So far nobody has an explanation for this one.

The "check engine" light on my 91 Ranger came on some time back. The
truck did not run any different after the light came on than it did
before the light.

The self-test just gives Code 22 on KOEO (both O & C codes). Every
reference that I have found says this is "MAP/BP sensor out of range".
But Ford says the 1991 Ranger XLT 3.0L v6 does NOT even HAVE a MAP
sensor.

Yes, I know that it has an MAF sensor instead thought nobody has been
able to explain how a Mass AIR FLOW system can replace a Manifold
absolute PRESSURE (ie vacuum) based system.

So what is causing the computer to read the code 22? And what can be
done to correct the problem & turn the "check engine" light off again.

And, BTW, yes I have reset the soft code storage. And know that the
reset worked because immediately after having done the reset the KOEO
test gave 22  22  1  11 indicating that the C (soft code) storage had
been cleared.

On the same topic, can anyone tell me for certain where the
microprocessor unit that generates the self-test codes is located on
the truck? I have 3 different answers so far but none appear correct.

While we're at it, how exactly does an MCU differ from a PCM or an EEC
or an ECU. Are they all the same unit or different physical modules?

TIA!

Bob W
Miami FL