Good suggestions, thanks. Have checked the bolts they are ok, no work has been done on the car it just stopped one day. Air gap sounds likely, the CPS is known to be good, it has been tested on a multimeter and works fine but doesn't read AT ALL when the multimeter is connected to it and its bolted to the block. I know the ECU needs the correct signal to work properly but my CPS isn't giving out any signal at all let alone the wrong one
Would thrust washers wear enough to alter the gap so it wouldn't read at all?