CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

No fuel pressure. 88 F 150

Hi;

New member with a question I hope you can help me with.

Does anyone know where to find the fuel pump safety cutoff switch on this truck?

The one that shuts off fuel in the event of an accident…

My fuel pressure went from good and running to zero. Replaced the boost pump(on frame) and the big filter between it and the fuel rail.

I already looked under the dash near the steering column and in the passenger footwell. Checked the firewall on the engine side too. Where is this switch anyway? Also tried replacing the pump relay to no avail…

Any other common problems with this truck that would cause this to happen?

Thank you very much for your help.

I don’t remember off the top of my head where the inertia switch is located on this type of vehicle but I would be extremely surprised if the inertia is the problem.

Look at the underhood diagnostic connector where the codes are pulled. There should be a tan wire with a green stripe although there are a few exceptions to the rule. Run a jumper wire from that wire connector to ground and turn the key to the RUN position. If you hear the pump run and the truck then starts you will know the inertia and relay circuitry are good.
This is for test purposes only; do not allow the ground wire to remain in place.

This would mean there is likely a problem with the pump relay ground circuit inside the ECM or the ECM is not receiving a PIP signal from the ignition module.
Your truck is a TFI-IV ignition model and these are prone to ign. module problems anyway. Hope some of that helps a bit.

The inertia switch is generally located in the cab, under the dashboard on the right side. The switch is reset by pushing each of 2 buttons on the switch simultaneously (some models use switches with only one reset button).

Your queestion made me curious to know if the owners manual has the location of the fuel cutoff switch.

The owners manual for my 87 Ranger does show the location -complete with pictures- of the “fuel pump shutoff switch.” As cougar mentioned it’s under the dash/passenger side where the carpet meets the firewall.

See your owners manual.

The cutoff switch is the perfect place to test for voltage from the pump relay when you ground the wire from the pump relay as OK4450 mentioned.

For how to ground the lead see this link, but ignore the talk about disconnecting any fuel lines.

Simply ground the wire & see if you have 12 volts at the cutoff switch.

http://www.superhighoutput.com/tech_view.php?id=5

BTW, you will find the EEC4 test connector under the hood, but i have no idea exactly where on an 88 F-150.

Hi;
Thank’s for the help!
The boost pump is running, I can hear it when I turn the ign on to the start position. Will not fire unless I add fuel to the intake; ( like WD 40 or carb cleaner). I also hear a click when I turn on the key that I never heard before…
That’s when I hear the pump run…
Where is the TIV-Ign module located?
I already tried replacing the pump relay. ( Not sure which of the two plugs is the relay, both look the same although one is all white wires.)
I did notice a missing ground wire due to corrosion from the engine to ground, I will replace this ASAP. I will add a good ground from frame to engine and frame to Batt.

Is the ECM the block that’s attached to the dist or is it the main computer box and where is each located?
Could the in tank pump be causing all these symptoms?
Will try checking for flow and pressure at tank pump outlet line.
Was hoping the boost pump was the problem as it is obviously easier to replace.
Also; this the stalling, fail to start seems to happen after the engine is hot.
It is a 302 by the way. Should have mentioned that earlier, sorry…

Both pumps should run for 2 seconds each time you turn the key one click.

When ignition pulses are sensed the PCM turns the pumps back on.

So the frame mount pump IS running, but the in tank pump is NOT.

Have you tried the old standby trick of giving the tank a good dope slap with your hand? This trick has gotten a dead pump running again & gotten me back home 2 times.

Does the pump run when you do this?

I have slapped the tank pretty hard (while waiting for the tow truck).
Will try hitting it harder with a BFH and a block of wood.
Had pretty good luck with a needle gun while freeing up brake parts like calipers and line fittings, a little oil and vibration works wonders along with the patience of a Saint!
I can’t tell if the rear pump is running or not, it’s too quiet, so I am assuming the worst. Time to bite the bullet and drop the tank, as much as I was trying to avoid doing that. A new tank and pump will cost more than the the truck is worth!
Time to cash in my chips, I think!
Thank’s for the help.
I am bailing for today; thunderstorms coming and I can’t afford to fry my computer!
Have a good one.