Manifold Pressure 0” at idle

[gwav8or]

 

Well I don’t like this. My F just came out of annual. Went to fly this morning and in start up the MP was showing 0” at idle. Ran up to 1900 RPM and the MP only came up to about 14”. Ran up to 2300 RPM and only got up to around 19”. When I pulled the throttle back to idle the MP actually went negative. Less than 0”.

 

Mechanic told me that the MP line was loose at one of the fittings so he reflared the line and reattached during annual.

 

What the heck?

 

I’ll upload some pics and a video when I get back to my computer.

EDIT - I can't attach a video, but when we removed the MP line from the firewall side it read normal.  I'm guessing it's a plugged MP line.

EDIT #2 - Adding pics

Sent from my iPhone using Tapatalk

 

Edited September 29, 2023 by gwav8or

[N201MKTurbo]

I would remove the MP line at the firewall on the engine side. If it doesn't read ambient pressure, then remove the MP line at the gauge, and see if it reads ambient. If the gauge does read ambient pressure, then remove the line from the engine and firewall and blow through it and see if it is clogged.

[gwav8or]

Yeah, when we removed the line it read normal.  When we were troubleshooting the baro was 29.99 and when the MP line was disconnected the MP was reading about 29" which I believe would be normal. Reconnect and the MP dropped to about 13" with the RPM around 1800.  So hopefully just a clogged line and blowing it out will fix.

[takair]

At least on the early E models, there is a tiny bleed hole in the line.  Was never quite sure if it was for pulsations, calibration etc.  However, he may have clamped that under an Adel or entirely eliminated it.  That alone might delay ambient when engine not running…

[PT20J]

There should be a small weep hole at the low point of the line to drain moisture.

[Dialed In]

Do you have a mechanical gauge or digital?

[Dialed In]

You can see the weep hole on my manifold pressure line at the top by a small dab of silicone if you zoom in. I think most are further down by the intake. 

[gwav8or]

40 minutes ago, Dialed In said:

Do you have a mechanical gauge or digital?

Mechanical

[gwav8or]

37 minutes ago, Dialed In said:

You can see the weep hole on my manifold pressure line at the top by a small dab of silicone if you zoom in. I think most are further down by the intake. 

Yep I see the weep hole on yours.  Mine doesn't have a weep hole that I can see and the MP line isn't the same as yours.  On mine, aft of the blue fitting (not sure what it's called) is a small rigid aluminum (I believe aluminum) hose/tube.  Like very small.  Probably 1/8" or smaller.  I added a pic of the one on mine to my original post.

[carusoam]

All of the mechanical MP gauges have a weep hole…

That lives in the 1/8” line about 1” from the gauge…

it is a calibrated hole with a tiny diameter…

All the vibration on an unsupported, soft, aluminum tube… causes cracks to form at the hole…

This all takes about 40 years to happen…

cut, the end off, drill new hole, reconnect…

The dimensions of the weep hole is in one drawing, but not all… in the instruments section of the maintenance manual…

I was looking in the M20C drawing, but was pointed to the M20F(?) drawing…. My second call to the Mooney factory in Y2K or so…. The engineer (Bill Wheat) was incredibly helpful.

Trying to measure the broken hole is a real challenge…

Accurate MP readings depends on the calibrated aspect of the weep hole…

Getting the drill bit… takes time to get shipped… unless you have a really good tool store nearby….

 

See how much an EI MP gauge costs for comparison… no weep hole required.  

 

PP thoughts only, not a mechanic…

Best regards,

-a-

[gwav8or]

All of the mechanical MP gauges have a weep hole…
That lives in the 1/8” line about 1” from the gauge…
it is a calibrated hole with a tiny diameter…
All the vibration on an unsupported, soft, aluminum tube… causes cracks to form at the hole…
This all takes about 40 years to happen…
cut, the end off, drill new hole, reconnect…
The dimensions of the weep hole is in one drawing, but not all… in the instruments section of the maintenance manual…
I was looking in the M20C drawing, but was pointed to the M20F(?) drawing…. My second call to the Mooney factory in Y2K or so…. The engineer (Bill Wheat) was incredibly helpful.
Trying to measure the broken hole is a real challenge…
Accurate MP readings depends on the calibrated aspect of the weep hole…
Getting the drill bit… takes time to get shipped… unless you have a really good tool store nearby….
 
See how much an EI MP gauge costs for comparison… no weep hole required.  
 
PP thoughts only, not a mechanic…
Best regards,
-a-

This is probably the way to go but….. Mine is the MP/FP combo so I’d probably be looking at the CGR-30P Premium. At a “premium” price too.


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[carusoam]

@gwav8or,

You just received the ‘need’ for a great upgrade…. 

we have the EI guy around here if you have questions…

Best regards,

-a-

[gwav8or]

1 hour ago, carusoam said:

@gwav8or,

You just received the ‘need’ for a great upgrade…. 

we have the EI guy around here if you have questions…

Best regards,

-a-

@carusoam Yes, this is very true.  I'll be taking the Mooney in the next week or two to have avionics installed.  I've committed to going the engine monitor route as the next upgrade.  I may consult with my CFO (wife) and see if we can squeeze a few more AMUs out of the budget.  :-)

I really love this plane and really honestly wish I'd joined the Mooney club/cult two airplanes ago.

[gwav8or]

BTW, problem solved.  Mechanic removed the MP tube (what is the correct term??) and found some debris.  Just got back from maintenance flight and all seems to be good now.

Thanks All!