Why both fuel pumps stopped working at the same time on 1990 f-150?

Answer 1

check your fuel inertia switch. It is probably located behind the passenger side kick pannel. Once you find it check to see if the red button at top is pushed down if it is then check your fuel pump relay.

Here are some things you can check.

If it is an electrical problem you may need to buy a test light to fix the problem. I am not high on a meter in this kind of a problem as you can get false readings and make you run around in circles.

Lets start with the PCM Power relay (see photo in my link below).

Have someone turn on the key while you have your hand on it.

Did it click (change states/turn on)?

NO then you are not getting power from the Ignition switch, maybe a fuse or bad ground. Let us know and we will help you more on this problem.

YES then ground pin #6 of the DLC (test) connector with the key on.

Did the fuel pump relay click and selected fuel pump come on?

If the fuel pump relay clicked and the selected fuel pump did not come on we could have an open safety (Inertia) switch. Try resetting it by pushing down on the button on top. The switch is located in the passengers kick panel. You also could have an open fuse, bad fuel pump, bad fuel pump relay or an open wire in this circuit.

If the fuel pump relay did not click then you have a bad fuel pump relay or bad wiring in the fuel pump relays coil circuit.

If the fuel pump relay clicked and the selected fuel pump came on then the PCM computer is not grounding the fuel pump relay or you have an open wire from the computer to the fuel pump relay.

The Fuse panel under the hood.

http://i54.Photobucket.com/albums/g91/subford/Electrical/Fuse%20Panel/Hold/EngineCompartmentFusePanelwithke-1.jpg

The DLC (test) connector:

http://i54.photobucket.com/albums/g91/subford/Fuel/Hold%20all/DataLinkConn.jpg

Your fuel system wiring

http://i54.photobucket.com/albums/g91/subford/Fuel/Hold%20all/Fuel-sel1993.gif