My wife's car: 93 Ford Escort Escort LX 1900cc SOHC Problem1: Check Engine Light will go on and off while driving. It is never on at startup. It only comes on when car is driven, but may still be on or not when car is stopped and engine is still running. Problem2: In warm or hot weather, when engine is thoroughly warmed up, at highway speeds, usually after 1/2 hour or more of highway driving, at 55mph or above, going uphill and sometimes on a level road.the engine will lose power and buck and will recover if I back off of the throttle. I am unable to duplicate this problem until a warm day in spring. This can happen if the check engine light is on or off. The fuel pressure remains within specs at all times. The fuel and air filters have been replaced. I have also replaced the Oxygen Sensor, and the engine temperature sensor and the spark plugs. I recently purchased a digital OBD1 code reader. KOEO code is 111; Continuous memory codes = 171, 181, and 186; KOER code is 111; Cyllinder test = 90. What is the next step?

Fuel pump fuse went out twice this week on a family member. She was towed two times. First time, they changed the fuel pump fuse, suggested she quit driving so near empty all the time, and sent her on with a $120 bill, including the tow. then it stranded her an hour later. An affilliate station towed her again and now says the relay in the intank fuel pump has failed. they said either she got some bad gas that caused it's demise, or someone put something in her tank. They said when the emptied it, they would be able to tell which. She uses the cheapest gas and the lowest octane, and her valves knock. I thought I had read somewhere that using a lower octane gas CAN cause a fuel pump to fail, but I can't find proof anywhere and can't say this is true. I CAN find places that say the gas source CAN be important more than the octane. (I stick to a Shell station and never have problems) She also feels that since the stations are owned by the same person, and since she paid so much the first time and was sent on her way, that what she paid there should go toward this 2nd bill. I mean, should she have to pay double labor, double diagnostics, etc? It sounds like the 2nd bill will be around $500. Thoughts anyone?