Question on fuel pump / bad ecu

5.0Torx · Mar 30, 2010

Hey guys,

So ive been reading so many search threads and looking at jrichkers/tmoss/stang+2birds diagrams and help pages that my eyes are glazed over lol.

I am among the group of unlucky saps who have had their fuel pump stay on constantly, and those help pages arent as specific for this issue as they are for the guys whose fuel pumps wont turn on at all. I finally read that if you unplug the ecu (i actually had mine out of the car so i could test the pins #46 vs 40 and 60) and turn the key to the on position, if the fuel pump doesnt turn on at all then you know the ecu is bad.

I just did that on my '93 and thats what happened.

Is that correct? I need a new ecu?

TIA!!!

liljoe07 · Mar 30, 2010

Another option is to check the condition of the 3 blue electrolytic capacitors inside the ECM. Look fors signs of leakage onto the board. These can cause the same issues you are having.

sjhm9102 · Mar 30, 2010

i had that same problem just open the ecu up and smell for or look for like what joe said

5.0Torx · Mar 31, 2010

yeah i opened mine up. Didnt see or smell any leakage. Everything looked pretty good, honestly. But i dont know what else it could be.

LocoSway · Mar 31, 2010

The ECU provides power to the fuel pump relay, so if you unplug the ECU your pump will not turn on.

Have you already checked the fuel pump relay?

What codes are you getting with KOEO?

5.0Torx · Mar 31, 2010

I have replaced the fuel pump relay and the new one did the same thing as the old one. Just runs forever and ever.

I tried pulling the codes, but i dont think the ecu will give them to me until it stops priming the fuel rail, which in my case is forever. So i cant pull them.

LocoSway · Mar 31, 2010

On your car the ECU should send a signal to a red wire to the inertia switch. From the inertia switch the signal goes along a red and black wire to the relay. This should energize the relay and let it close to let the power flow to the fuel pump. It would seem that there's a constant voltage to the relay that's keeping the circuit closed. I'd put a meter at the inertia switch on the red wire with the ignition off and see if there's current. If there is then I'd say the ECU is bad. If not, then you'll want to continue trouble shooting.

Let me know if that red wire is always hot.

liljoe07 · Mar 31, 2010

LocoSway said:
On your car the ECU should send a signal to a red wire to the inertia switch. From the inertia switch the signal goes along a red and black wire to the relay. This should energize the relay and let it close to let the power flow to the fuel pump. It would seem that there's a constant voltage to the relay that's keeping the circuit closed. I'd put a meter at the inertia switch on the red wire with the ignition off and see if there's current. If there is then I'd say the ECU is bad. If not, then you'll want to continue trouble shooting.

Let me know if that red wire is always hot.

ECM doestn send a signal to the inertia switch in his car. Or the earlier Fox cars. The ECU only sends a ground to the relay. On earlier Fox's the Inertia Switch just shut off power to the relay. Later cars it just shut of the pump, and relay stayed energized.

liljoe07 · Mar 31, 2010

5.0Torx said:
I have replaced the fuel pump relay and the new one did the same thing as the old one. Just runs forever and ever.

I tried pulling the codes, but i dont think the ecu will give them to me until it stops priming the fuel rail, which in my case is forever. So i cant pull them.

View attachment 224217

Just ground the STI to the body.

Use a test light and clip the clip on the postive side of the battery. Stick the probe of the test light into the STO. Turn key on, but dont crank it.

See if codes flash.

Question on fuel pump / bad ecu

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