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Manifold pressure


Rich

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While going over the numbers for the 912ULS engine I noted the MP should be in the 18-28 HG range.

Since new my engine operates between 12.8 and 14 HG.

 

The engine runs fine but now I'm concerned that the wrong pressure sending unit was installed in the AC.

 

Thoughts appreciated

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While going over the numbers for the 912ULS engine I noted the MP should be in the 18-28 HG range.

Since new my engine operates between 12.8 and 14 HG.

 

The engine runs fine but now I'm concerned that the wrong pressure sending unit was installed in the AC.

 

Thoughts appreciated

What does it read when the engine is not running?

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What does it read when the engine is not running?

Tom,

 

I have never looked after engine shutdown.

 

Roger,

 

Where would be a good place to start to look for a leak and could you tell me where the sending unit is located?

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Maybe. Though I don't recall PSI creeping into the discussion.

 

I don't recall ever seeing a MP gauge showing anything other than inches of mercury:

 

R22_MP.jpg

 

Roughly what it would show at SL on a standard day.

 

The psi conversion might come into play by the coder of a flat panel display.

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Sure.

 

But for now, I think I'd advise that we all think in inches of mercury, since its still the norm for aviation.

 

The conversion factor seems correct.  If unconverted data is being displayed there is no other way to solve this this so it will display inches of mercury than to think in both psi and inches of mercury and add the conversion prior to displaying the result.

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When I was flying certified aircraft with a constant speed prop and manifold pressure guage, 23/23, 24/24, 25/25 were commonly used settings for manifold pressure and rpm with manifold pressure in inches of mercury.  13.5 seems really low unless there is something different about how or where it is measured.  It does sound more like a psi measurement even though the guage says inches of mercury.  IDK?

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You never did say what it is with the engine off. If it is up near 30 then it is not the sender, but a leak in the line, I did notice you said new engine, but I wouldn't expect that the MP sensor would be changed at an engine change, unless it was specifically requested to be changed.

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Hi Tom,

 

I did mention that I never looked at it with the engine shut down.

I'm not close to the airport so I'll need to wait for the next trip.

 

The engine is the engine supplied with the aircraft when new (2012). Approx 190 TT.

I just spoke to Zack at Tru Trak and he's researching as I write this post.

 

I'll post the findings, probably later on today.

 

I just got the call and they want to know what it's saying with the engine off as you suggested.

It'll have to wait until I get out there.

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Bob,

 

Close but a little low.

 

I went out to fly today and noting the manifold pressure with the engine off it read 15.5.  Baro pressure at the field was 30.07

At 3K feet the manifold press on the Tru Trak unit read 12.5 @ 4750  RPM.

I need to relay this info to Tru Trak on Tuesday.

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Just a reminder that barometric pressure and altimeter setting are two different things.

 

At Denver, you can have an altimeter setting of 30.00 in/hg and barometric pressure of about 25".

 

I assume field elevations in PA are usually less than 5,000', but at anything other than SL the difference still has to be considered.

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Thanks for all the replies.

I'm just an "A" personality when it comes to my airplane. Even though I know all is well with the engine, I want the readouts to be correct.

May be it's a simple fix. I'll know on Tuesday and post what Tru Trak has for a remedy.

Thanks again.

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A call this AM to Tru Trak.

The EDM must be removed and sent in to the shop as there isn't a remote sending unit. The sensor for the MP is located within the EDM.

 

I'll be waiting until the snow flies again to remove and ship the unit.

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  • 1 month later...

I apparently need to venture out of the Autopilot sub-forum.  :)  The sensor is on the engine data module board itself, no remote sensor.  It sends a signal over to the screen.  Units and arithmetic on the signal are done in the software of the screen.  I doubt it's a software issue, otherwise we'd see this all over the place.  I do suspect this is a sensor problem.  There could be damage to the sensor's diaphragm.  We'll check it out when we get it!

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