10 MPG & no codes 1999 4.0 ohv

[clamb]

I am getting poor fuel economy, 10 to 12 mpg on highway trips. I have about 230000 kilometers on the truck but only about 20000 kilometers on this engine (the third). Recently had it in to a local garage, where they reset the fuel trim codes, with no gains to fuel economy. Checked the fuel pressure, fluids, scanned for codes, as I was not showing any on my reader, garage found none either. The only thing my reader displays in EV. Will not pass Evaporative systems test on scanner. The only thing that I am aware of that is an issue is the drivers side valve cover gasket is leaking oil. Was wondering if I could be getting a vacuum leak from this. This engine was recently rebuilt, & tranny rebuilt at the same time. Pulled all spark plugs and they look fine, except for the rear drivers plug is a little darker than the rest. All new plugs, spark plug wires, O-2 sensors. I don't know what else to look into. The original engine seized after driving it out of the Ford shop when they replaced the lower intake manifold gaskets when it started leaking coolant externally. (they never changed oil after changing gaskets). I replaced that engine with a new drop in and after about 80000 kilometers this engine blew a head gasket, filling one piston with coolant and hydrolocking. I fear that the 3rd engine may blow too and am afraid to drive the Exploder anymore or any distances with my family.

Is it possible for a sensor to be defective, but not throw codes on the scanner. What tells the engine to "choke" for cold starting /operation, could the sensors think that it is always cold & not trigger fault codes?

Anyone have any suggestions?

 

[rhauf]

does it run at normal temperature? any black exhaust under acceleration? does it start normally? does it misfire? do the cats get extra hot? normal horsepower?

you sure do go through engines.. i've got 230k miles (about 380k) on mine and it runs great. i even take it on long trips. cant say i blame you though after that luck.

 

[clamb]

It seems to start & run well, but doesn't seem to have the power that it should have when climbing hills. Temperature gauge sits in the mid normal range close to the r on the gauge if I remember right. After installing the last engine I had a vacuum leak from around the egr tube where it slides into the plastic housing. I built it up with a couple of coats of O-2 Safe silicone & plugged the leak, but maybe there is still a small leak there??? enough to not let it pass evap test on code reader but not enough to trigger codes? I am thinking about removing that side to reinstall a new valve cover gasket that is leaking. What would I be looking for if I don't pass evap test on code reader?

 

[rhauf]

Im not an expert on codes... but i think all the evap codes are for is fuel tank stuff. leaky fuel cap, charcoal canister problem, etc. vac leaks would probably not throw codes. except perhaps a mixture code (probably lean) but unless it was a big leak, i can't see that it would effect anything more than just the idle.