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Trigger calibration without a timing light


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My engine doesn't have any timing marks that I can find.  I do know, however, where TDC is relative to the first tooth after the missing tooth (60-2 configuration on the crank).  If the first tooth after the missing tooth is, say, 50 degrees BTDC, then do I enter 50,  -50, or 310 (360-50) in the 2nd field in "Set Base Timing"?

ECU is Force GDI if it matters.

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Yes, it will be -50 deg if the cam tooth has already past the cam sensor at that point or 310 if the cam tooth hasnt gone past its sensor yet.  (i.e these are effectively the same crank position - just one will be compression stroke and one will be exhaust stroke).

Note I still strongly suggest you paint a mark on and verify yourself though.  It doesnt need to be highly accurate, you can usually feel it out pretty well with a just screwdriver poked down the spark plug hole and rock the crank back and forwards until you are at the highest point, then paint a temp mark on the pulley with a white marker pen or similar.

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Rather than trying to feel when the screwdriver stops moving, you can also set it deliberately 5-10* past tdc, mark this point on the crank with something temporary, put the screwdriver in until it hits the piston, then hold it really tightly in that spot. Rotate the engine around 90% of a rotation until it just touches your screwdriver then mark that point as well. TDC will be exactly half way between these 2 points on your crank, so just a simple measurement.

This process avoids trying to guess where true TDC is during the 3-4* where its pretty much not moving at all. Its better if you can bolt something into the spark plug hole and then *by hand* bump then engine into it in reverse then forward to create the 2 marks, but holding a screwdriver really steady doesnt require a "special tool" like a plate welded to a long bolt, and gets you really close.

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