Hi, I have a 1990 ford f150 with a 302. I shut it off and the fuel pump came back on. I turned the ignition on and off and it shut off, but came back on all by its self. Acted the same on both tanks. Any ideas? Ignition switch?

 

You can check the relays and connectors,if they are good ecm is getting ready to head south.

 

The ecm (EEC Computer) can NOT turn on the fuel pump with the key off.
The power for the coil of the fuel pump relay comes from the EEC Power relay and the EEC Power Relay is operated by the Ignition switch.

You either have a bad Fuel Pump Relay or bad wiring under the relay socket.
OR someone has rewired your truck wrong.
Even with a bad Ignition switch the fuel pump relay should only run for on second and quit.
Of course if the power from the Ignition switch is going off and on continuously then the pumps may come on each time the power goes on.

 

Thanks for the info. I am out of town working, so will look at it when I get home. The truck hasn't been rewired. This problem just started. I have another question for somebody, what should the oil temp be at freeway speeds? Mine is at 240 with 20psi of oil pressure.

 

Well, this exact same thing happened on my newly-acquired F350 with the 460 just a couple of weeks ago. I turned the ignition off, the engine quit, but the FRONT fuel pump was still running (tank empty) and the fuel selector switch in the dash was switched to the rear tank. I flipped the switch back and forth with no change, the front pump still kept running

We had the hood open and my friend started moving the relays around over the driver's side inner fenderwell and it stopped. All the wiring is stock as far as I can see.

I have looked at the factory wiring diagram for the fuel tank selector valve and pumps, and can see zero ways how this could possibly be (when you switch the tanks, it disconnects the electrical path from one tank pump and connects it to the other). Even if the fuel pump relay were to stick closed, flipping the selector switch should have interrupted the current path to one pump and connected it to the other.

I plan on investigating this further, as it could definitely cause serious problems (dead battery, fried fuel pump).

Edit: After talking to a friend, I'm convinced that the ONLY way this could happen is a short between +12V and the wire that goes directly to the front tank fuel pump from the switch- that would explain why it continued to run even though I was switching the dash selector switch. My friend moved the wires underneath the hood so that's where I will carefully start looking, once I locate the front tank fuel pump wire.

 

this has happened to me when my fuel pump relay has failed (one of the several times it has). finally i replaced it with a 12v relay i had layin around the shop, weatherproofed it, and have had good luck since. was gettin sick of runnin to get another relay or jumpin out the relay when it went bad on the trails.

 

Update: It's the fuel pump relay sticking.

It's happened a few more times since I posted above, and apparently the first time it happened to me, I could not tell the difference in the sound of the front and the rear fuel pump (so I erroneously though that the front pump was on continuously even though I was moving the selector switch between the two tanks).

In the mean time, if I hear either fuel pump still running as I exit the cab after the engine is off, I pop the hood and smack the relay bracket on the driver's side inner fenderwell.

Someday soon (if not already), we'll have cars so advanced that only using a smartphone to hit them will do any good!