TDC Reference Angle for LS vs Northstar

[gmh308]

My ECM guy ( https://gmtuners.com/ ) sent this service manual info:



I was wondering how people were installing the trigger wheel on-- or simply seeing-- the 13th tooth, or any tooth other than the 14th tooth, *WITHOUT* the ECM setting a P0016. The answer is that the tolerances for P0016 are wide enough that the crank trigger wheel can be off almost two whole teeth in one direction, and more than two whole teeth in the other direction before the ECM will set P0016.

A less obvious consequence is that the ECM still triggers spark based on the 14th tooth. So someone who installs the crank trigger wheel on the 13th tooth has BUILT THEIR ENGINE such that it will inherently have a SIX DEGREE TIMING RETARD vs the values in the tuning software.

That is, base timing is 6 degrees retarded vs where they think it is.

Great information thankyou for sharing! That's a wide spread for production errors via crank/cam tolerances stack that are covered for.

Cam teeth are 16.36 degrees crank each, or 2.7 crank reluctor teeth each way covered.

The +/- 1.5 or 2.5 (cam - checked notes - was actually +/- 0.75 deg) I mentioned on LS1 tech for P0016 was divined using a crank/cam sim on a E38 & advancing/retarding the cam signal. I must revisit this and pay more attention to the error window.

FYI measured 58X wheel teeth & gap size, not symmetrical - tooth 4mm, gap 5.5mm, & that doesn't take into account the radiused edges on the tooth.

[The Dark Side of Will]

Great information thankyou for sharing! That's a wide spread for production errors via crank/cam tolerances stack that are covered for.

Cam teeth are 16.36 degrees crank each, or 2.7 crank reluctor teeth each way covered.

The +/- 1.5 or 2.5 (cam - checked notes - was actually +/- 0.75 deg) I mentioned on LS1 tech for P0016 was divined using a crank/cam sim on a E38 & advancing/retarding the cam signal. I must revisit this and pay more attention to the error window.

FYI measured 58X wheel teeth & gap size, not symmetrical - tooth 4mm, gap 5.5mm, & that doesn't take into account the radiused edges on the tooth.

Interesting detail about the tooth and gap widths.

I think the P0016 was implemented to catch *assembly* errors, like installing the cam a tooth off, rather than production errors. I'm sure with production tooling, GM can hold the installation tolerance on the trigger wheel to less than a degree. Also, since error in trigger wheel position translates directly to timing error, which acts on emissions compliance, GM does a very good job of installing the wheels. Trust but verify.

How good a job does anyone else do? Who knows? Always check.