I have this 1991 F150 4 x 4 , Some may remember me a couple of weeks ago talking about it being a new toy. With the lift kit and big tires. My wife thinks I need to grow up.... I told her it was my mid life crisis....
So to get to the point. I have a slight problem with the motor when I'm driving down the highway. It will be running along perfectly, and then all of a sudden it cough's, a couple of times. back fire's out the throttle body, and then carries on.... It may do this one or two times, then run normal again for awhile. At first I thought is was water in the front fuel tank, (truck was sitting for 2 years.) Then when I switched tanks. It seamed to go away, so I was convinced that was the problem.... Nope. Now it does it on either tank. I changed the plugs, Cap, rotor. ( was surprized it even ran with the amount of rust on cap and rotor) Fuel filter, cleaned the throttle body, added gasline antifreeze and some injector cleaner to both gas tanks.
Still sputters and spits on occasion. One time the truck actually seamed to die, and then just as I stepped on the clutch, and was about to restart it. It came back to life without turning the started over. ????? The tach actually dropped to zero, for a split second. Anybody got any ideas on what I could check into next? I changed the Ignition moudule. on the side of the Distributer, but that was replaced with another used one.

 

Have you checked the timing?

backfires throught the carb/throttle body can be a timing issue.

 

Yes it's set at about 12 degrees advanced. It doesn't alway back fire, It's more like a really bad cough. What really confuses me with it.... Last night and this morning... it didn't cough once. ..... maybe it was the fuel filter???? yet you would think it would fix the problem right away.

 

Im at a loss then.

Might check with in the engine forum or the forum for your year of truck.

 

you could also have a valve sticking...