Fuel Fuel pump won’t prime

Redboy88 · May 30, 2024

So I’m having a hard time on a 88 mustang I have that gives all the wires but one power on the fuel pump relay(pink/black). I’ve checked my grounds on the eec and they’re on tight but I am assuming it’s not completing the circuit by not grounding it it just sends power to everything but not the fuel pump. Idk if there’s a way to just make my own electric fuel system wires. I’ve sent current on the tester under the hood and no fuel pump prime it just makes relay click and I’ve checked my inertia switch it’s by passed and no volts

Mcmahst · May 30, 2024

Can you manually ground the fuel pump to ensure the wiring and relays are all good? It would be helpful to know which side of the wiring is suspect. Lets us know what you find.

AeroCoupe · May 30, 2024

So first thing is you should be applying a ground to the self test port under the hood to get the fuel pump to run. The EEC supplies ground to the fuel pump relay via Pin 22. This wire goes to the self test port and then to the fuel pump relay.

If in fact you did ground it and the relay clicked then that means the coil in the relay energized and should be sending power to the pump. You need to test the pink/black wire for 12V+. If no 12V+ then check the orange/light blue wire for 12V+. This wire gets power from the starter solenoid through a fusible link (see diagram).

If they bypassed the inertia switch there is most likely some wire hacking else where.

Redboy88 · May 30, 2024

When I tested it I did ground it to the tester it just makes the relay click. There’s 2 black and pink wires coming out of my relay one is hot and one isn’t and when I give it power I hear the fuel pump. The orange and blue wire is hot as well as the yellow and green and black and orange. I’m not sure if this is the eec. I did the bypass myself I haven’t messed with the rest of the wiring besides that.

AeroCoupe · May 31, 2024

Tan/Light Green is ground from EEC on Pin 22 or ground supplied at Test Port - you provided ground at test port and relay clicked so coil in relay is functioning which also means the Red/Black wire is getting 12V+
Red/Black is 12V+ from the Inertia Switch - switch is bypassed but this needs to be corrected
Orange/Light Blue is 12V+ from solenoid via fusible link - OP have verified 12V+ so sounds like this is good to go
Pink/Black is power from the relay to the fuel pump - OP states there are two wires of which one has 12V+ and one does not and when OP provides 12V+ to the one without power the fuel pump runs.

Not sure where the Yellow/Green and Black/Orange wires fall into this so can you snap a picture and post it? Again, I am assuming some creative wiring has gone on here.

Redboy88 · May 31, 2024

black and orange wire is from the eec relay,
So the problem could be the pink and black wire not getting 12v? If one wire goes to the fuel pump from the relay where does the other one come from?

Redboy88 · May 31, 2024

So I’ve been digging more and turns out both of the pink and black wires from fuel pump relay don’t get 12v but the rest of the wires do does anyone know where these wires get their volts from?

AeroCoupe · May 31, 2024

Goes the the ECU to confirm fuel pump running I.e. secondary fuel pump circuit.

Redboy88 · May 31, 2024

By any chance do you know how it’s routed that exact wire pink/black ?

AeroCoupe · Jun 1, 2024

So all I can tell you is what is in the wiring diagrams which are here:

1988 Mustang Electrical & Vacuum Troubleshooting Guide (EVTM)

File is too large to upload. Here is link to it on my Google Drive. View: https://drive.google.com/open?id=1on5czXKmpETzxUggWTGtoUuVkJT2UUxN

stangnet.com

Now what my understanding is that two (2) pink/black wires comes off the fuel pump relay where one goes to the fuel pump and the other goes to PIN 19 on the ECU. This is only the case if the car was originally a California mass air car. See image below:

If the car is not a factory mass air California car and you are not the original owner then its possible that someone swapped harnesses in the car. The only way to tell there is to see if there is a FoMoCo tag on the harness somewhere.

Redboy88 · Jun 2, 2024

Ok so I’ve been digging more and more main problem I see is that the pink/black wire to relay doesn’t get power so I checked the computer and it doesn’t have a wire going to it by the diagrams I’ve seen. I’ve jumped my connector under the hood and the fuel pump runs but is constant. I see everything is hooked on right but I can’t seem to find why my fuel pump won’t engage as I turn the ignition on

Noobz347 · Jun 2, 2024

Check for [Ignition On] power coming out of the ignition switch.

Once you've got your hands on it, also check that it remains constant-ish while cranking.

AeroCoupe · Jun 2, 2024

I should have lead with that ECU does not have to “see” power on PIN 19. You just get the code.

It could also be that the ECU needs to be repaired. They are now in the range of 35 years old and the caps and other parts are aging out.

