I have a '92 5.0, and it has been having acceleration problems above 3500RPM. I found out that when I disconnect the MAFS it accelerates much better. So, I assumed that the MAFS was the problem. I tested the AB terminals while the engine was running and got 13.8V, and the CD terminals showed 0.85V. According to Chilton's this is means the sensor is getting power and is within spec. Does anyone know what else would cause the engine to run better with the MAFS disconnected?

 

It may be within specs as far as voltage goes, but that won't tell you if it's dirty or somehow damaged. First thing I would try is cleaning the MAS. Just remove the sensor and spray the two tiny wires with MAF sensor cleaner (buy it at any parts shop like Napa, Auto Zone, etc.) You can also check the vontage on the signal wire. It will read btween 0 and 5v. Higher voltages means more airflow, so that would mean that the MAF thinks more air is flowing into the engine, usually associated with an increase in speed / power. It may be beneficial to check the voltage while accelerating to see if it increases as it is supposed to.

If the MAF is screwed up, then it could run better with it disconnected. When disconnected, the MAF senses the "failure" and uses a different startegy / tables to determine how much fuel to deliver. So that means that the default table is basically better, which means the MAF or MAS must be screwed up.

 

The thing is, that my old MAFS was still under warranty so I got a replacement at O'Reilly's. The replacement is a rebuilt MAFS, but so was the previous one. I got the same readings on the new one as the old.

 

Did they replace the housing, did the replace the actual sensor, or both? I would have them replace both. Either way, I'd still check the voltage from the signal wire while driving to see if it's reading voltage correctly.

You don't have any sort of chip installed do you?