Ok my '86 F150 started acting up the other day. At anything above 1/3 throttle it loses power, bucks, and will backfire through the intake. Floor it in Neutral and it stumbles and pukes fire out the throttle body. I've pulled codes and I get a EVP sensor too low (I believe that the EGR solenoid is the fault there) and a MAP voltage low code. I've tested the MAP sensor and it tests within spec so I wonder if it's not a result of the backfire causing a MAP error - the code will go away for a while if I reset the ECU. I get good vacuum (18-19.5" at idle - throttle snap goes up to 20-21"), idle is rock steady, engine temp and oil pressure are normal.

Could it still be my MAP sensor even if it passes the test? I was thinking fuel pump but it acts the same on both tanks, and since it pukes fire out the intake I'd say it's getting enough fuel. Timing is good (10 deg spout disc. and advances with spout in), plugs, wires, cap, rotor are all brand new and all wires are firing consistantly so I don't think it's an ignition problem.

Any insight would be appreciated!

 

Fire !! wow sounds like a real retarded timing issue to me or advanced. At any rate did you remove your distributer lately? maybe the dtrib gear is warn...

 

Tooooo late - bad fuel filter at the selector valve - didn't even know there was one there!