I have a 1990 F150 with a 4.9 5 Speed Manual 4x4. Everytime I crank it up when the engine is cold it revs to about 1500 RPMS like normal but then it dies. I have to hold my foot on the gas and give it juice for it to stay alive. The worst part about it is I will be driving and the engine will be warm and when I push in the clutch and put it in neutral to come to a stop the RPMs drop so fast that alot of the time the engine stalls. Or when I am at a stop and I am turning the wheel, normally the engine might bog down alittle bit to power the power steering but lately it will just stall. On top of that the engine seems like it is choking at low RPMs and is lacking power. From a dead stop I will start to accelerate and it seems when it hit 1600-1800 RPMs it takes off. But anything under those RPMs and it is bogged down. I checked the air filter and it is clean, I have not done anything to it recently to make it do this. Any Ideas???

 

Vacuum leaks, dirty or plugged injectors. These can cause all this. Injectors you can clean by running injetor cleaners through the gas on fill ups. or have them professionally cleaned. Vacuum leaking hoses you have to search for.
My 85 would run greta in cold starts, but run crap once warm, but the enghine needed a rebuild. That may not be your case. Have you done a compression test.

 

no I havent done a compression test. the engine runs much better when it is warmed up but it still has a lack of power. I am thinking that I have a leak around my intake manifolds or a vacuum leak. I want to run a compression test and see what my compression looks like.

 

I have an 84 F150 I6 1 bbl w/ auto trans. This weekend I replaced the plugs, wires, dist cap & rotor, set the engine timing off of top dead center on #1, changed oil/filter, battery, H2O pump/gasket, themostat, H2O outlet/gasket, upper & lower rad hoses, plugged some vac tube fiitings that weren't hooked up to anything. Also adjusted carb as best as possible off of adjuster screw on bottom. After all of this, the engine will idle alright after revving it several times to prevent it from dying, idles fine after 3 or 4 revs, and it will die whenever I'm stopped at a stoplight, so I have to keep one foot on brake pedal and other on gas pedal to keep the engine at slightly higher rpm or it quits.

What is wrong, can't find anymore vac leaks, timing is correct (in theory, may have to retime off of #4), distributor has been set. It has been suggested that I may need to rebuild the carb, but not sure. The wires for the ign module had obviously caught fire sometime previous to my purchase of the truck, I removed and rewired that section of the harness. Does anyone have a clue to what's up with my sick puppy?

Also, does anyone know if it's poosible to drop a 4.9L I6 w/EFI from a 1996 F150 into a 84 F150 w/carb? And if possible, what has to be done to convert EFI I6 to carbeurated I6? (in case current engine is toast).

 

Had the same problem down in Mexico, thought it was the gasoline. Turns out the carb was coming apart. Tightened all the screws and it was fine.

 

Try torqing you intake manifold

 

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