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Old 08-21-2022, 09:00 PM
Berchmans Berchmans is offline
Join Date: Nov 2009
Location: Anchorage, Alaska
Posts: 469
Default Manifold pressure drop

I have a manifold pressure question. I seem to have experienced a drop in manifold pressure at full power. Some background.

Engine - YIO360MIB
Total time - 280 hours

The engine is developing full power and performing normally. Normal temps. oil pressure, etc. at lower power settings the pressure seems to be reflecting normal levels. Fuel flow also normal.

I have inspected the system and can find no leaks or issues. Here in Anchorage we have been experiencing much wetter weather than normal and was wondering if that might be the culprit. I did replace the sensing unit about 50 hours ago.

Burke Wick
Flying RV 8
Anchorage, Alaska
VAF Dues Paid for 2022
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Old 08-22-2022, 08:10 AM
mahlon_r mahlon_r is offline
Join Date: Jan 2005
Posts: 1,086

Rough MP gauge check: it should read barometric pressure with the engine not running.
Good Luck,
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
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Old 08-22-2022, 08:22 AM
BillL's Avatar
BillL BillL is offline
Join Date: Sep 2007
Location: Central IL
Posts: 6,850

What Mahlon said first,

but a consideration - A 10Friend had an issue with his MAP and we found that concentrated black fuel goo got up in his MAP sensing hose and was affecting the reading on startup until warm and the goo softened.

I am not sure how this would effect your observation though.

Only an air filter restriction would come to mind if the MAP is reading Baro before start. If top speed is exactly the same, then this is no factor.
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Old 08-22-2022, 08:55 AM
lr172 lr172 is offline
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 7,754

Originally Posted by Berchmans View Post
I have a manifold pressure question. I seem to have experienced a drop in manifold pressure at full power. Some background.
Verify that the throttle plate is fully opening when the black knob is all the way in, as if it is not it would cause a MAP drop at what you think is WOT.

I recently did some work for someone and the nut was so loose, that the serrated interface was just about to allow the throttle arm to start adjusting itself.

N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
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