and there are a few empty slots. I also did not see it listed there when I looked for it online. And all the fuse's there are good?

Is there a relay for the fuel pump?

 

[DSMopar]

I'm bumping this because I spent the last 30 minutes looking through the FSM and found nothing on this... is there even a factory fuel pump relay or is it part of the ECU?

 

[steve]

It's really pretty simple, it takes longer to describe than to read it from the diagrams. You'll find it in the MPI diagrams either in the electrical manual under circuit diagrams or in the Fuel section of the main FSM.

I'm going to talk 1G specific but the 2G uses a like setup and I'm also talking about stock functions. If you have a fuel pump rewire done thing can be different. You can also look at http://www.dsmtuners.com/forums/problem-diagnosis/263224-mfi-mpi-relay.html#post151211808

The fuel pump is driven by the half of the MPI relay mounted on the passenger side of the center console support below the radio and to the rear of the car from the ECU. It's a gold box bolted to the support.

The fuel pump side of the relay has two coils that can activate the contacts. Power is from the ignition switch IG1 terminal to pin 3 on the relay, the large black w/white stripe wire. Output of the relay is pin 2 on the large black w/green stripe which runs to the check connector in the engine bay and to the fuel pump. The wire changes color to black w/white stripe somewhere around C-59.

The inputs (coils of the relay) are from the starter circuit on pin 9 (large black w/yellow stripe) and the ECU on pin 7 (white w/red stripe). The starter input is activated by 12v from the starter relay (which is activated by the ignition switch and safety interlocks) running through the coil to the ground at pin 6 of the MPI relay. The ECU input is active low. The hight side of the coil is internally connected to the power from pin 3, the ECU completes the circuit by pulling it's pin to ground when it sees the engine spinning (CAS pulses).

Normal operation is that driver engaging the starter, that activates the relay and powers the fuel pump while cranking the engine. Once the engine starts spinning the ECU sees CAS pulses and it grounds it's input and will continue to do so for a few seconds after it stops seeing CAS pulses. So, the starter primes the fuel system and once the engine starts the ECU keeps the pump running after the driver releases the ignition switch. If the engine doesn't start the fuel pump will run for a few seconds and turn off or it will turn off as soon as the key is turned off.

Some people report that their pump primes when they first turn the key on. This is most often heard from 90 1G's and it's suspected that their CAS glitches on power up triggering the ECU to turn on the pump. There is nothing in the accessable 90 ECU code that would otherwise turn the fuel pump on and nothing in the hardware. 2Gs have different relays over the years that don't have both inputs for the fuel pump so the ECU may prime the pump.

Diagnosing problems requires you to check both the connectors back by the pump and at the MPI relay.
Starting at the relay helps.

You should see battery voltage at pin 3 when the ignition switch is in the RUN or START positions.
You should see battery voltage at pin 9 when the ignition switch is in the start position and the Park/Neutral or Clutch Safety switches are open.
You should see battery voltage at pin 2 whenever the fuel pump should be running.
You can force the relay to activate by grounding pin 7 wit the ignition on.
You can force the pump to activate by applying battery voltage to the check connector in the engine bay.

Back at the pump the large black wire is the ground and the large black w/white stripe wire is the power.

Most rewires use the black w/white stripe to activate a relay that switch a direct battery feed to where the black w/white stripe wire used to connect to the pump.

 

[DSMopar]

Ah so the MPI relay isn't just a simple 4 pole? Has a circuit for ECU and fuel pump?