Mr. Green Genes

I need some help with a poorly running 1995 F-150. 4.9L I6 w/F.I. About 140,000 miles. Split exhaust at the manifold, Y's back together into tandem catalytic converters. Dual fuel tanks. 7000 mile on spark plugs and wires, distributor. Intermittent check engine light and hesitation and low power above about 1/3 throttle. I also frequently find that the oil breather cap has come off at the valve cover. The codes read.., (I am paraphrasing the wording from notes I jotted down in the O'Reilly Auto-parts parking lot) 111 - Not switching fuel system @ adaptive limit. 173 - O2 or running rich (perhaps the was something about the EGR voltage in this one?). 181 - O2 unable to switch, lean during part throttle. I replaced the oxygen sensor which seemed to help some but the problem persists.

jt351

Well if your truck has a Mass Air it could be dirty, or you have some big vacuum leaks. Also check your fuel pressure, should be 50-60psi and go up when revving.

joshtowal

I may be way off base here, but...with the loss of power, the piston rings could be worn and letting the fuel air mixture blow by the rings and creating extreme pressure in your oil system. Maybe somebody else can speak up about this. In the mean time, you might want to do a compression or leak down test to confirm or deny that.

Edit: try putting a lighter to your oil dipstick. If there is that much blow-by, that thing should light up like the 4th of July.

joshtowal

You do have a vacuum leak. The part about the fuel system being at the adaptive limit; when there is unmetered air entering the system (i.e. vacuum leak), the fuel system will attempt to make up the difference by feeding more fuel up to a pre-specified limit (adaptive limit). With the unmetered air and the incapability of the truck to cram enough fuel through to balance out the mixture, the 02 sensor will simply read "lean". Just check carefully around your intake manifold and any vacuum lines, and you should find the leak in no time.

Mr. Green Genes

Thanks Josh, good advice. My search for a vacuum leak so far has only been the spray around with carb cleaner and listen for the RPM change. The compression/leak down is also good advice. I've never heard of the "lighter on the dip stick" troubleshooting method. Would a lighter at the dipstick hole, while the engine is running, tell me anything?

papa tiger

A lot of blow by and the bic will blow out immediately. Not recommended practice though. An unlit propane torch, slightly on, will cause an increase in Engine RPM at vacuum leak also. More sensitive to small leak, bad clamp, small hole/split in hose. Works best if you have torch with hose for flexibility.