One of the simplest components in the Rover SD1 Fuel Injection System is a common resistor measuring 6800 ohms or 6.8k ohm. It is a sturdy item encapsulated in resin with 1/4" spade connectors because Rover decided to fit it inline with a single connection from the coil to the ECU mounted virtually in free air alongside the air flow meter.
This trigger resistor is connected in the line between the negative side of the coil to pin No 1 of the Electronic Control Unit (ECU) and by virtue of the pulsing signal on the negative side of the coil informs the ECU that the engine is running. Its purpose is two-fold.
1 As a voltage drop input component to ensure the ECU receives the correct level of input voltage.
2 Protect the ECU from any excess induced voltage that might otherwise occur at the ignition coil.
Interestingly, it appears to have picked up three different descriptive titles depending upon which Rover document one reads. Over time, it has been variously referred to as either a Trigger, Ballast or Inline Resistor.
The word "Ballast" is most misleading as that is usually a term used for a resistor employed to reduce the operating voltage at an ignition coil. The word "Trigger" is a slight misnomer in that it implies some sort of active function which it does not possess. Thus the word "Inline" appears to best describe its use and function. But then, 20 odd years after all the books have been written, it is anybodies guess as to what the designer of the system really had in mind.
One thing for sure, is that the component was almost certainly included for the purpose of protection and it would be unwise to omit it.
Please advise of errors and omissions.
Rover SD1 Efi Archive - Trigger Resistor
The Diagnostic Challenge Continues
This above article is one of fifteen or so presentations on the key components making up the Electronic Fuel Injection System fitted to Rover SD1 Vitesse and Vdp Efi.
Pulling all these components together is the Efi Operations, Test and Instruction Manual enabling Home Enthusiasts to better understand its Purpose, Function and Maintenance.