My 1988 F150 will buck and jerk only after warmup.
Have done a complete tuneup and changed fuel filter. Even cleaned EGR valve.
Truck is EFI equiped.
Did find a Ford service bulletin stating something about a TFI Module.
What is a TFI Module?
Any help appreciated! Had it at 2 mechanics and they could not help me!
Thanks Herb

 

is this at idle, or at cruising speeds? Could be several things depending on which it is. Definitly clean your throttle body and air bypass valve first, if you haven't already. could also be a fuel pump going out. do you have single or dual tanks?

 

My 89 did something like this and it was due to a bad module in the distributor. I don' know if it is called a TFI or not tho.
DannyP

 

TFI stands for Thick Film Ignition. The dist. module is named that prolly because of the design of the board within the module and it's relation to the computer(PCM). The module is what is mounted to the outside of the distributor. Newer models have it mounted to a heat sink on the firewall. as for your problem, it could be either the ignition or fuel pressure as the other guys stated. One guy from another post stated he had trouble with a corroded connector at the PCM Relay which is also a good thing the check,and,that includes all relays as well as other connections like the module connector,sensor connectors,and fuel pump connectors.
Phillip

 

Thanks for your reply.
I do have dual tanks, but only use the front one cause the guage in the back one don't work.
The truck idles beautyfull, but at any speed below 2000 RPM it bucks and jerks. Only after warmup and now that the weather is getting warmer, it is also getting worse and I do notice it at cruising speed 55-65 MPH, but not as bad!
Had the fuel filter replaced and the throttle body cleaned to no effect.
Herb

 

Since there is only one gauge for both tanks, either the sensor in the tank is bad or you have a simple break in the wiring. Try to fix it. I would use the back tank even if the gauge dosen't work, else the fuel in it will go bad or, since you probably have in nearer empty, it could collect condensation and possibly rust or when you do use it give you watery fuel. If you havent used it in a long while you may want to inspect the inside condition, possibly add some dry gas. Without the gauge you can always multiply the capacity with your worst gas mileage and subtract a safety factor, then fill it and drive say 150 or 200 miles before refilling. Ultimately, though, I would get the gauge fixed.

 

Did resolve the bucking and jerking and strangely enough, the problem was not tune-up or fuel related. It appears that the plug on the alternator was bad and arcing.
The alternator went bad and I replaced same and was advised by the parts store person to change the plug due to the connectors in the alternator having signs of arcing.
I replaced both the alternator and the plug and lo and behold the truck runs like a charm.
I would have never guessed that the fault was at the plug.
Herb

 

Did resolve the bucking and jerking and strangely enough, the problem was not tune-up or fuel related. It appears that the plug on the alternator was bad and arcing.
The alternator went bad and I replaced same and was advised by the parts store person to change the plug due to the connectors in the alternator having signs of arcing.
I replaced both the alternator and the plug and lo and behold the truck runs like a charm.
I would have never guessed that the fault was at the plug.
Herb

 

If that was the problem, the reason is the computer gets it's " Voltage Correction" feed from the alternator harness. The voltage correction is a signal used by the computer for idle speed changes(low charge rate = an increase in idle speed to compensate) as well as other things that are too lengthy to discuss here.
Phillip

 

 

Hello I am new to site and a first time owner of my very own truck its a ford f150 1990
and I seem to be having the same problem as others when I drove it home today about 25 miles there was a point that i didnt think i'd make it at about 35-55 it started jerking BAD I felt as if the whole truck was gong to fall apart.. I am a woman and if i take this to a shop there going to say i need a new transmission and Im hoping it has nothing to do with that any advise would be very helpful... thank you Laura