Questions and Answers

Ford Explorer Mis-Fire Q. 1994 Ford Explorer Limited 4.0 liter automatic transmission, 55,000 miles. Problem: after highway driving at 65 to 75 MPH, usually after about 60 miles, it develops a miss. This is around 2,600 RPM, in overdrive. Fuel mileage gets very bad, black smoke from tail pile, loss of power, intermittent check engine light.

We just replaced the mass air flow sensor, and this was no help. Same problem repeated, no codes were stored via check engine light, though it was on for a long time. I can avoid the problem by putting it in drive, and running the car at about 3,500 RPM, less missing, but still bad fuel mileage. One Ford dealer wanted to replace all sensors, but I want a diagnosis prior to wholesale parts replacement. Could this be an O2 or HO2 sensor problem, or a fuel pressure regulator problem?

By the way, it is difficult to recreate, you must drive it at least 60 miles at highway speed to get the problem. Everyone I have taken it to, including a dealer and two top notch independents, gets different codes or no codes, it is very confusing.

A. I'd like to know what some of the codes were. It would help me point to a probable cause.

But from what I see, it looks like the spark plug wires are breaking down due to the heat. I would suggest replacing the ignition wires and see what happens.