This is a rewrite to my earlier question. I have a 94 F-150 4x4 5.0. I have a continuous loss of power and horrible fuel mileage and after driving for 10 to 15 miles, the engine comes on for approx. 30 sec then goes off. When light goes off the engine keeps running but looses ALL power. I can't maintain current speed and no acceleration even when I push pedal to the floor. But, if I push hard enough to kick it out of OD, the engine coughs twice, rpms come up and the way I go for about 2 min and then the light comes on and the hole process starts again. Code said bad O2 sensor. Changed sensor. No change. What else could it be?

have your fuel pressure tested. also, could be bad catalytic converter.

Inspect your oil dipstick for fuel smell and your fuel regulator tested during fuel pressure tests. If smells like gas and smokes black, change oil and filter, then get your regulator replaced. There was a recall for those. It can include your vehicle. you can write down your VIN and call your dealer to see.

What code are you getting for the Lambda, "O2 Sensor?"

We need your build date, your service codes that are in memory and hard fault. This is correctly done with a STAR tester, when you have 2 digit codes. after eec-v, an NGS is used. Recalls and TSB's must be eliminated. System prechecks are to be performed. we need your fuel pressure.and fuel volume tests. You can simplify your issue by showing the vehicle to your Ford service dpartment, and awaiting their information check, and basic tests, and road test to verify concern. Ask their leading EEC tech to answer you without this info, and see what you get.

I should mention, the system prechecks include inspections for base engine concerns. a vacuum gauge is used by a technician as well. some issues on a 5.0L can be present without setting codes. there is literature published about it. since the dealer already knows it so well, and we are not getting any data, and it's twenty years old, you need professional help.

In the event your vehicle has multiple fuel tanks, you could have pump, fuel diode, and selector valve concern. contaminated fuel will disrupt any fuel system. Having dirt lying in the fuel rail or settled into the selector valve yet still getting past the filter allows it to get there, it can get stirred up and wreak havoc. Then get passed, then do it again. The resulting HC content in the exhaust can freak the HEGO sensor out. This is why I encourage you to seek dealer help. The pumps, valve, diodes, recalls, and bulletins can be a mess to weed thru when your truck is not hanging there for inspections as part issues come up. also, the initial diagnosis may be verified with professional gauges that a technician uses and drives it at the same time to test a hypothesis. Dont try this at home folks.