Hello mate
Just kidding about disconnecting the Rev counter, just stalling for time, while i found 'enlightenment' ( ie help ). The rev counter is just an output of the ecu, and in no way effects operation, so ignore this!
First off lets get to the problem. When you get to 5500RPM, does the engine 'cut' like its reached the limiter, or does it start to misfire? If it starts to misfire, read the post further down. If not, read on!
All the data for engine speed comes from the pickup sensor in the bottom of the gearbox bell housing. This could be dirty or faulty and giving false info to the ECU, so check this first. First check this is sitting properly in its 'hole' in the housing, and check that the cover plate is properly securing it. Also when checking this, take out the sensor and carefully clean the face of it wiht a tissue or soft cloth ( NOT sandpaper or a wire brush ), then smear a little copper grease (not too much) across the face before refitting.
Next follow the lead from the sensor round the back of the engine til you get to a little round 'multiplug' this connects the sensor to the main ignition wiring loom. Check this is not loose and all the connections are okay. If anything appears amiss here, try getting holds of another gearbox sensor that works, fit it and see if there is a difference. If not, go insde the car, undo the cover plate, pull out the ECU ( CAREFULLY ) and pull off the multiplug connected to it. There should be numbers on the face reading one to twelve next to respective pins. look for pins 5,6 and 8, which are the pins for the wires from the sensor, and check their not damaged. Finally, carefully with a screwdriver, prise the back cover off the multiplug, and look at the back of the pins to check the wiring connections arent loose ( DO NOT remove the pins from the back and get em mixed up!! ). Try this little lot 1st, if this dosent work, according to the 'Ford supplementry manual for the RS1600i' the problem lies wih your ECU; which is bad news im afraid.
Any questions reply here or email me
streetsleeper@amserve.com
Cheers
Gray