M20J RPM Fluctuation

[KSMooniac]

I don't have any knowledge/experience with them, but I'd recommend you call Select and talk to Aaron about your symptoms.

[JCD]

KSMooniac - Who is Select?  Can you pass comms info?

 

-Thanks

JCD

[KSMooniac]

Here ya go:  http://selectaircraft.com/id6.htm

[Yetti]

Most have been mentioned.

1. Key switch could be grounding out

2. Check P leads

3. Check Fuel screens.  Gascolator and at the fuel servo

4. Do mechanical fuel pump check

5. bad spark plug harness

6. Magnetos

7. Fouled/bad plug

 

[Yetti]

And make sure your ignition key is one of one or two keys and not on a large ring with lots of other keys

[JCD]

22 hours ago, KSMooniac said:

2 hours ago, Yetti said:

And make sure your ignition key is one of one or two keys and not on a large ring with lots of other keys

 

Confused? How does this induce a problem?  Weight of keys on ignition switch?

[Andy95W]

I think he is implying that if your ignition switch is "iffy", then the weight of your keys could make your ignition switch short/ ground when it wasn't supposed to.

But again, if this were the case, then your problem would occur in all phases of flight, not just one specific phase, i.e., full power during the takeoff.

[JCD]

Ok...so after several weeks of trouble shooting we found the problem. Believe it or not it was air getting into the fuel system through a poor installation of the Gasalator smashing the O-ring. 

 

Thanks to Frank at Chandler Aviation!  He did a great jod deducting the problem and isolating variables until we found the root of the problem.  I have flown the plane several time and it flies like a dream. 

 

Thanks to all on Mooney Space for your thoughts and suggestions.

 

Justin

[BDPetersen]

Occam's Razor wins again.

[N201MKTurbo]

Ive had this happen before, but the engine fluctuations were always preceded by fluctuations in fuel pressure. Did you happen to see any fuel pressure changes?

[carusoam]

Reviewing the lists...

Yeti gets a point for mentioning the gascolater as a possibility.

FF indication was a little erratic during the problem.  FF sensors have a tendency to collect air bubbles and not report good data when this happens.

Congratulations on finding the problem.  Thanks for reporting the details here.

Best regards,

-a-

[JCD]

On January 3, 2016 at 8:35 AM, N201MKTurbo said:

Ive had this happen before, but the engine fluctuations were always preceded by fluctuations in fuel pressure. Did you happen to see any fuel pressure changes?

Funny you mention this. I have put about 15 hours on the plane since this and now my fuel pressure gage will, what seems to be randomly, start fluctuating and even redline during flight. Then drop back down after a while. I am starting to wonder if it's related.  The attached picture is a little hard to see with the glare but fuel pressure is reading high. No RPM fluctuations. Any thoughts?

 

[carusoam]

High fuel pressures are often associated with new fuel pumps...

Sloppy displays of instruments on the panel are often related to grounding continuity.  Whether the ground causes a high or a low reading depends on it's failure mode design.

other funky ground continuity issues are often caused by old and broken ground straps on the engine.  Or missing from the engine...

I am only a PP, not a mechanic.

Best regards,

-a-

[M20F]

On 1/3/2016 at 9:35 AM, N201MKTurbo said:

Ive had this happen before, but the engine fluctuations were always preceded by fluctuations in fuel pressure. Did you happen to see any fuel pressure changes?

Do you see this in a climb to high (teen's up) altitude?  I on occasion see this and have just ascribed it to vapor lock'ish issues which the boost pump corrects (I don't see RPM fluctuations though) and it cleans itself up after the pump runs a bit or I level off. 

[N201MKTurbo]

My problems were always related to a leaky fuel selector.

Have you tried switching tanks when you see the fluctuations? My problem was only on the left tank, when I switched it went away. Out of habit you usually climb on the same tank.

And yes, my problem appeared above 12000. 

[M20F]

16 minutes ago, N201MKTurbo said:

Have you tried switching tanks when you see the fluctuations? My problem was only on the left tank, when I switched it went away. Out of habit you usually climb on the same tank.

Yes doesn't do anything in my case.  Usually around 14000-17000 feet I will see fuel pressure slowly wind down towards 0, put the boost pump on, it leaps back up.  Turn boost pump off, it winds down again, put boost pump on it, it repeats.  I eventually figured out just turn the pump on it and leave it on and after 10-15 seconds it seems to correct and pressure stays solid the rest of the flight.  

[JCD]

On 12/3/2015 at 11:54 AM, KSMooniac said:

On 3/1/2016 at 10:06 PM, M20F said:

Do you see this in a climb to high (teen's up) altitude?  I on occasion see this and have just ascribed it to vapor lock'ish issues which the boost pump corrects (I don't see RPM fluctuations though) and it cleans itself up after the pump runs a bit or I level off. 

I don't have any knowledge/experience with them, but I'd recommend you call Select and talk to Aaron about your symptoms.

So just to be clear I no longer have any RPM fluctuations after the O-Ring on the Gasolator was repaired.  I have seen this High Fuel Pressure reading at higher altitudes.  I was at 11,500 when it went to red line (Boost pump off).  In the picture above I was on a 1200 Ft/Min decent from 11,500 to 3,500.  It wil go high and on its own after a while drop back down.

[N201MKTurbo]

32 minutes ago, JCD said:

So just to be clear I no longer have any RPM fluctuations after the O-Ring on the Gasolator was repaired.  I have seen this High Fuel Pressure reading at higher altitudes.  I was at 11,500 when it went to red line (Boost pump off).  In the picture above I was on a 1200 Ft/Min decent from 11,500 to 3,500.  It wil go high and on its own after a while drop back down.

I would look for an electrical issue in the gauges. My oil temperature does the same thing. I'm fairly certain it is in the round connector on the gauge cluster. The oil temp on my UBG16 is always rock solid, so I don't worry about it much...