Info. (90 Ford F150 2WD Extended 4.9 I6 EFI, Standard 5 Speed)
I'm getting alot of bucking on takeoff especially in first gear, when I shift to 2nd still bucks but not as bad but will still throw you around. If I get on the hwy. it will be going along fairly well (still has a miss) and then the check engine light will flicker and the bucking begins, only way to stop it is to downshift and ride it out

1. Pulled codes
A. 552 Air management 1 circuit failure
B. 553 Air management 2 circuit failure
C. 565 Canister purge circuit failure
D. 556 Fuel pump primary circuit failure

I've replaced
A. Cap, button, wires, plugs
B. plugged EGR valve, no help
C. Checked EGR valve, was to specs. per Chilton
D. built restrictor plate for EGR no help
E. Replaced Ignition module
F. Replaced Coolant Temp. sensor
G. Replaced Idle air valve
H. Replaced PCV valve and hose

I have twin tanks runs the same on both. it would almost not run, the only way I can get it to run halfway right is to plug EGR vac. line, it still bucks but is drivable. Any help would be greatly appeciated

Thanks

 

i have an 84 carburated I6 and i had a very similar problem. i found out that the timing was the problem... after much searching the timing says it should be set at 10 or 14 but mine runs best @ 16 BTDC.... hope this helps

 

could also be hot spots on your flywheel , or bad spring in the pressure plate there isnt a way to check without removeing the trans and clutch. the way to fix it is to surface the flywheel , if it can be done and replace the complete clutch kit. good luck ,bob

 

My cousin had this exact problem with here car. Manual tranny, FI, would periodically buck when hard accelerating. It turned out to be a fuel delivery problem, a relay somewhere was going bad.

 

after you replaced all those parts and reset the check engine light did you recheck for codes , im thinking that the egr not only has a bad vacum side but its stuck open. you could have a combination of things happening . tie rod ends , ball joints , tires out of balance, have a friend drive slightly behind you and try to duplicate to symptems.with them watching the front tires of your truck, something else ive seen is a bad frame ground, if you computer isnt grounded it can cause all kinds of problems, good luck, bob