Question about 1991 Ford F150

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Backfire through the intake

I have a 1991 f-150 that smeels of raw fuel ,runs very rogh and the fuel pump will not cycle off.This problem happened insantaniously.If there is any ideas it would be helpful

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This problem sounds like a fuel pump relay that is stuck and will not magneticly release rule out relay cheapest fix

Posted on Sep 11, 2008


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if you spray intake cleaner into the intake with the air snorkel off and it starts then i would say you have a fuel pump problem.the backfiring was probably caused by the motor all of a sudden going will have to check the fuel pressure with a gage it should be about 35lbs pressure to run the car.if the pump needs replacing change the fuel filter.

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My 93 towncar runs rough cold. it backfires up through intake i replaced plugs, wires and one coil pack, coolant sensor. i read codes 226 and 542. it runs ok warm, but can still hear misfiring, it feels...


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Starts quickly cold. must crank 5-8 seconds when warmed up. I let fuel pump run before cranking. Get faint gas smell but no visable leak. New plugs wires cap and rotor. 165k

At that mileage, it's possible that you have one or more injectors that are beginning to leak. When that happens you need to crank the engine over longer in order to clear the raw fuel from the intake and re-pressurize the system as well. Also check the ballast resistor (white ceramic block with two wires going to it) on the drivers fender back near the firewall. I can't remember exactly what it does but do remember that it alters the way the pump operates after warm up.

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My 1999 isuzu rodeo ran out of gas and now it won't start even with 4 gallons of gas. It cranks, the lights don't dim, but it does not even sputter or anything.

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This can clog or plug the strainer so much that it prevents fuel from being pulled up into the fuel pump.

The fuel pump can be damaged by the debris that is pulled up, causing it to fail.

I suggest a pressure test. You can spray a small amount of wd40 or carb cleaner into the intake while being careful, if the vehicle tries to run, then more than likely it is your fuel pump.

Be careful for backfires, you are spraying a flamable product into the intake and any timing problems could cause sparking to create a backfire. Just stand to one side and be careful.

good luck

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Is it a vortec engine if it is your fuel injector may be the problem. Chevy ran one injector on the vortech engine it is under the upper intake manifold, it has 6 plastic hoses running to each cylinder under the manifold. if one of these hoses are leaking its dumping raw fuel into the manifold during hot soak. that fuel is getting picked up by intake air when trying to start. and flooding it out hence hard to start. gasoline evaporates rather quick so what fuel was in the manifold when you park for the night has evaporated by the next morning so no raw fuel for intake air to pick up easy start. Seen this problem many times. pretty easy fix but a bit pricey around $200

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