I have a 1990 mustang 5.0. I can't get my fuel system to work. Just had my ecu rebuilt and still no progress. Fuel pump only comes on if I send 12+ to one wire on relay under driver seat. Ive tried everything i know to do. All fusable links under hood is good. Ive jumped the inertia switch trying that. Please help. Im all out of ideas.
1990 foxbody 5.0 fuel system.
- Thread starter staceyj
- Start date
#4 deals with the fuel pump issues but honestly start at the top and work each step to find the issue.
Who checked your ECU out?
Who checked your ECU out?
Had it rebuilt and tested at ecu exchange#4 deals with the fuel pump issues but honestly start at the top and work each step to find the issue.
Who checked your ECU out?
Which wire did you apply power to? The fuel pump relay works by the ECU closing a ground (wire 97). Wire 366 should always have power from the inertia switch.
Here's the wiring diagram below and what to check
Here's the wiring diagram below and what to check
I dont have any power on wires at my fuel pump relay.Which wire did you apply power to? The fuel pump relay works by the ECU closing a ground (wire 97). Wire 366 should always have power from the inertia switch.
Here's the wiring diagram below and what to check
Slow down and read what Mustang5L5 wrote...which wire at the relay did you apply 12V+ to? My guess is going to be pink/black wire if none of the wires at the relay have 12V+. If this is the case then you need to start with the orange/light blue wire which is powering the latching side of the relay visa fusible link at the starter relay on the driver inner fender. This should have 12V+ at all times regardless of the ignition switch position.
Yes pink and black wire. Last time I checked i had constant 12v+ on orange/light blue wire but I will check again.
Okay, so if you have 12V+ there then what you need to check for is 12V+ on the red/black wire when you cycle the key to the “run” position. If you have 12V+ there then in theory the pump should come on for 2-3 seconds when you cycle the the key to the “run” position to prime the fuel system. Pretty sure you know that but wanted to be clear on how it should function.
The ECU will provide a ground or 12V- on the tan/light green wire during the priming sequence and then again when it detects the engine cranking or running.
If you have 12V+ on the red/black wire and the orange/light blue wire with the key in the “run” position you can test the relay by applying a ground to the tan/light green wire at the ECU test connector (under the hood and will be the same color wire that is at the relay) or by back probing the wire at the relay. I like back probing at the relay because I can hear the relay click and I can check for 12V+ on the pink/black wire.
If the relay doesn’t click then replace the relay. If the relay clicks and you don’t get power to the pink/black wire (pump feed) then replace the relay. If the relay clicks and you get power to the pump start chasing the pink/black wire back to the pump.
My guess is it’s relay related. As you have already put power to the pink/black wire and the pump ran.
The ECU will provide a ground or 12V- on the tan/light green wire during the priming sequence and then again when it detects the engine cranking or running.
If you have 12V+ on the red/black wire and the orange/light blue wire with the key in the “run” position you can test the relay by applying a ground to the tan/light green wire at the ECU test connector (under the hood and will be the same color wire that is at the relay) or by back probing the wire at the relay. I like back probing at the relay because I can hear the relay click and I can check for 12V+ on the pink/black wire.
If the relay doesn’t click then replace the relay. If the relay clicks and you don’t get power to the pink/black wire (pump feed) then replace the relay. If the relay clicks and you get power to the pump start chasing the pink/black wire back to the pump.
My guess is it’s relay related. As you have already put power to the pink/black wire and the pump ran.
key on, you should also have 12v on the red/black wire. If you don’t, check the inertia switch the rear.
The intertia switch is fed by the EEC relay in the pass side kick panel. So if you go to the rear of the car you should have 12V on both sides of the inertia switch to ground with the key on. If you dont, you will need to check the EEC relay. If oyu do, the issue is at the relay under the seat.
The intertia switch is fed by the EEC relay in the pass side kick panel. So if you go to the rear of the car you should have 12V on both sides of the inertia switch to ground with the key on. If you dont, you will need to check the EEC relay. If oyu do, the issue is at the relay under the seat.
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