Questions and Answers

A Rich F-150 Q. My husband has a 1989 Ford F-150 4x4 truck with a 302 engine with 97,000 miles on it. It has fuel injection. The problem: The engine light was on so he took it to a joint vocational school and they put it on the analyzer - they found nothing wrong but when he took it home it was out of time so much that he had to re-time it. It started using a lot of gas - where he was getting 250 miles per tank he now gets 120-130 miles. It loads up on gas and blows black smoke out of the tail pipes. He has changed the 02 sensor, MAP sensor, throttle position sensor and the heat sensor. He took the battery terminal off and re-calibrated it. He stills has the same problem. Can you help with any suggestions. Thank you, Diana

A. Ford issued a TSB on this problem. It seems the Mass Air Flow Sensor gets contaminated and will not operate correctly. I quote from the bulletin:

"MAF sensors can get contaminated from a variety of sources: dirt, oil, silicon, spider webs, potting compound from the sensor itself, etc. When a MAF sensor gets contaminated it skews the transfer function such that the sensor over-estimates air flow at idle (causes the fuel system to go rich) and under-estimates air flow at high air flows (causes fuel system to go lean). This means Long Term Fuel Trims will learn lean (negative) corrections at idle and learn rich (positive) corrections at higher air flows."

This malfunction may or may not throw a DTC (Diagnostic trouble Code). If it does, the possible DTC's are: P0171, P0172, P0174, P0175 may be stored in memory.

I would make this the next thing I have checked out.

Information provided courtesy of ALLDATA