BIGTYME

I have a 1989 f150 4x4 4.9l 5spd 142000k that just has me stumped . I have been a mechanic for nearly 22 years and have NEVER encountered a problem like I have . It has a intermediate miss in it , but when it is missing I can leave it running and lightly tap on the fuel pressure regulator and it will stop just briefly . I have replace the regulator 3 times 2 with factory ford OEM and one from Napa . ( NOTE I WILL BUY A DAMN THING FROM AUTO ZONE, ADVANCE AUTO, OR ORIELLY'S ) With that being said as long as I drive it light throttle it does ok but if I have to get on it a little bit it starts as SOON AS I LET OFF THE GAS . I have changed fuel filters both on the rail and the one in the tank on the first fuel pump , as mine has 2 fuel pumps . I have never in my life seen a vehicle miss when u let off the gas almost immediately . Need any advice on this .

BIGTYME

And it has no PCM codes

BIGTYME

Could it be a blocked return line ? But it doesn't do it always . I can drive it 5 minutes or 5 days before it does it

infantry351

Possibly a stuck check valve for the deul tanks???

BIGTYME

No it has single tank .

infantry351

Then why 2 pumps??

BIGTYME

It has the tank pump and the boost pump on the frame rail

infantry351

Is that a factory pump? I don't think my 96 has that.

BIGTYME

yes it is factory

sdmartin65

How new or old is the ICM. Im sure your aware a bad can cause similiar to your symptoms.