Manifold Pressure test

RV8iator · #1 08-31-2009, 07:08 PM

What's an easy way to test my manifold pressure gauge to see if it's bad or if I have a leak in the tubing.
At rest it seems to read about right, however, when I pull to idle on downwind, about 2300MSL here I my home field, the MP is going to about 20 inches. I know it should be lower than that but don't know if its an indicator or tubing leak.

AlexPeterson · #2 08-31-2009, 08:45 PM

Jerry, since you aren't at too high an altitude, you can verify your (approx) sea level MAP gauge reading by dialing your altimeter until it reads 0 msl. The resulting barometer (kollsman) reading should match your MAP gauge with the engine not running. But, it sounds like you believe that is ok.

If you disconnect the tube at the engine, you should be able to suck a reasonable vacuum, cork it with your tongue and see how quickly it leaks, if at all. Someone else could be in the cockpit monitoring MAP.

Your flight idle MAP should be something in the neighborhood of 6 to 10"?

Noah · #3 09-01-2009, 10:48 AM

Would be easy to build a water manometer with a piece of transparent tygon or nylon tubing, you'd be able to make just about any pressure you wanted with a long enough piece of tube. Juts make the tube into a U shape and the difference in height from one side to the other is the vacuum pressure (in inches of water). You would need to convert this to inches of mercury to check your gauge. Search the archives on manometer or U-tube manometer and you will find detailed descriptions on how to set this up.