Electrical Fox will crank but won’t prime HELPP
- Thread starter Tortoler0
- Start date
Mcmahst
5 Year Member
I’m wondering if you have a bad ground. Just for grins, I would remove the relay ground and clean it. Couldn’t hurt.
The relays themselves don’t “ground”. The only ground the relay needs is for the coil side of it which the ECU provides. If the relay clicks then the coil is working. With the Pink / Black wire to having 12v that means the Dark Green / Yellow wire should have 12v as well being it’s getting power from the Pink/Black wire. So if it’s not then the contact in the relay is messed up or you have a wiring problem at the relay like a corroded connector or the new relay doesn’t pin out the same as the original one.
I would think it would be zero as the ECU commands the fuel pump to prime for 2-3 seconds when you move the key to the "run" position. When you move it to the "crank" the ECU commands the fuel pump to run. When the motor starts and you release the ignition cylinder back to the "run" position the ECU will continue to command the pump to run as it "sees" the engine running via the TFI module on the distributor. At least this is my understanding.
With all of that I am still questioning why there is voltage on the dark green / yellow wire after the pump primes. Its like you are getting voltage bleeding across somewhere in one of the connectors.
With all of that I am still questioning why there is voltage on the dark green / yellow wire after the pump primes. Its like you are getting voltage bleeding across somewhere in one of the connectors.
You have had a lot thrown at you. The dark green / yellow wire is not a ground nor should it ever be. The light blue / orange is the only wire that is grounded and that is done through the ECU.
I do not think the dark green / yellow wire should ever be anything but 12v. Again, I think you have a wiring problem and you need to vet that.
I do not think the dark green / yellow wire should ever be anything but 12v. Again, I think you have a wiring problem and you need to vet that.
Looking at the picture. The grey connector at the bottom of the opening is one of the two you need to look at. Comparing it to the wiring diagram I included shows its a 12 pin connector. The other connector is grey as well if I recall correctly. You will want to disconnect them (one at a time) and using a small precision screw driver, squeeze the sides of the female pins so that the gap in the pin closes (touches). Do this to all 12 pins in both connectors and see if it helps.Fuel pump relay wires should get the following with the ignition off:
Red - 0 v
Dark Green / Yellow - 0 v
Light Blue / Orange - 0 v
Pink / Black - 12 v (constant 12 v from fusible link at the starting solenoid mounted on the driver side fender apron)
Should get the following with the ignition on:
Red - 12 v (comes from the PCM power relay)
Dark Green / Yellow - 12 v (comes from the fuel pump relay via the Pink / Black wire when the coil is energized. this goes to the inertia switch and also goes to PIN 19 on the ECU for fuel pump run conformation)
Light Blue / Orange - 0 v (this is a ground generated by the ECU from PIN 22)
Pink / Black - 12 v (constant 12 v from fusible link at the starting solenoid mounted on the driver side fender apron)
Have you checked the Light Blue / Orange wire with the rebuild ECU to see if you are getting ground? Once you have everything confirmed at the fuel pump relay then you need to chase the Dark Green / Yellow wire from under the driver seat to the driver kick panel, and to the inertia switch in the trunk and make sure 12V is getting to that point. If you have 12V to the inertia switch then check the Brown / Pink wire from the inertia switch to the plug under the car at the back of the fuel tank to see if you have 12V there. Back probe the connector on the tank side (Pink / Black wire) and make sure the 12v is carried across this connector. If you have 12V there then you will need to drop the tank and see if you have 12v at the tank connector and then on to to the pump.
Another issue can be the fuel pump ground wire connection in the trunk of the car.
Here is a picture I found on here (thanks @91AOD5.0LX) of the wiring behind the driver kick panel on a '91. You can see a dark green / yellow wire in the connector in the foreground and bottom right. You can pull this connector apart, set the DVM to continuity (https://www.fluke.com/en-us/learn/blog/digital-multimeters/how-to-test-for-continuity), and check to see if this is indeed the wire from the fuel pump relay. If so put the connector back together and back prove for 12v.
This is all I have man so hopefully it helps.
I had to do this 3 years ago to these two connectors as I was chasing an intermittent fuel pump as well. I switched 3 relays in for the fuel pump, I jumpered the two large pins in the relay socket (will give full power all the time) and still had intermittent issues. Since adjusting the female pins, no issues. I actually just did this repair on the connector in the driver door for my power windows (8 pin connector this time). So far it has worked like a charm.
I went ahead and squeezed the female side connectors on both grey driver side connection and also on passenger side green connection I see there is same color wire same voltage so I’m assuming it’s the fp relay to eec connection but also still nothing . What’s left do I have to strip interior and follow the green wire? And also the blue wire had a cut or something there’s a butt connector between the blue wire but there’s voltage there once on the ON position
I don’t think I can explain how the relay works any better than in my previous posts. This is a simple diagram that shows the relay being triggered by ground. This is the same way the fuel pump relay works. The relay coil ground (85) in this case is the light blue / orange wire from the ECU.
Turns out getting 6-7 volts is normal ONLY when you crank the motor or start it do you get 12v to the pump after the initial prime. PCM apparently has to see an RPM signal to ground the relay circuit. After replacing the fuel pump everything works fine. If the shop manual would have said you only get 12v for a couple of seconds to prime then it drops off unless you are cranking or started the motor, I would have saved a lot of time.
Similar threads
