miller92063,
The Powertrain Control Module (PCM), or main computer in our cars has what is called a Failure Management Effects Mode (FMEM).
The PCM relies on readings from several sensors to provide it with information regarding operating parameters of the engine. If the PCM detects any sensor input that is out of range (like the MAF, ECT sensor, ACT sensor, O2s, etc.) it is designed to go into FMEM so the car can continue to run.
In the mean time, it throws a trouble code and turns on the check engine light so you know that something is up.
In FMEM the PCM compensates for sensor inputs that are out of range. For some sensors it does this by substituting an average value for the particular sensor that is stored in ROM in the PCM. For the MAF, however, it uses a combination of real-time readings from the throttle position sensor (TPS) and the engine RPM to operate the engine.
And, if you've got a bad MAF to start with, your engine just might run better using those substituted values.
PS) This information is from the book "Ford Fuel Injection and Electronic Engine Control", by Ford Engineer Charles Probst.
, didn't bog hesitate or anything. I'm done working on it for the day, but would like to have an idea for when tomorrow comes.
