Haltech IG5 - Manual (Page 85)

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APPENDIX D ROTOR PHASING
On engines which are operating a distributor to deliver spark, rotor phasing must be
considered when setting the trigger angle and the physical position of the trigger device in the
distributor. If the rotor phasing is wrong, there may be a considerable gap for the spark to
jump between the rotor and the cap terminal when ignition occurs or worse still, it may be
delivered to the wrong terminal and fire the wrong spark plug.
When setting the trigger angle (i.e. setting the timing relationship between the trigger input
signal and the engine crankshaft which must be between 60 and 100 degrees BTDC) avoid
rotating the distributor housing from its original position to achieve the desired timing. The
best method to achieve the required timing is to alter the angular position of the plate on
which the sensor is mounted in its relationship to the distributor body.
Note: The original mechanical ignition advance mechanisms must be locked so
the ECU will see a fixed angle between the crankshaft and the trigger.
Checking rotor phasing
An example of checking correct rotor phasing is given now.
a) Assume the trigger angle is set at 80 degrees and the IG5 is mapped to give an actual
ignition advance range of 10° to 40° BTDC.
b) The midpoint between 10° and 40° is 25° BTDC (remember these are crankshaft degrees
not distributor degrees.
c) Crank the engine to 25° BTDC (the midpoint).
d) The rotor button should now be pointing directly at the centre of one of the distributor cap
terminals.
Correcting rotor phasing
If, when checking as described, the rotor is not pointing directly at the centre of a distributor
cap terminal, figure out if altering the trigger angle can be used to correct the error. If for
example the rotor button is too far advanced by say 10° of distributor rotation the distributor
housing could be rotated 10° degrees in the direction of the rotor rotation and the trigger angle
altered to 60° (ie. a change of 20 crankshaft degrees or 10 distributor degrees). The rotor
button would still be in the same angular position when the spark occurs but the distributor
cap would be 10° further around bringing it into proper alignment with the rotor. If the
phasing cannot be corrected by altering the trigger angle it will be necessary to alter the
internal timing relationships within the distributor.