Manifold Pressure Gauge

[merrja]

Today my MP gauge decided to lay down.   We checked the line and there does not appear to be a leak or crack in the line.   The gauge shows 25" when the engine is running at idle.  Any ideas or recommendations for a replacement?

 

Thanks!

Jim

[Marauder]

2 minutes ago, merrja said:

Today my MP gauge decided to lay down.   We checked the line and there does not appear to be a leak or crack in the line.   The gauge shows 25" when the engine is running at idle.  Any ideas or recommendations for a replacement?

 

Thanks!

Jim

Jim -- Was the MP gauge in combo with the fuel pressure gauge? If so, Guitarman was selling one. Looks like this:

 

Another way to go is install an EI MP gauge. I have one in my plane. Works great.

 

[merrja]

1 minute ago, Marauder said:

Jim -- Was the MP gauge in combo with the fuel pressure gauge? If so, Guitarman was selling one. Looks like this:

 

Another way to go is install an EI MP gauge. I have one in my plane. Works great.

 

Thanks for the reply, It was the combo gauge.  It's only been in there since 1968! 

[Marauder]

Just now, merrja said:

Thanks for the reply, It was the combo gauge.  It's only been in there since 1968! 

I would check with Guitarman. I sold him the gauge you are seeing in the first picture. If the marking are the same, it would be an easy swap. My road down the EI path was because a certain unnamed shop destroyed my tach by installing a replacement cable that was too long. Repairing the tach was more expensive than replaceing it with an EI tach. I flew around like this for a bit until I replaced all 3:

 

[Bryan]

I am replacing mine with an JPI EDM-900 next week. My stock one will be available soon.

[carusoam]

Idling and showing 25" is typically what happens with a leak in the line from the engine to the gauge...

My 65C MP gauge had the weep hole on the 1/8” (?) soft aluminum line to the back of the instrument.  It cracked open at the hole the crack isn't very noticeable.  But if you grab for it while flying, it will probably come off in your hand.

The weep hole is calibrated and can be drilled using ordinary tools.  There are probably a few fittings that can leak from the cylinder to the firewall to the instrument.  The soft aluminum tube can have a 50 year lifespan.

It is impossible to set the power without an MP gauge...

Is this something that has happened recently?  Or has the gauge been failing for a while?

Best regards,

-a-

[merrja]

2 hours ago, carusoam said:

Idling and showing 25" is typically what happens with a leak in the line from the engine to the gauge...

My 65C MP gauge had the weep hole on the 1/8” (?) soft aluminum line to the back of the instrument.  It cracked open at the hole the crack isn't very noticeable.  But if you grab for it while flying, it will probably come off in your hand.

The weep hole is calibrated and can be drilled using ordinary tools.  There are probably a few fittings that can leak from the cylinder to the firewall to the instrument.  The soft aluminum tube can have a 50 year lifespan.

It is impossible to set the power without an MP gauge...

Is this something that has happened recently?  Or has the gauge been failing for a while?

Best regards,

-a-

Thanks for the reply.  It just happened today

[carusoam]

When this happened to my C, I called the factory and met a guy named Bill Wheat on the phone...

Bill explained the routing and the weep hole in the line between the engine and gauge.  I knew of the weep hole from aviation and automotive training.  In the older planes it is a common piece of plumbing so there isn't an obvious part number for it.  

When trying to buy the part, the MSC sent me the closest thing they had.  Which was nice but I would have needed a new plane for it to fit...

The size and location of the weep hole are just a note in the instrument drawing for one of the 60's planes (CDEFG).  The note is missing from the C's drawing.  The parts manual for the F is a likely place to find the details.

if your line has a leak like mine did, it should be an obvious kind of problem like a loose fitting or cracked/broken tube

See if that helps.

This comes from the usual PP knowledge, but with the aid of Mr. Wheat.

If you need the dimensions for the weep hole, I can probably find it in my notes from the conversation...

If you have a few spare AMUs I hear the JPI 930 is pretty nice...?  