Ford Mustang 5.0 A9L A9P C3W A3M X3Z ECU Repair Service

Ford Mustang 5.0 A9L A9P C3W A3M X3Z ECUEngine Computer Repair ServicePlease fill out the R&R form here once you've placed your order.A Trusted Product with LIFETIME WARRANTY QUICK TURN AROUND TIMEDomestic and International Shipping available! Our Team is Available Monday - Friday 9am to 5pm...

www.theecuexchange.com

Redboy88 · Jun 5, 2024

Last thing I know I’m getting somewhere so
Orange/blue wire is constant hot that’s good,
Red/ black wire going to inertia switch and ignition it’s also good turns on and off,
Pink/black wire is getting ground and once I send volts to it it turns on fuel pump so that wire is good,
Tan/ Lt green wire just gets straight up volts after turning ignition on I assume since it’s a ground it has to stay Ground not get any current and it leads all the way to the computer all the wires have been checked no damage on them but I do find it confusing how it has volts and therefore not turning my fuel pump on with the key. When I ground the wire itself from the tester in the engine bay I do get power to it with the key it’s just constant. I’ve came into 2 conclusions either one the computer is just toast or two I’m just not figuring this out. If it is the computer any place near Illinois or online anyone recommends getting it either fixed or get a new one? Btw I’ve done an engine rebuild but I’ve plugged everything in besides the egr and the o2 sensors since I am just having it a work in progress but the egr will be deleted, I’m wondering as well if those things are off if it’s tripping the computer to not work?

Noobz347 · Jun 5, 2024

Have you tried pulling codes?

Redboy88 · Jun 6, 2024

Noobz347 said:
Have you tried pulling codes?

No I haven’t how do I check?

AeroCoupe · Jun 6, 2024

Jesus man...that should have been the first thing I asked.

Electrical - How To Pull Codes From EEC-IV In 86- 95 5.0 Mustangs

@Noobz347 - The code dump procedure isn't in the sticky - you may want to add it... Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on. Dumping the computer diagnostic codes on 86-95 Mustangs Revised 26-July-2011. Added need to make sure the clutch is...

stangnet.com

But I am going to go out on a limb and say the ECU needs to be sent off for repairs. This is who most of us use:

Ford Mustang 5.0 A9L A9P C3W A3M X3Z ECU Repair Service

Ford Mustang 5.0 A9L A9P C3W A3M X3Z ECUEngine Computer Repair ServicePlease fill out the R&R form here once you've placed your order.A Trusted Product with LIFETIME WARRANTY QUICK TURN AROUND TIMEDomestic and International Shipping available! Our Team is Available Monday - Friday 9am to 5pm...

www.theecuexchange.com

Noobz347 · Jun 6, 2024

AeroCoupe said:
But I am going to go out on a limb and say the ECU needs to be sent off for repairs. This is who most of us use:

Yeah, hopefully the ECU will tell on itself.

BlackHawkfox · Nov 9, 2024

Noobz347 said:
Yeah, hopefully the ECU will tell on itself.

Di

Redboy88 said:
Last thing I know I’m getting somewhere so
Orange/blue wire is constant hot that’s good,
Red/ black wire going to inertia switch and ignition it’s also good turns on and off,
Pink/black wire is getting ground and once I send volts to it it turns on fuel pump so that wire is good,
Tan/ Lt green wire just gets straight up volts after turning ignition on I assume since it’s a ground it has to stay Ground not get any current and it leads all the way to the computer all the wires have been checked no damage on them but I do find it confusing how it has volts and therefore not turning my fuel pump on with the key. When I ground the wire itself from the tester in the engine bay I do get power to it with the key it’s just constant. I’ve came into 2 conclusions either one the computer is just toast or two I’m just not figuring this out. If it is the computer any place near Illinois or online anyone recommends getting it either fixed or get a new one? Btw I’ve done an engine rebuild but I’ve plugged everything in besides the egr and the o2 sensors since I am just having it a work in progress but the egr will be deleted, I’m wondering as well if those things are off if it’s tripping the computer to not work?

did you ever figure out the issue I’m having the exact same issue to a tee. But my ecu should be fine since I swapped them.

Fuel Fuel pump won’t prime

New Member

lube between the nut and the face. I know my lubes

New Member

lube between the nut and the face. I know my lubes

New Member

New Member

lube between the nut and the face. I know my lubes

New Member

lube between the nut and the face. I know my lubes

New Member

Stangnet Facilities Maint Tech... Er... Janitor

lube between the nut and the face. I know my lubes

New Member

Stangnet Facilities Maint Tech... Er... Janitor

New Member

lube between the nut and the face. I know my lubes

Stangnet Facilities Maint Tech... Er... Janitor

New Member

Similar threads

Privacy & Transparency

Privacy & Transparency