how does milling the cylinder head affect the valve timing??

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Originally Posted by My88isGREAT

You don't need to jumper anything to check timing, just hook up timing light to #6 plug and see if it is running at 10 before TDC

You're wrong... On both counts. You can only use #6 on the GTE for timing as it runs a wasted spark setup, not so on the GE; You MUST have the engine at normal operating temperatures, no critical diagnostic codes present, and you must jumper TE1 and E1 so the ECU does not adjust the ignition timing and sticks to the programmed map explicitly.