Just purchased a used 90xp with the Perkins . The tach goes into test mode each time its started and stuck on hours cannot switch to rpm. The auto feed does not seem to be working right and the tach is IEC . Please advice
I don't have specific info on your model but most autofeed systems work by sensing engine rpm. This can be done with a magnetic sensor at the flywheel or a signal from the alternator.
Since the Tach is not reading it's likely the reason autofeed is not working.
See if you can source a schematic specific to your model/engine.
Start with testing the signal from the rpm sensor with a DVM.