Mercury 40hp fourstroke EFI, 2002 ELHPT

by Shane DeGeeter
(Iowa)

Engine stumbles just off Idle. When hooked to diagnostic computer, the ignition timing sits at around 2 to 3 degrees advanced. Once throttle is applied, the timing starts jumping all over the place. It will jump around from -4 to +33. I can feather it to get through it sometimes and then at roughly 2500 RPMs the timing sits at around 7 degrees advanced. I understand these numbers are correct, but what is causing this. Is it the ECU alone or is there a sensor input that isn't telling the ECU correct information?

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