Okay. Short and sweet

4.0 OHV
145,000 miles

Engine idles at 550 or so rpms
When you goose it at idle, it hesitates (like the engine just stops for 1/4 a second)

General running and you get low power, poor fuel economy (8 mpg or so)

I know the cat is in rough shape and already have plans to swap it out.

Fuel pressure is 38 psi engine off, and 30 engine on (I think this was it, I can't remember and plan on doing it again tonight)

Anyways

Symptoms

Low Vacuum (14" Hg)
Low Power
Horrible acceleration in 3rd, 4th or 5th gear.
Poor Gas mileage
Slightly rough idle
1/4 second hesitation on the throttle
Oil around the threads on the #5 spark plug (with a fuzzy white head) and another plug (can't remember which one) was oil fouled.


Done So Far

Swapped Fuel Filter
Cleaned MAF
Replaced Spark Plugs
Replaced Spark Plug Wires
Cleaned Throttle Body
Checked operation of MAF
Checked operation of TPS
Retorqued Lower Intake Bolts (using the apparently incorrect outside - in method)
Retorqued Upper Intake Bolts
Checked for blown head gasket (Chemical test came back negative)
Tested Fuel Pressure (38 psi before start up and 30 psi at idle)
Checked compression (140 - 150 psi on the drivers side bank... couldn't get the damned compression tube into any of the cylinders on the passenger's side)
Sprayed Brakleen all over the motor and no change in engine.

Some other stuff I can't remember.



Truck has NO EGR system. I checked, thoroughly.


What I think could be the problem.
-Low fuel pressure could be either dying fuel pressure regulator or a leak between the fuel rail and intake manifold, maybe a bad gasket there.... I have no idea how to check to see which it is.
-Low Vacuum leak could be a leak between Manifold and Motor (but I retorqued those bolts and there was not a single sign of improvement) or it could be caused by excessive backpressure from the exhaust
-Oil fouled plug could be just a worn valve stem seal or could oil be leaking from the intake manifold?

I'm not afraid of spending the cash to buy replacement parts, I just don't want to replace what isn't broken or breaking.



Anyone have any ideas what I can do next? Really need this truck to be working before the even worse weather hits.

 

Check the Purge Valve and / or lines connected to it. Look especially at the one coming in at the bottom of the throttle body. They like to dry rot and probably pinch off completely when the truck is running.

 

Thank you.

Why would that cause the problem tha I am seeing?

 

Every time that line pinches off it will lose power and make your motor cut out. The lines carry fuel vapors. Up in the front of your compartment behind the driver's side headlight is where it's located. There is like a hose with an elbow and those dry rot big time too. It's an odd sized one - end of the hose is smaller diameter than the other??! I just wallowed a fuel line out and slapped it on there. If your getting poor, poor mileage it's almost a dead giveaway for me that it is this.

 

I found that the hose that goes from the Evap Canister to the fuel tank was rust rotted at a connection at the back bottom of the engine bay.....

Does anyone know if this, or if the purge solenoid were not opening would cause any of the issues I am seeing?

The hose between the throttle body and Purge solenoid, and between the solenoid and cannister appear to be in good shape.



and fuel pressure at idle is 39 psi.

 

Any of that stuff can cause problems. I think I changed the purge canister valve on mine and 3 hoses. You can get the entire system from Ford for like $180 not including the canister. I think the canister is like $80 or something can't remember.

 

any info on this.... i am having the same exact problem with the same year and engine

 

have you tried running some kind of fuel system cleaner in it, sounds like your fuel delivery system may be a little gunked. i know if i don't keep on top of mine (fuel filter every 40,000, Injector cleaner every 6 months or so) it tends to get bad mileage, also the quality of gas your using, im not saying fill with premium, but some off the wall gas stations tend to have some bad gas sometimes.

 

i put lucas fuel treatment in it every other fill up