Strange MAP readings

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Joined: Tue Jul 02, 2013 8:04 pm

Strange MAP readings

Post by mlwynn »

I have been through a really frustating round of getting my engine to operate correctly. It is now running smooth and strong but I still can't make heads or tails of MAP readings. The strange reading have really complicated the process of finding why my engine didn't want to run smoothly.

IO360M1B Engine
Dual Plasma III Ignition
AFP FM 200 Injection system
GRT EIS 4000 and manifold pressure sensor.

On the ground, at idle, I cannot get the MAP reading below 12-13 inches. This is with the engine idling smoothly and taking throttle without problem. It goes up with adding throttle and indicates 29.9 with the engine off.

There are two read-outs: one from the EIS EFIS and a second separate indicator that comes from the Plasma Ignition. I would have thought there was a problem with the pressure sensor except both systems match.

Gets weirder. When flying, pull the throttle back and you see 9-10 inches. Once again, the engine is running fine. This is the reading I would expect to see at idle on the ground, and seems like the correct reading in the air.

So, why would it be different in the air and on the ground? I searched for a long time for an induction leak. Found one: a faulty sniffle valve. With that out of the system and the hole plugged, no change in the MAP readings.

Does anyone have an explanation for this?


Michael Wynn
RV 8 Phase I
Livermore, CA
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