M20J Strange engine behavior - question to the forum

[mulro767]

I'm noticing several lights that grab my attention. Gear down, and low volts flashing. Also you mention 2500 rpm? So how steep of an approach are we talking about here? I've never heard of anyone operating a Mooney in a descent like that. Nor have I seen this problem before.

I would suggest a flatter descent and, like Bob said, a different power setting like 20"/2200. You'll cool the engine down slowly and still hold a good groundspeed and descent rate.

[jetdriven]

If the airspeed is greater than ~110-120 knots, at 15"of MP the airplane is probably pushing the prop.  Later in the video the MP is even lower.  You can feel this threshold when the engine goes to negative torque, its a very slight shudder. That may aggravate a sticking valve because the cylinders start to cool quickly.

 

Try using 18" MP as a descent limit, to slow down just level off for a mile and let the speed bleed off, then lower the power to descend and land.   You might try and put a quart of MMO in there and see if it goes away.

 

I'd definately bore scope the cylinder and look at the valves. Also, download your EGT trace during cruise and look for the telltale signs of a burned valve, a small rise in EGT for a few seconds about once every two minutes, it will be at a repeating time interval as the burned part of the valve rotates over the burned part of the seat. The GT rise is the escaping exhaust gas.

 

It may be spark plugs fouling, Ieaning to peak EGT during descent may help that issue.

 

When did you get to fly the space shuttle sim? I got to fly it once. Really cool.

[mooniac15u]

The change in manifold pressure and the engine vibration do not necessarily mean that the sensor is not malfunctioning.  The correlation could be spurious or could be related but not in a meaningful way (e.g. whatever is happening with your MP is inducing the sensor malfunction).  In a laboratory setting if we encounter anomolous readings from an instrument the first step is to recalibrate the instrument and repeat the experiment before drawing any conclusions about the data.

[PaulB]

The change in manifold pressure and the engine vibration do not necessarily mean that the sensor is not malfunctioning.  The correlation could be spurious or could be related but not in a meaningful way (e.g. whatever is happening with your MP is inducing the sensor malfunction).  In a laboratory setting if we encounter anomolous readings from an instrument the first step is to recalibrate the instrument and repeat the experiment before drawing any conclusions about the data.

That makes sense to me.  Especially since the vibration starts a little before the change in EGT temp.  Could be vibration induced probe or wiring malfunction.  If it's shaking a lot maybe thats why it keeps going up and down as the circuit gets interupted and is restored rapidly

[jetdriven]

The vibration is likely the cylinder going offline, but it's a small vibration because the engine isn't producing any power.

[ArtVandelay]

The vibration is likely the cylinder going offline, but it's a small vibration because the engine isn't producing any power.

Can't you test this theory by simply goosing the throttle and see if the vibration gets worst?  If the vibration goes away then it could be negative torque you discussed above?

[carusoam]

You have an electronic indicator that says something isn't right.

You have a vibration sensor (buttock?) that gives a matching indication.

When it happens is predictable.

I've had the experience of a stuck exhaust valve. Stuck closed, bent the valve and robbed the plane of more than 25% of it's four cylinder's power. I didn't have a fancy monitor, so I don't know what it would look like. Mine occurred on departure where 100% power was expected.

That is a very uncomfortable situation.

If it were only the electronic gauge, the EGT is expected to fail on it's own. There is no vibration associated with that.

Fortunately you know what cylinder it is.

What is the cost of the valve rope trick? Pull the valve, clean the guide, and measure the shaft for any bends.

It is unusual to have an EGT go out. It is really unusual to have an EGT go out with an associated vibration.

Best regards,

-a-

[jetdriven]

Can't you test this theory by simply goosing the throttle and see if the vibration gets worst?  If the vibration goes away then it could be negative torque you discussed above?

The vibration from negative torque is very subtle but it's there, probably caused by disturbed air over the tail, or from air passing through the prop and rolling off the front trailing edge. The vibration from a misfiring cylinder is noticed in climb and cruise becuase of the high power setting and the high demand on the cylinder which is now not doing its share. But at 15" in a descent, that's pretty close to zero torque and probably negative. So a dead cylinder will be masked. Pull the throttle to idle sometime and descend in a glide. Then pull the mixture. No discernible change. MP and RPM all respond normally.

Next time the EGT does this, quickly goose the throttle to 23" and see if it shakes. If it does, it's a dead cylinder.

[Piloto]

You have an electronic indicator that says something isn't right.

You have a vibration sensor (buttock?) that gives a matching indication.

When it happens is predictable.

I've had the experience of a stuck exhaust valve. Stuck closed, bent the valve and robbed the plane of more than 25% of it's four cylinder's power. I didn't have a fancy monitor, so I don't know what it would look like. Mine occurred on departure where 100% power was expected.

That is a very uncomfortable situation.

If it were only the electronic gauge, the EGT is expected to fail on it's own. There is no vibration associated with that.

Fortunately you know what cylinder it is.

What is the cost of the valve rope trick? Pull the valve, clean the guide, and measure the shaft for any bends.

It is unusual to have an EGT go out. It is really unusual to have an EGT go out with an associated vibration.

Best regards,

-a-

 

Is not the probe that is failing but the connection to it. The wire connection could easily be affected by engine vibration or engine cooling air flow. The cowl flaps setting could affect the airflow thus the EGT connection, because the wires may be fluttering. Trey before doing anything to the engine check the EGT connection. I had this same problem with the EGT and CHT probes and was always a connection problem. BTW if it was an engine problem with that EGT drop the vibration would have not have been subtle but a shaky one.

