I have recently inherited a 94 F150 with a 4.9 that I plan on using as a light-duty tow vehicle. It was running quite poorly, but the routine tune-up items seemed to have solved most of the issues (plugs, wires, cap, rotor, air filter, ISC cleaning).

I still notice a hard shift between 1 and 2, and also some shudder at fast highway speed that occurred only on one occasion. There is also a slight hesitation at times when tipping-in from a stand-still.

The ECU is also complaining that the o2 sensor is running rich, and that the MLP sensor is not at expected voltage.

I am planning on getting the tranny, tc and diff fluid flushed, but I am not sure how to proceed with the MLP sensor.

I have cleared the codes from the ecu, and after driving for 20 minutes the CEL came on. For some reason, both of these codes (173 and and 634) are present. Does it sound like I truly have a bad MLP sensor, or does it sound like I have a wiring fault?

Once the tranny issues are out of the way I'll deal with the o2 issue.

 

Ford's MLP sensors have a deserved poor reputation. I'd just replace it.

Steve

 

I agree, replace the MLPS.

Codes can't tell the difference between a bad sensor or bad wiring. It could be either, but in this case I'd bet that it's the MLPS. They have a high failure rate.

 

Thanks for the advice, will do.