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My M20J Engine Fails on T/O - Can't figure out why

kaufmath

By kaufmath
in Modern Mooney Discussion

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kaufmath Newbie

kaufmath

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If you read no farther, here's the main takehome lesson:  use the whole runway...i almost didn't, and it saved my plane and my butt!  As it is, I walked away with no injury and no damage.  The question remains: why did it happen?


My '78 M20J engine 800 SMOH failed on takeoff about 1 month ago.  I'm still collecting opinions as to where the problem lies.  Maybe you can help?  It was a normal day in September, 75 degrees.  Normal pre-flight including sumping but not gascolating, normal start, normal taxi-out, normal run-up.  After normal lift-off at full power, at about 50 feet AGL, as I reached up for the gear handle, the power dropped to idle...basically nothing, though the engine did continue to run, just no power.  I set back down, scared but unharmed.  (always fly the airplane!)


So safely back on the ground, the engine will idle but ANY addition of power and it wants to quit altogether.  Every gage was in the green, no loss of fuel pressure. Of note, I did NOT have the boost pump on during the takeoff as I usually do that day.  Half tanks that day.  So I shut down, pull the cowl with local mechanic and find nothing on gross inspection.  Restart...same thing, it will idle but not take ANY power or it wants to die.  Boost pump has no effect.  Trying to lean on the ground does NOT lead to my typical normal slight increase in RPM.  After 5 minutes of sitting at idle wondering "what the heck", I change from left tank to right tank, and within 10 seconds problem goes away COMPLETELY.  She takes full power, runs fine, and re-switching tanks will NOT reproduce problem.  She had been on left tank from previous flight 1 week earlier, a flight which was turbulent, but otherwise uneventful.  So several runs up and down runway and ultimately 3 flights over airport, and it runs fine now.  Cannot reproduce the issue.  No debris in gascolator, no debris in throttle servo screen, no stuck valve, no problem in exhaust system found, and absolutely no water found after rechecking 10 times.  Not a drop. The only thing I notice is that if I try to lean out a bit at 3000 feet while circling the airport, the EGT (single cylinder only) temp does not come up nearly as high as previous...seems like a clue.  I haven't dared leave the pattern though.


If this way your plane, where would be the top 2 or 3 places you'd be looking now?  Any help is appreciated. 

N9937c Community Regular

N9937c

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I had an inflight failure almost same thing. turned out to be a bad hose on a fuel truck put rubber bits in the fuel, plane flew fine for 4 hours. next morning topped off, took off and 30 minutes later I am a glider. Would not restart until ~ 700 feet agl and would only make low idle power. Towed off runway and inspection started. Found Gaskolator coated in rubber bits. Faa found the hose the next day where i fueled for the 4 hour flight. All the sumping never revealed a bit of contamination.


larry

Cruiser Grand Master

Cruiser

Posted
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your descriptions sure sounds like some sort of restriction in the fuel supply. By changing tanks you dislodged or moved the restriction. Either in the selector on upstream from it.

Piloto Grand Master

Piloto

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Posted
Quote: Cruiser

your descriptions sure sounds like some sort of restriction in the fuel supply. By changing tanks you dislodged or moved the restriction. Either in the selector on upstream from it.

Piloto Grand Master

Piloto

Posted
Posted

Quote: Cruiser

your descriptions sure sounds like some sort of restriction in the fuel supply. By changing tanks you dislodged or moved the restriction. Either in the selector on upstream from it.

kaufmath Newbie

kaufmath

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thanks for all the advice.  fuel selector was locked on left tank.  no bits of anything in gascolator screen and never a drop in fuel pressure.  for fun, after it was running fine again, i moved the fuel selector to see how far towards OFF you could go before the engine would die.  half-way between left and off, fuel pressure drops and engine sputters.  i was no-where near that selection though the day of the event.  we have all the fuel hoses off for replacement, and the fuel servo AD mentioned above investigated and does not apply. 


is there such a thing as 'vapor lock'?  and if so, wouldn't the fuel pressure drop?  i'm debating sending the fuel servo in for inspection, though it was re-built 5 years ago.  cleaning fuel nozzles too.


 

rbridges Grand Master

rbridges

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when you had the problem, did the fuel pressure stay up when you tried to apply power?  You said it wouldn't do anything more than idle speed.  I agree with everyone else, it sounds like a fuel starvation issue.  I would think that you would have seen a drop in fuel pressure as you tried to increase power.

