No power under Load, Engine has a lean missfire! Does anyone have suggestions? on 2000 Ford E-250

I have checked fuel pressure and performed a fuel volume test. I disconnected all 3 catalytics and drove, same problem. When I cycle the ignition while running the engine accelerates fine 2 times, then it goes back to having a lean misfire. I sprayed Throttle body cleaner down intake hose while the engine was bogging and it accelerated up in RPM's. I cleaned the Mass Air flow sensor. The only code I have is for the EPC sensor (P1747). I checked for vacuum leaks. The problem is with all the cylinders. Remember it accelerates perfect when ignition is cycled while engine running. Please let me know if you have any suggestions. Thanks Mike

by in Miami, FL on October 29, 2012
3 answers 2 comments
ANSWER by on October 30, 2012
have you ck'd fuel pressure under load. install a f/p gauge and drive down the road and see if you are loosing fp
COMMENT by on October 30, 2012
I have a gauge on it all the time fuel pressure is stable between 32 at idle and 42 under load. The wierd thing is that while running if I quickly cycle the key it accelerates perfect two times then goes right back to no power when accelerates. Like if the computer is resetting runs good, then it compensates and goes back to the lean condition.
ANSWER by on October 30, 2012
sounds like a vacuum leak...the ecu remains in open loop when you cycle the key and once it reaches closed loop, it lets the MAF take over...but the MAF does not pick up the vacuum leak.
COMMENT by on October 30, 2012
It has a plastic intake manifold, I got a long piece of hose and listened throughout the bottom and sides of the manifold, I also sprayed carb cleaner with nozle throught and did not find any leaks. I am thinking that maybe the MAF sensor or ECU is giving me the problem, but I am baffled. I only have a laptop with a generic OBD-11 connection and it doesnt give me to much information. I also dont have the specs for the MAF at Idle or at different RPM's.
ANSWER by on October 31, 2012
Do you have a vacuum guage? Hooked up and read correctly , that can give some useful info , that a scanner won't.

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