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CPS trigger position on flywheel

turbochimp

Member
Joined
Nov 2, 2011
I had a new motor put in 1990 740 by a succession of flaky mechanics (hence all the questions this week). One of them did not not install the flywheel at the correct orientation (aw71). I put the motor at tdc and then scoped the trigger wheel in place and made my best guess at the orientation offset (assuming it will be off in 45* intervals from original)

I updated MS (all stock LH sensor/harness setup with MS) for the new tooth position and it started right up. I think it's correct, but my question is: Can I be sure I have the correct trigger offset? Would it run if the CPS trigger was 45* early or late?

Hope that makes sense - Thanks!
 
Wow, you got lucky! Changing the Tooth #1 Angle in MS is trivial compared to pulling the engine to realign the flexplate. Assuming it was originally correct, the angle will shift in increments of 45deg. If the engine runs and revs normally, you most likely have updated the setting correctly. Use a timing light at idle to confirm.

Long ago, I think there were problems using certain ranges of Tooth #1 Angles in MS. AFAIK, those limitations no longer exist in the recent firmware versions.

There is still a recommendation that the Tooth #1 position be mid-stroke on the engine for easiest starting. During cranking, the flywheel speed is lumpy and slows down near the top of the stroke -- see the wavy Tooth Logger picture here (ignore that the edge is programmed incorrectly).

By aligning Tooth #1 position to mid-stroke, the tooth rate during cranking is fastest and it's easiest for MS to figure out that there's a missing tooth, versus just going extra slow near TDC. If it starts fine, then MS is detecting the missing tooth OK.
 
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