Note: I later found out who Mr. Wheat was. His signature was on the AW page in my plane's first log book. 25 years after he signed it.

Best regards,

-a-

Edited January 25, 2017 by carusoam

[bradp]

I was the one who picked up Guitarmaster nee Maurader's manifold pressure gauge. My gauge was acting funny in that it would read near atmospheric at baseline, seem to drop through the floor at idle and read 32" at full power. I think it's a calibration issue since I don't have a turbo :-). If it's not the gauge I'll send Marauder's to you for what I paid for it....


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[DonMuncy]

3 hours ago, carusoam said:

When this happened to my C, I called the factory and met a guy named Bill Wheat on the phone...

Note: I later found out who Mr. Wheat was. His signature was on the AW page in my plane's first log book. 25 years after he signed it.

Bill was a nice guy, a real character, and more knowledgeable about Mooneys than most anyone. It was a real loss to all of us when he died.

[Brandontwalker]

I have a MP/FP gauge sitting on the shelf in my office. Post your part number if you need it and we'll make sure it is a match.


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[Browncbr1]

This happened to me and it turned out to be a cracked flare inside the blue reducer fitting on the 1/8" aluminum line..   It did not appear cracked or broken until the blue but was loosened to inspect the flare.   

[Brandontwalker]

This is what I have:



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[carusoam]

Blue nut...    

Flaring the aluminum line without the proper tool is a challenge.  But, It is sooo soft it isn't very hard to do.

It is typical of compression fittings.  Everything has to be smooth and fit properly to hold a seal.

Anyone have a picture of the calibrated weep hole?

Nice pictures Brandon!  Where does that fuel vent go? I don't remember that one...

Best regards,

-a-

Edited January 27, 2017 by carusoam

[Brandontwalker]

Blue nut...    
Flaring the aluminum line without the proper tool is a challenge.  But, It is sooo soft it isn't very hard to do.
It is typical of compression fittings.  Everything has to be smooth and fit properly to hold a seal.
Anyone have a picture of the calibrated weep hole?
Nice pictures Brandon!  Where does that fuel vent go? I don't remember that one...
Best regards,
-a-

I have no clue about the fuel vent. There are certainly folks on here with much more knowledge than I on the subject.


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[Atalla]

This is an old thread but came across it searching about a pinhole in the MAP line I found trying to diagnose a MAP gauge not working.  Sounds like it's a weep hole as described here.  Here is a pic of it on my 62 C

[Atalla]

Also for others trying to diagnose their issues.  My MAP gauge stopped working and froze in position mid flight.  The small 1/8 line was loose in the fitting due to the flare breaking and it caused movement in the line.  That movement chaffed until it caused a leak.

[GLJA]

On 1/24/2017 at 6:23 PM, Bryan said:

I am replacing mine with an JPI EDM-900 next week. My stock one will be available soon.

That’s my route in my 74 F as well. But not in annual until March

[Hammbone]

You didn't say where you were located. I f you are in Denver there is nothing wrong with it

[carusoam]

Hamm,

everyone in this thread has a location posted under their avatar...

Looks like you might be using a cell phone to read the posts... the locations will be harder to find on a small screen.

when you get a chance add some detail to your avatar...

Best regards,

-a-

[Yetti]

On 1/26/2019 at 5:11 PM, Atalla said:

Also for others trying to diagnose their issues.  My MAP gauge stopped working and froze in position mid flight.  The small 1/8 line was loose in the fitting due to the flare breaking and it caused movement in the line.  That movement chaffed until it caused a leak.

Just fixed the same crack at the big to small line fitting at annual.   That's not how the hot air scat is supposed to be routed.   There is a mount for a big adel clamp on the foot well.

[Atalla]

Hmm that's probably why it's almost worn-through in a few places from rubbing.  Thanks will take a look at some diagrams and get it right.  I do have a seemingly rare/unpopular remote screen filter mounted on the firewall in that area.   Possibly previous owner moved things around because of that.  Now I gotta get to the bottom of this.