Hey All

i have a 1990 f250 460 efi. The problems i am having is after the truck warms up it has a bad hesitation when you excelerate. Feather the throttle and it takes off. Problem 2 is when i shut it off it it is hard to restart crank on it and wont start. Hold the throttle open and crank it and the motor will eventally start and chugs black smoke. Very rich. Eventially it will run and clean out. Any help is appreciated!!

 

Fuel pressure comes to mind.Your spec is 30-45 psi at idle and should hold after shutdown. Also, I would check your fuel pressure regulator. If it has a vacuum line on it, pull it off. Replace the regulator only if gas comes out of the vacuum nipple, getting sucked into the vacuum line and richening the air/fuel mix..

 

On a pressure gauge it is idling at 25 to 30.

 

What did you find when you removed the vacuum line from the pressure regulator?

 

i removed the vaccum line had vaccum and know fuel leak. Changed anyway just to rule it out.

 

That regulator leaking was likely your problem, it will greatly richen the mixture by sucking the gas into the intake via the vacuum line. I would recheck your fuel pressure and pull the line off the regulator, the pressure should go up, stay stable and not drop much as you goose the throttle if the pump is in good shape.

 

Just in case the problem is still present,
A malfunctioning or disconnected coolant temp sensor can keep the fuel mixture richer than required.
That might explain why it is fine when cold which is when additional fuel is required, but once warmed up that additional fuel is no longer required and now we have a rich fuel condition..Might be a good idea to check that out .

 

The sensor that runs the temp gauge or is there a differnt one?

 

Coolant temp sensors usually have 2 wires going to them, whereas temp senders only have one wire (Usually).
Coolant sensors are usually mounted near the thermostat housing or close by.

 

intake air temp sender was the problem!!! Its fixed! Thank you