Can't find a good picture of an OFAC sensor at the moment - but this auction has the correct one:

http://cgi.ebay.co.uk/fiesta-turbo-o...ayphotohosting

There's a couple of easy ways to tell - firstly the shape is different - XR2i ones are rectangular whereas the OFAC ones are wider at the bottom than the top. Second;y the OFAC ones have a part number on a sticker - white writing against a black background. The XR2i ones have a moulded part number.

Ordinary XR2i MAP sensors cannot register boost. I believe they read the same at vaccum but that's it. Consequentially an OFAC ECU will idle with a XR2i MAP sensor but as soon as it comes on boost the mixture will lean right out and you could melt a piston.

Here's a slightly better picture of one borrowed from www. FiestaTurbo.com