Manifold pressure reading in correctly

[Charlrv9]

Why at 7500 feet today my RV 9 with o- 320 lycoming
skyview manifold pressure reading 28 inch rpm reading 2400
I quite sure this is incorrect I pull throttle back and a bit and then it come right 24/24 not sur what going wrong
Dynon can you help
Thanks
Charles Mifsud

 

[kellym]

You can check MP on the ground. With engine not running, it should within about 0.5" of the altimeter setting.
Once you start the engine, it should be under 12" at idle, preferably under 10". If it is above 12-15" at idle, you have a leak in the system. Also, on take-off roll, if near sea level, it should be about 1" less than altimeter setting.

 

[mmarien]

The 28" at 7500' doesn't make sense though even if there was a leak. I fly WOT and checked a couple of flights at 7500 DA. I have a MAP of about 22.2 to 22.4. Using the rule one inch for every thousand feet: 29.92 - 7.5 = 22.4. So the best you should get at that altitude (not boosted) is 22.4 or so.

Are you using the 12V power from Skyview for the MAP sensor? or are you using another source? If the input voltage for the sensor isn't regulated it may give you different readings.

 

[Dynon]

The altimeter setting is the pressure that would indicate zero on the altimeter for your current atmosphere. So the MP only equals altimeter setting for sea levelish airports. Else you'd expect the observed MP to approx the altimeter setting minus 1" for every thousand feet of elevation.

Another way to test: Set your altimeter "baro" setting until altitude reads zero. In this case, your baro setting and your MAP should be close.