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Randall C
Randall C, ASE Certified Technician
Category: Subaru
Satisfied Customers: 11131
Experience:  ASE Master Certified Tech, 32 Years, Foreign.Domestic, Diagnostic Specialist
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1997 Subaru Legacy 2.2 wagon Fuel pump relay is not pulling

Resolved Question:

1997 Subaru Legacy 2.2 wagon: Fuel pump relay is not pulling in. No OBD2 codes are present. 12V + is present at relay coil. It is not grounding out. I have the ECM exposed as my Haynes manual says the MPFI module grounds it. I am ASSUMING the MPFI and ECM are same. I do not have a decent enough wiring diagram to determine where the relay coil ground terminates. I rang out all terminals on the ECM plug and none show 0 ohms.
Submitted: 4 years ago.
Category: Subaru
Expert:  Randall C replied 4 years ago.

Hello, the ECM and the MPFI are 2 different items. The ECm is the computer for the car, the MPFI is the main relay which powers up most computer items as well as ECM. the MPFi relay is located on the drivers but way up behind the dash. If the check engine lights comes on in the car, this usually? means the relay is good. You then need to be looking at cranks sensor as possible problem

 

PURPOSE/OPERATION

FUEL PUMP CONTROL RELAY
The Engine Control Module (ECM) receives a signal emitted from the Crankshaft Position Sensor and turns the Fuel Pump Relay "ON" or "OFF" to control Fuel Pump operation. To improve safety, the Fuel Pump will stop if the Engine stalls with the Ignition Switch "ON".

POWER SUPPLY CONTROL RELAY
When the Engine Control Module (ECM) receives an "ON" signal emitted from the Ignition Switch, current flows through the Main Relay. This turns the Ignition Relay "ON" so that power is supplied to the Fuel Injectors, Mass Air Flow Sensor, Idle Air Control Valve, etc..

 

 

 

MAIN RELAY AND FUEL PUMP RELAY

REMOVAL AND INSTALLATION

  1. Disconnect battery ground cable.

  1. Remove instrument panel.

  1. Remove screw which installs bracket of Main Relay (1) and Fuel Pump Relay (2).
  2. Disconnect connectors from Main Relay and Fuel Pump Relay.
(1)Main Relay
(2)Fuel Pump Relay
  1. Installation is in the reverse order of removal.

 

Customer: replied 4 years ago.

In my 1997 the fuel pump relay is under the main relay. It has 12v on one side of it's coil but will not ground out. In the Haynes manual it shows the control module (with about 50 wires going to it) as the MPFI module. I suspect that is actually the ECM. If so, I can't get continuity on any of its wires to the relay coil. Also, if the crank sensor is defective wouldn't it show up on the OBD2 readout?

Expert:  Randall C replied 4 years ago.

I thought you were referencing the MPFI to the main relay. Sorry. Yes, if you have power on the 2 wires at the fuel pump relay and not the Brown ( which goes to pump) the Violet? wire is the wire in which is grounded by the ECM or MPFI as you reference. the ECm receives signals from mainly the crank sensor for activating fuel pump. The ECM could be bad as well. A bad cranks sensor or any sensor that has gone bad does not always show up as a code or other. You need to read scanner looking for "cranking" signal or RPM etc

 

You need to be sure you have power on 2 wires at the fuel pump relay with key on.If not, wire or fuse is the problem

Randall C, ASE Certified Technician
Category: Subaru
Satisfied Customers: 11131
Experience: ASE Master Certified Tech, 32 Years, Foreign.Domestic, Diagnostic Specialist
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