Fuel Having issues getting my fuel pump to work.

evintho · Nov 30, 2022

When turning the key to 'ON' the fuel pump should run for a couple of seconds, then shut off....correct?
That doesn't happen. The only way to make it work is to jump power to pin #87 (Bosch style relay) and it'll run constantly. Doesn't build up fuel pressure 'cause there's no fuel in the tank. Just trying to get everything working before I fire it up for the first time.

Some context:
'93 5.0/AOD and wiring harness swapped into my '54 Customline. New Walbro pump installed in the '54 tank. Running factory fuel injection with ECU and all the factory wiring. No inertia switch. I'm using the large factory wiring diagrams for reference.
Wiring is:
#787 PK/BK from pin 30 to starter solenoid on inner fender.
#238 GRN/YEL from pin 87 to ECU and also to fuel pump.
#361 RD from pin 85 to ECU.
#926 BLU/ORG from pin 86 to ECU and also to data link connector.

With key 'ON', there's no power to #787 which makes sense 'cause the start solenoid contacts haven't closed to transfer power from one side to the other. However, when the key is ON shouldn't the ECU provide power to the relay to cycle the fuel pump? I can hear the ECU relay click on.
I've been fooling with this for days and have kinda hit a wall!

evintho · Dec 1, 2022

Dumb question. Is this what's meant by 'jumpering EEC test connector to ground'? Just running a wire from the lower right terminal to a ground stud?

General karthief · Dec 1, 2022

Well, not exactly.

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

There is a wire that gets connected when doing the code check, look for it in the harness near the test connector.

evintho · Dec 1, 2022

Thanks for responding General! Actually, I'm not dumping codes, I'm trying to troubleshoot why my fuel pump isn't priming. I'm following JRichker's 'fuel pump troubleshooting for '91-'93 Mustangs'.

Relay: Turn on the key and jumper the ECC test connector as previously described. Look for 12 volts at the dark green\yellow wire (relay controlled power for the fuel pump). No voltage there means that the relay has failed, or there is a broken wire in the relay control circuit.

So, my pic isn't correct?

General karthief · Dec 1, 2022

Ahh, I think that will not work, is the harness in a mustang?

General karthief · Dec 1, 2022

Cranks OK, but No Start Checklist for Fuel Injected Mustangs

Cranks OK, but No Start Checklist for Fuel Injected 5.0 Mustangs model years 1986-1995 A word about this checklist before you start: it is arranged in a specific order to put the most likely failure items first. That will save you time, energy and money. Start at the top of the list and work...

www.stangnet.com

This will give you wiring diagrams and tell you how to jump the fuel pump.

evintho · Dec 1, 2022

OK, is this how to jump the fuel pump? Red wire from upper right terminal to Pin 46 terminal?
The harness isn't in a Mustang but I've swapped a '93 motor/trans/ECU and wiring harness into my '54.

General karthief · Dec 1, 2022

Yes, a jumper wire or paper clip from the tan/green wire to the black/white wire fuel pump should run.

General karthief · Dec 1, 2022

On a side note, you should wire in the inertia switch in case of collision, in case of fire, the pump will feel the fire fuel and your will burn to the ground in minutes.

evintho · Dec 1, 2022

Yeah, I just jumped it and no joy.
I can run power directly to #87 on the relay and the pump works.
I have a Bosch style 5 pin relay and with the key ON I've got 12v to every terminal except #87. There's even 12v to #86 which is the lt blu/org wire that runs to the ECU/data connector. That's on the other side of the relay coil...shouldn't that be 0 volts? Maybe not.
I've swapped relays also with same results.
I think all that's left would be a broken lt blu/org wire that runs from the ECU to the relay. I'll have to check that.

evintho · Dec 1, 2022

OK....I cut the lt blu/org wire 6" out of the ECU and ran a jumper wire from there directly to #86 on the relay and the fuel pump primes! The wire must be broken somewhere inside the harness. Now I have to replace it but at least I found the problem! Thanks General!

General karthief · Dec 1, 2022

Your welcome but you did all the work, I just regurgitated info from others here that are more experienced than me.

manicmechanic007 · Dec 1, 2022

Like to see a pic of your 54
I will compare my diagrams to yours if you need
It's the processor that grounds that fuel pump relay for a few seconds
You need to be looking at the ground signal into the green FP relay from the processor imo

evintho · Dec 1, 2022

manicmechanic007 said:
Like to see a pic of your 54
I will compare my diagrams to yours if you need
It's the processor that grounds that fuel pump relay for a few seconds
You need to be looking at the ground signal into the green FP relay from the processor imo

Check my build thread which is in my signature. Looks like I've got it figured out though, thanks!

Fuel Having issues getting my fuel pump to work.

evintho

evintho

General karthief

wonder how much it would cost to ship you a pair

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

evintho

General karthief

wonder how much it would cost to ship you a pair

General karthief

wonder how much it would cost to ship you a pair

Cranks OK, but No Start Checklist for Fuel Injected Mustangs

evintho

General karthief

wonder how much it would cost to ship you a pair

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wonder how much it would cost to ship you a pair

evintho

evintho

General karthief

wonder how much it would cost to ship you a pair

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