ok so my 1990 f250 460 truck runs like crap, wont idle, ive got to keep pumping the gas pedal to keep it running.

Could this be a sympton of a clogged cat?

Im gonna unbolt from the down pipe this afternoon, just thought i might get some ideas first.

Later

 

Might be the Throttle sensor. I assume that you have a 351w?

 

its a 460.

 

I'd check the simple stuff before thinking its a cat. Fuel filter, fuel pump. Idle set screw, Throttle sensor.

 

Unless the cat is completely stopped up, I don't think that sounds like a cat. Blocked cat will run fair at low rpm, low power but just won't make power. The honeycomb in the cat on my '90 F350 with efi 460 broke loose and got turned 90 deg. It ran ok below 45 mph but just would not develop any power. What kind of vacuum does it pull?

 

replaced the throttle sensor.

so another sympton is that when you try to accelerate it boggs down and dies.
new plugs, wires, rotor, cap, throttle sensor, temp sensor, fuel pressure reg, timing chain, water pump, ICM, IAC. All new.

Fuel PSI at idle is 30, When trying to keep running its still around 30-35, when i take the vacume line off the fuel psi reg the psi jumps up to 40psi. so thats all ok.

Is there a way to check the ecm out of truck to tell if somthing is bad, or should i check it while its in the truck?

with the idle screw would that affect the acceleration when just stepping on the gas pedal. if i pump it really fast i can keep it running.

 

Well it was the MAP sensor. thank god it was that simple.
Swaped my MAP from my mustang 5.0 and it ran great. Thaks for all the helpfull tips

 

For what its worth.... I check back pressure with an adapter made from an old spark plug. Screws in where the O2 sensor goes. If a pressure gauge reads over 5lbs the exhaust is plugged. I've seen the cat come apart and plug the muffler.