ok sorry its been a while since ive been arsing around with fiesta turbo's, what youve heard is right there is two types of map sensor for the efi management, ofab and ofac, these are the two different ecu brains that ford used the ofab is found in the earlier ones ie g reg and h reg and the ofac on j's and k plates, if that helps. this is usually written on the ecu if i remember, the ofac one is kind of squareish, black, and has the map vacuum inlet and the multiplug on the bottom, and the ofab i think the vacuum pipe goes into the front of it, MAP sensor is for sensing whether the engine is on vacuum or on boost and what the kpa/bar/psi the engine is on, this dictates the fuelling for the event, on the map for the ecu it will have map bins and a ve table(volumetric efficiency) basically its a table with the revs on the left hand side and kpa along the bottom, so if the engine is a 2000 revs and at 2psi of of boost it will inject x amount of fuel.
so if your still with me.......... if the map sensor aint reading correctly, your fuel is more then likely gonna be well out, causing shit running of car.