If you remove the pulley be sure to use adhesive between the die Glocke (the bell) and the pulley. That step is not in the pdf but is in the oem service manual. Pay real close attention to the locating tab. PP have ruined brand new HES units from incorrect assembly.
I'm kinda surprised that any issue with the HES would cause "rapid firing of the injectors". Are there any signs if interrupted power on the dash? RID flashing on/off?
- The ignition switch is a unified with a sub-harness that has know issues along with solder point on switch failing.
- The ss switch might be flashing the power to the Motronic.
- Relays in the relay/fuse box have been known to seize or develop high resistance
- Power wire for the O2 sensor grounding out?
- check where the main wire harness passes close to the bottom of the battery box- sharp edge there
- kill switch may have high resistance. Can be temporarily by-passes (I think)
- remove tank and check the batch of harness connectors, check for steady power in from the rear from the ss switch (refer to wire diagram) Have seen this one over-heat, melted insulation, probably from someone grounding ss switch in bypass (1100).
- remove each injector connector, inspect for corrosion, if present repair the rubber weather boot