Shadrach Grand Master

Shadrach

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Quote: kaufmath

thanks for all the advice.  fuel selector was locked on left tank.  no bits of anything in gascolator screen and never a drop in fuel pressure.  for fun, after it was running fine again, i moved the fuel selector to see how far towards OFF you could go before the engine would die.  half-way between left and off, fuel pressure drops and engine sputters.  i was no-where near that selection though the day of the event.  we have all the fuel hoses off for replacement, and the fuel servo AD mentioned above investigated and does not apply. 

is there such a thing as 'vapor lock'?  and if so, wouldn't the fuel pressure drop?  i'm debating sending the fuel servo in for inspection, though it was re-built 5 years ago.  cleaning fuel nozzles too.

 

jetdriven Grand Master

jetdriven

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I would send the fuel servo off and tell them you had an inflight failure, and to look it over real good. Also check the flow divider and injectors.  I would probably postively verify the fuel tasnk vents are free, and disassemble the fuel selector valve.  This kinda problem gives me the willys.  i would definately dig deep, friend.

Clarence Enthusiast

Clarence

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You don't say the serial number of your aircraft but you have to eliminate fuel supply side of things first.. This should be easy and cheap to do, fuel vents as mentioned open and unobstructed, fuel pick ups (s/b M20-207) fuel selector valve, fuel gascolator, fuel boost pump, Dukes fuel pump out let filter ( AD 80-12-03 and S/B M20-222) This filter does not have a service requirement, most that I have seen have never been service since they were installed. Engine fuel hoses in the engine compartment checked or replaced.


After this it is into the engine compartment for more expensive parts, aside from the finger sreen in the servo there is little you can do other than remove it for testing/ repair, send the flow divider as well.


I had a similar issue on my first E model, a major power reduction on take off.  It was an internal failure in the servo, one of the stems on a diaphram was bent and sticking, likely caused by a backfire through the servo.


Good luck,


Clarence


 


 

kaufmath Newbie

kaufmath

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Thanks to everyone again for all the thoughts.  I'm making a list and will be checking everything twice.


We successfully changed all the fuel lines (based on Mooney Support suggestion) today and cleaned the injector tips and flushed the system by engagin the boost pump which the injectors off.  We caught the fuel as it came out in small cups, and there was some crud in each cup interestingly.  My mechanic thought not enough to cause a failure though.  I got brave and flew the aircraft after we worked on it (4th flight since failure all just above the airport).  She flew perfect.  Even the 'i cannot lean it to 650 anymore' issue went away now.  the first three flights it would not lean to EGT's above 500.  now it does, as it always did in the past.


can a fuel servo problem BE intermittent?  a friend at the airport suggested i contact the servo manufacture, which i thoght was a good idea too.  bad enough to cause a complete failure yet perfect the rest of the time?


i guess my understanding of the fuel selector is lacking, too.  taking it apart would probably help that.  so there is a difference between at the left tank position and clicking at the left tank position?  selecting Right is always easy.  selecting left in flight is always more challenging.


oh and yes, fuel pressure stayed fine when applying power...the engine just stumbled each time i pushed the throttle at all. 


i've accidently taken off without the boost pump before without any problems.  may have just been a coincidence as well.  hate to think too that had i had it on, i might have gotten 1/2 mile further and ended up in a field or on I-75.

jetdriven Grand Master

jetdriven

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The fuel servo on a Bendix RSA-5 uses ram air pressure into a tube (similar to a pitot tube) to give a reference pressure to a diaphragm, which in turn meters fuel to the divider and injectors. Anything wrong in this area can give you problems. I would have it recertified, IRAN'ed or whatever.

Piloto Grand Master

Piloto

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Kaufmath


Reading your initial reports and findings there is the possibility of debris slodge on the left tank fuel screen. As power is increased the debri will plug the inlet causing the engine to loose power. When you switched tank the debri may have fallen off away and that is why you can not replicate the problem. I would recommend to open the inboard panel of the fuel tank and check for debris in the fuel screen. If the tanks were resealed there is the possibility of sealant residue on the screen.


José


 

kaufmath Newbie

kaufmath

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i'm definately learning a lot about my airplane in this process!  gotta find the good in the bad.  and its amazing how wide the differential on this problem is...  I will take a look in the left tank, and painful as it is, I know the servo needs to go in.

jetdriven Grand Master

jetdriven

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These guys did my RSA-5 for the previous owners.  Give them a call, and maybe they can talk for a few minutes.   


 


Mike's Aircraft Fuel Metering


9406 East 46th Street North,


Tulsa, OK 74117-5807


(918) 838-6217 ‎

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