1996 ranger with 2.3l engine hesitates and backfires after driving 10-15 miles with no trouble code except p0141 heated oxygen sensor heater failure sensor 2. Changed plugs and wires. Problem presents 2 to 3 times a week not everyday. Fuel pressure tests at around 40 psi engine under load with problem present. Ran engine with mass air flow sensor unplugged no change. Engine also idles a little rough while problem is present.