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  View original topic: Grounding sensors through PCM...
nbuscemi Sat Nov 10, 2018 3:13 pm

This is one of those "I should have known better" stories...

Even though I've had a lot of experience with EFI it has always been diagnosing or repairing a factory setup. Replacing the factory carb with a home-brewed fuel injection setup has certainly been a learning experience. Megasquirt specifically instructs to use the PCM ground for all sensors. When I wired up the ECT (engine coolant temp) or in this case Cylinder Head Temp it was after everything else was already in place. Not thinking, I wired the CHT / ECT sensor to the engine ground. For the life of me I couldn't figure out why my engine temp data was so jumpy ( see datalog below)



After connecting the engine temp sensor ground directly to the PCM sensor gorund pin (same as the IAT sensor) there was a world of difference (again, see below)



Nice and smooth!

So take this as freindly advice or something to double check is you are getting erratic sensor signals.

-Nick-



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