Rotary crank index offset question - Emtron

I have a 13-BREW engine and I'm having an issue verifying my crank index offset.

There is one mark on the stock pulley, which is -20 deg for the front trailing, and it also represents -5 for the front leading.

I can lock my timing to 0 deg, set the split at 20, and the mark lines up with my timing light at 0 deg offset. I can repeat this by locking the timing to 10 degrees, and the split to 30, and the offset is still zero.

When I check the leading things don't make sense to me. If I lock the timing to -5, I end up with an offset of -15.

I have verified the coils are wired correctly and I'm running direct fire. What am I doing wrong?

That mark on the pulley is for checking timing on the front trailing coil. Make sure the front trailing timing from the ECU is -20 degrees (by whatever combination of leading/trailing timing necessary) when you check it. The front leading coil would only line up with that mark if you set its timing to -20 degrees.

If you've got a paint pen and you're not afraid of math, it's also possible to add another mark to the pulley for checking timing at other numbers. It's probably more useful to know if the timing is accurate at +10 or +40 degrees than at -20 degrees.

Thank you Scott, for some reason the factory manual lists the same mark as -5 deg for the leading, which should be ignored in this instance then? So going forward I should only measure using the trailing or make another mark. Thanks!

"for some reason the factory manual lists the same mark as -5 deg for the leading".

I dont know how it is worded in your manual but it seems like you might be interpreting it wrong. The FD only has a single -20 mark on the trigger wheel, so you can only really use that mark for checking the #1 trailing spark. The earlier 13B's had two separate marks, a -5 and a -20.

I've attached the factory manual image. I guess I am looking at it wrong?

A single mark is a single angle. The s5 and earlier had two marks on the crank pulley. Most of the factory rotary crank pulley are sized such that 1mm circumference is equal to a degree of angle if you wish to measure forward of that mark (closer to leading idle or idle timing for a ported motor).

So to be clear then, the FSM is incorrect for the S6 since there is no separate mark and conflaits the leading and trailing on the single mark.

I agree with your previous comment, you were looking at it wrong. If you read that page very carefully it says you should connect the timing light to the front trailing coil. It never instructs you to check timing for the front leading coil, I suspect that -5 deg number is provided for reference only. The OEM setup is wasted spark for the two-post leading coil which would flash at -5 and also at +175 on the pulley.

Okay, thank you. My brain has gone galaxy with this, lol.