What would cause my truck not to idle and I have to pump the gas to keep it running.

Asked by Feb 12, 2017 at 08:31 AM about the 1991 Ford F-150 STD Extended Cab SB

Question type: Maintenance & Repair

I have a 1991 f150 straight 6 cyl  It will not idle and dies when I give it gas. I've do a complete tune up on it plugs, wires, cap rotor, module and fuel filter. I've checked idle sensor it seems to be working. Does anyone have any ideals this truckdoes not get drove much about twice a month.  

17 Answers


Probably should check the fuel pressure.


How old is the fuel that is in it?

Ok will check fuel pressure. It has two tanks so two fuel pumps right. The fuel is new.


Fuel pressure should be 45 to 60 lbs. Can the engine sit there and idle?

The engine will not idle have to keep pumping the gas. can I get a good reading by just turning on the key or will I need to try to keep it running.


Yes you can get a good reading without it running, but I wanted you to check the fuel regulator by pulling the vacuum line off and see what the reading is on the fuel pressure gauge. Thats why I was wondering if it can run.

Best Answer Mark helpful

If everything checks out I would suspect the ignition module you purchased may be defective.

I have about 57psi for fuel pressure. I put the old module on but same problem. Could the computer be bad. I don't like changing parts but I am running out of ideas. thank you for all of the input.


A couple more things, check for vacuum leaks, hoses, intake manifold, snug up the bolts, check the timing, and also the Throttle Positioning Sensor on the side of the throttle body. Make sure the throttle body is clean, along with the butterfly inside of it.

The truck will run fine as long as I shoot carburetor cleaner in the intake don't know if that means anything but would assume it a fuel problem the only thing that's not been checked is the injectors is it possible they are bad or stuck. I'm just guessing now


Still have that fuel pressure gauge? Do a fuel bleed down test. And when you have it hooked up start the engine and pull the vacuum line off of the fuel regulator. The fuel pressure should raise up about 5 lbs or more. Then shut it off and let it sit. Take note of the fuel pressure. Watch the gauge, it shouldn't really drop more than 5 lbs.

1 of 1 people found this helpful.

Will do this tonight after work. Thanks

Did the test at a idle 47 psi took vacuum line off of regulator and it went to 52 psi shut off dropped about 3psi in 30 minutes and ended up at 48 in about an hour. The only way to get to idle was spray carb cleaner in the intake. Yesterday I had 57 psi but had to pump the gas to keep it running so I tried that today and the pressure did raise to 57psi I hope this makes sense.


Well, this all sounds good. Fuel is not the problem. Have to look for something else. Is the check engine light on? Also need to check for vacuum leaks. I like to use carburetor cleaner when the engine is running, spraying along the intake manifold gasket and the throttle body base gasket.


How did you do on your vehicle? Come up with anything? I like following threw with helping someone..

1 of 1 people found this helpful.

Just fixed it. It was a bad map sensor. I have never had one go bad and act like it did. Thanks for all the help.


Thanks for the reply, glad you gotter.

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