Help ! ... Is it the ECM ?
Question: I replaced the ECM on my Mustang. The engine cranks but not getting fuel, replaced fuel relay under drivers seat.....
I put direct power to fuel pump and car started...what is wrong?
Answer: Thanks for the question. Since your Mustang starts with direct power, it's probably not the ECM.
Not knowing the specifics of your Mustang, Here's what you should check next.
If your Mustang's engine starts and runs fine when direct power is made to the pump, there are a couple of issues you should check.
1. Verify you have power with the key on, to your fuel pump relay.
You should have voltage in the small wire that supplies the internal relay switch (that switches the bigger power in the solenoid).
And you should have power from battery supply into the main positive side of the solenoid (relay). Repair any problems and re-test your fuel pump. If it starts normally, you're good to go.
2. If not...Test the wire from the relay to the pump. If you can power the pump directly from that wire, you'll know it not getting voltage back somewhere from the relay connection.
3. Test the relay separately.
4. If the relay works by itself, it's going to be an issue with power somewhere between the ignition switch, the ECM and a lockout switch to the relay.
If you have an automatic, the neutral safety switch can be the culprit.
If you have a manual transmission, it could be the clutch switch. Best thing to do is bypass whichever one applies to you and see if the car starts normally.