 

Jose .

[carusoam]

I get it, vibration causing a probe/wiring issue.

Can a real EGT actually flip flop from 1200-1600dF?

I think that's what I was seeing...

It would be really helpful to have the actual data file...

If the valve is not closing...fuel is burning on the way past the valve, indicating higher EGT.

If that's a real temperature, it is really hot on things that are not used to getting that hot...

This is purely speculation on my part. Ignore it if it is not helpful...

Best regards,

-a-

[treyizy]

Thanks everyone for the great suggestions. I'll be sharing the lot with my mechanics and get back with the results.

 

I'll be flying today and try several of the descent profile changes to see how it goes. 

[treyizy]

If the airspeed is greater than ~110-120 knots, at 15"of MP the airplane is probably pushing the prop.  Later in the video the MP is even lower.  You can feel this threshold when the engine goes to negative torque, its a very slight shudder. That may aggravate a sticking valve because the cylinders start to cool quickly.

 

Try using 18" MP as a descent limit, to slow down just level off for a mile and let the speed bleed off, then lower the power to descend and land.   You might try and put a quart of MMO in there and see if it goes away.

 

I'd definately bore scope the cylinder and look at the valves. Also, download your EGT trace during cruise and look for the telltale signs of a burned valve, a small rise in EGT for a few seconds about once every two minutes, it will be at a repeating time interval as the burned part of the valve rotates over the burned part of the seat. The GT rise is the escaping exhaust gas.

 

It may be spark plugs fouling, Ieaning to peak EGT during descent may help that issue.

 

When did you get to fly the space shuttle sim? I got to fly it once. Really cool.

I flew the shuttle sim at the shuttle avionics integration lab just before the final shuttle flight when they had extra time in the sim as the astronauts were past their prep phase and the sim was scheduled to be shut down the following month.  We did a RTLS abort after loosing the left main engine, flying to 330,000 ft. at Mach 6. Doing a powered pitch over and returning to land at Kennedy Space Center.  It was truly amazing!   ...though my landing was a little hard and I apparently collapsed the gear

[rhallmark201]

I would put 1/4 a bottle of Marvel Mystery oil in each tank.. if your having stuck valve issue this will clear that up (at Least it did in my experience). BUT I had this same issue on

a Cessna 310 and it came to be a defective spark plug wire that was breaking down after a 2 hour trip..  Do you do a Mag check in the air?

[Jsavage3]

Take a look at the MAPA Mooney Manual page 3-14...final paragraph under Descent Performance.  High RPM with low MP is not were I want to be during the decsent.  I'd recommend that you start your descent by reducing RPM rather than MP.  My MP stays up until I'm pulling the power to get the gear down -- this helps keep my temps up and minimizes piston ring flutter.  Even then, my MP stays at or above 20" until I begin my descent from pattern altitude.

 

I suspect you've got a sticky valve situation developing in #1.  See topic here titled, "Sticky Valve_Lycoming IO-360-A3B6D" and I believe you'll see some similarities as well as the fix that corrected my sticky valve issues.

 

Good luck and keep us posted!

[Alan Fox]

Before you you try crazy stuff start with the basics..... Pull and regap the plugs , and check for a cracked insulator....rotate the plugs between cylinders....also , if you can duplicate the problem , do a mag check to see if you lose a cyl totally , could be harness if this happens......Lower power settings need more energy for the spark to jump the air gap , as the richer fuel mixture works to help "conduct" the spark........Remember BASICS ........ It usually is something very simple....

[bnicolette]

Have the #1 exhaust valve reamed.  It is less than a 2 hour job if that.  Manifold pressure up and EGT down is definitely screaming sticky valve.  Same symptoms of morning sickness.

 

See picture attached.  

[jetdriven]

That graph is likely offscale on the EGT note the flat line at the top before it comes down.

[bnicolette]

That graph is likely offscale on the EGT note the flat line at the top before it comes down.

 

Byron these are some more pics.  Note that I am zoomed in VERY far (definitely not off scale)  I've included a picture without zooming in.  Generally this was happening to me within the first 3 minutes of start up.  Once I had the valve reamed out........no more issues.  I've included a picture on the flight before the valve was reamed and then another one after the valve was reamed.

[FlyWalt]

Take a look at the MAPA Mooney Manual page 3-14...final paragraph under Descent Performance.  High RPM with low MP is not were I want to be during the decsent.  I'd recommend that you start your descent by reducing RPM rather than MP.  My MP stays up until I'm pulling the power to get the gear down -- this helps keep my temps up and minimizes piston ring flutter.  Even then, my MP stays at or above 20" until I begin my descent from pattern altitude.

 

I suspect you've got a sticky valve situation developing in #1.  See topic here titled, "Sticky Valve_Lycoming IO-360-A3B6D" and I believe you'll see some similarities as well as the fix that corrected my sticky valve issues.

 

Good luck and keep us posted!

 

 

One thing that I appreciate in this forum is how much I am still learning after two years of Mooney ownership :-)

[pinerunner]

One thing that I appreciate in this forum is how much I am still learning after two years of Mooney ownership :-)

That advice seems to agree with John Deakins.

[Royski]

I wonder if it might be a slightly loose intake pipe