1994 4.0 OHV Problems
Okay. Short and sweet
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)
Low Vacuum (14" Hg)
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
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.