RobertGary1 Posted March 30, 2021 Report Share Posted March 30, 2021 On the ground my MP only goes down to about 14". If I reduce power below that the MP gauge rises. I put a hand pump and the MP line at the cylinder and verified I could hold 10" so the leak isnt in the MP line or gauge. In flight I can read 10" just fine. So I'm thinking the leak is somewhere that is low pressure in the cowl. Maybe the take tubes at the manifold? Thoughts? Also #3 always runs about 70F hotter than the rest so I'm thinking its there. Engine is 100 SFNEW, IO-360-A3B6 -Robert 1 Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted March 30, 2021 Report Share Posted March 30, 2021 Does your engine idle OK? Have you done a visual inspection? Awe all the intake tubes tight? Are the sump o-rings In place? Is the servo tight? Not a lot of places for it to leak that much. Could be the sniffle valve, but if you took it of the sump, it probably wouldn’t do that. Quote Link to comment Share on other sites More sharing options...
Ragsf15e Posted March 30, 2021 Report Share Posted March 30, 2021 I also don’t think #3 running hotter is necessarily a sign unless you’re at like half throttle or something less than wide open. At wide open, they should all be getting all the air they want, regardless of where it’s coming from. Hard to see an intake leak there. At idle, different story. Can you see a difference in the egts at idle? Also, #3 generally runs s bit hotter on lots of io-360s. 2 Quote Link to comment Share on other sites More sharing options...
RobertGary1 Posted March 30, 2021 Author Report Share Posted March 30, 2021 I don't see anything interesting on a visual. Idle seems fine although piston aircraft engines always stumble around a bit at idle but I don't think my Mooney is worse than the other piston planes I fly. Quote Link to comment Share on other sites More sharing options...
EricJ Posted March 30, 2021 Report Share Posted March 30, 2021 You can pressurize the intake with a shop vac or similar and spray soapless (or otherwise) bubble mix around to find a leak. 2 Quote Link to comment Share on other sites More sharing options...
RobertGary1 Posted March 30, 2021 Author Report Share Posted March 30, 2021 48 minutes ago, EricJ said: You can pressurize the intake with a shop vac or similar and spray soapless (or otherwise) bubble mix around to find a leak. I have a commercial automotive smoker so I thought about using that. But if it only happens under heavy vacuum it may be hard to recreate. Quote Link to comment Share on other sites More sharing options...
EricJ Posted March 30, 2021 Report Share Posted March 30, 2021 1 minute ago, RobertGary1 said: I have a commercial automotive smoker so I thought about using that. But if it only happens under heavy vacuum it may be hard to recreate. The smokers can leave an oil film on things, so I've avoided using them on the airplane. The fuel servo seems to sometimes be picky about ingesting some things in the ram tubes, so I'm a little paranoid about that. I use them for automotive leak checking, though. 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted March 31, 2021 Report Share Posted March 31, 2021 If we are discussing the mechanical MP gauge... It sounds like the calibrated weep hole has become uncalibrated... If the engine is working pretty well... and the MP gauge is always reading higher than usual... The weep hole is allowing more air into the MP line than expected... the weep hole is about 1” behind the mechanical MP gauge... If you have a JPI, the small amount of air entering the closest cylinder may register a higher EGT... making an outlier in your GAMI spread... This issue comes up about once a year... the hole has a tendency to crack and propagate... PP thoughts only... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
kmyfm20s Posted March 31, 2021 Report Share Posted March 31, 2021 I had that happen to me. On approach and on the ground couldn’t get MP below 13” but the plane ran as it should. Turned out to be a crack in the line going to the MP gauge sensor. 2 Quote Link to comment Share on other sites More sharing options...
RobertGary1 Posted March 31, 2021 Author Report Share Posted March 31, 2021 4 hours ago, kmyfm20s said: I had that happen to me. On approach and on the ground couldn’t get MP below 13” but the plane ran as it should. Turned out to be a crack in the line going to the MP gauge sensor. But like I said using a hand pump at the line where it goes into the manifold I can suck it down to 10” and hold it forever. Quote Link to comment Share on other sites More sharing options...
RobertGary1 Posted March 31, 2021 Author Report Share Posted March 31, 2021 7 hours ago, carusoam said: If we are discussing the mechanical MP gauge... It sounds like the calibrated weep hole has become uncalibrated... If the engine is working pretty well... and the MP gauge is always reading higher than usual... The weep hole is allowing more air into the MP line than expected... the weep hole is about 1” behind the mechanical MP gauge... If you have a JPI, the small amount of air entering the closest cylinder may register a higher EGT... making an outlier in your GAMI spread... This issue comes up about once a year... the hole has a tendency to crack and propagate... PP thoughts only... Best regards, -a- Idk that doesn’t sound like what’s happening here. Quote Link to comment Share on other sites More sharing options...
carusoam Posted April 1, 2021 Report Share Posted April 1, 2021 On 3/30/2021 at 11:32 AM, RobertGary1 said: 1) On the ground my MP only goes down to about 14". (Behavior of a leak) 2) If I reduce power below that the MP gauge rises. (Behavior of a crazed instrument) 3) I put a hand pump and the MP line at the cylinder and verified I could hold 10" so the leak isnt in the MP line or gauge. In flight I can read 10" just fine. (Great test) 4) So I'm thinking the leak is somewhere that is low pressure in the cowl. Maybe the take tubes at the manifold? Thoughts? Also #3 always runs about 70F hotter than the rest so I'm thinking its there. Engine is 100 SFNEW, IO-360-A3B6 -Robert Robert, I parsed things out a bit... didn’t change any words... Added numbers to the issues covered... (and observations / ideas in parentheses) Sounds like T-ing in another MP instrument may be a good idea... Because I can’t figure out how such a simple system can do #2... It is either a crazed gauge... or something further upstream misbehaving... The M20C would have a chance of LL getting stuck at that end of the MP line... the carb and evaporation leaves a lot blue glue in the area... Its possible something similar is happening with your MP line/intake as well... just not nearly as much blue goo on average... Or is somebody trying to sell you a new EI MP gauge? This is an interesting puzzle... maybe @M20Doc would be interested in a review of what you have... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Steve2 Posted April 1, 2021 Report Share Posted April 1, 2021 Excessively rich idle mixture will cause high idle MP indications. Try idling at 800-1000rpm and slowly lean the mixture to ICO; if it's too rich you'll see several hundred rpm increase along with decrease in MP. Quote Link to comment Share on other sites More sharing options...
Chocks Posted April 1, 2021 Report Share Posted April 1, 2021 Is there any aversion to doing some quick spritzs of carb cleaner at the potential intake leak spots to verify during idle? 1 Quote Link to comment Share on other sites More sharing options...
EricJ Posted April 1, 2021 Report Share Posted April 1, 2021 7 hours ago, "Chocks" said: Is there any aversion to doing some quick spritzs of carb cleaner at the potential intake leak spots to verify during idle? Propane works, too, but it's a little tricky on an airplane due to the big fan. Quote Link to comment Share on other sites More sharing options...
RobertGary1 Posted April 1, 2021 Author Report Share Posted April 1, 2021 1 hour ago, EricJ said: Propane works, too, but it's a little tricky on an airplane due to the big fan. That's why I wonder wondering about a smoker. That is what's used in cars. Its just warmed up mineral oil. Can that really damage anything? Quote Link to comment Share on other sites More sharing options...
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