I hate the internet... anyway were was i
On most mk1 it doesnt throw any lights on just puts the car into limp mode to protect itself. The way to trick the egr sensor is to reroute the thin pipe from the egr valve to the egr sensor.
1)unplug both pipes from the egr sensor (it should be near your brake reservior,thin black thing which will say ford on n have two little pipes running from bottom)
2)make sure both pipes are blocked up coz hot exhaust fumes will come through n obv not good lol
3)take the thin pipe off the top side of the egr valve itself, should be same size as the two youve just unplugged from the sensor
4)plug the pipe from egr valve into the left channel off the sensor
Ive only read this so dont have personal experience with how well it works but from what ive been told it should work unless your egr sensor is dead. (inwhich it wouldnt matter if you blocked the egr valve coz the ecu would still realise the sensor dead n put it into limp)
The weird high pitch noise could be a split in any of the pipes i mentined above or the intercooler pipes as there are all under pressure when engine is runnin
Sorry for the length of post pal