My 89 truck with a 22r will afterfire if I suddenly let off the throttle if Im going above 50mph. If I drive it for longer than 30-45 minutes it goes way and the idle smooths out. I just put a tune up on it and changed the pvc valve and fuel filter. What has me confused is why it goes away after its been ran for so long. I gets up to operating temp in about fifteen minutes but doesnt run better for right away. Any thoughts???

 

just a side note. Im not sure why but when I relieve the pressure on the fuel tank it seems to run better right away. Also there are no engine codes to help diagnose the problem

 

If the motor is a r and not a re it will not show a check engine light, because it doesn't have a ecm. it might have a restricked vent line causeing it to build pressure ,which could cause a flooding problem.

 

Well. Figured out it was the auxiliary accelerator pump. Just plugged it off till I get a new one to replace it. Runs great. Hope this will help out with the mpg. Thanks for the help