Troubleshooting Issue on M20J, running rough and low EGT/CHT on one cylinder.

[lukejb]

So I flew my Mooney today for the first time since it came out of annual and had a few strange issues. Flew up to KGLE (Gainesville, TX) to top off the tanks with fuel, only about a 30 mile trip from my airport. Flying up there everything seemed fine and worked like I would expect it to. However on flight back shortly after takeoff engine started running a little rough sporadically. I never had a large loss in power i would say if any drop it was less than 100rpm, but you could tell it was cutting out or missing. The glare-shield would vibrate a lot when it did. It would only run rough for about 2 to 3 seconds at a time and then clear up and be fine for 20 or 30 seconds and then do it again. The other odd thing was the #3 cylinder on my insight engine monitor was reading really low and sometimes it was even not showing any temp Reading at all. Number 3 would occasionally bounce up to the normal range with all of the other cylinders but for most of the trip it was very low. Fuel pressure looked good. I checked both mags in flight and they both seemed good, very slight drop in power but prob less than 25rpm each. The cutting out/rough running of engine appeared to happen more when I would adjust manifold pressure, as I got within about 8 miles of my airport I began to inch mp pressure back. As I did this I noticed less cutting out/rough running of engine and the number 3 cylinder on insight monitor read a more average reading that was in line with the other cylinder CHT and EGT readings.

My first thought was water in fuel or ignition. After landing I opened the cowl to see if all plug wires were connected well and they appeared to be. Nothing obvious that I could see wrong with the cowl off. From the way it was running i thought there might be some arcing so i looked at spark plug wires but they looked good and are really not that old. Pulled spark plugs on number 3 as well. They looked good.... I sumped tanks for water and there was not any.

The dual mag was pulled off and overhauled this annual. It was running perfectly before the annual but since the dual mag had 514 hours on it we decided it was time to overhaul it at this annual.

Also all compressions at annual were 76/80 and above.

Any ideas?

[KSMooniac]

What kind of spark plugs are you using, and were they measured for resistance at annual?

[lukejb]

Not sure, I think they are champions but not sure which model. Not sure if they were measured for resistance. How is that done?

Mechanic is meeting me at the airport in the morning to test it out with me. We are going to run it up and if everything checks out on it will fly it. I was telling him about it all and he was not sure what it could be.

[kortopates]

Looking like a plug is cutting out. Using your engine monitor, do your magneto/ignition test and it should point to the problem spark plug. If it is normal on the ground, do the same ignition stress test in the air while preferably LOP to stress it more and you should see which plug is failing by a lack of an EGT rise while on one mag.

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[KSMooniac]

Champion has been building some poor quality plugs for many years now.  The simplest test is to use a multimeter and measure the resistance between ends of the electrode (one probe on the cylinder end, and the other inside the plug where the spring contacts the center).  It should be 5000 Ohms or less.  With Champion, you might find them XXX,XXX Ohms or even infinite/open.  Replace with Tempests.  I started having failures with my last set of Champions in under 100 hours.

 

Paul's recommendation for a LOP mag check in flight is good too.  It is the best stress test for an ignition system.  You might be unlucky enough to have two failing plugs on the same cylinders.  I'm not sure if the Insight monitor will have enough resolution to really detect small differences.  Does it have download capability?

[lukejb]

Yeah it does have download capability but I really have no idea how that is done. It is one of the early models, Insight GEM I believe. I think the plugs have around 250-300 hours on them so it may well be time for a new set. What model Tempest do you use in your Mooney Scott?

[DonMuncy]

You might check your number 3 fuel injector for some blockage.

[lukejb]

Good point Don. I was thinking that might be something we need to look into.

[DonMuncy]

If it were mine, I would pull that injector first and if I found something, I would blow it out and test fly it. If I didn't find anything, I would run some fuel through the injector, button it back up and fly it carefully in the pattern to see if the problem disappears. If the problem persisted, I would go to the spark plugs etc.

[KSMooniac]

The injector could be a problem as well, but I would think if it were blocked it would've stayed blocked and not come back on line.  There could be some intermittent fuel issue upstream from the injector, though.  Those are tough!  A partial blockage of an injector would cause the EGT to rise as the mixture gets leaner (less fuel) if flying ROP, or it would cause it to go down if flying LOP.  Completely blocked = no EGT.  

 

I'm now running Tempest fine wire plugs, but don't remember the model # off the top of my head.  Either those or the Tempest massives would be a fine choice.  

 

I have no experience with Insight monitors, so I can't offer advice there.  You might figure out what the resolution of the display is, and if it can be put in a finer or normalized mode like the JPI.  That way you can see small changes in EGT and really detect problems.

[lukejb]

I was running it ROP. Thanks for the advice! We will see what we can figure out tomorrow...

[marky_24]

Not to scare you but that's the exact symptoms my 201 had right before the #3 exhaust valve seat dropped out of the head. It put enough metal particles in the oil that we would have had to do a teardown to clean it all up, so we did a rebuild. $32000 later we were flying again. Bust out a borescope and check the valve and valve seat really good before you go back up.

[romair]

Unless the injector was completely clogged, you'd actually see a higher EGT if you have a partially clogged injector when running rich of peak.

[lukejb]

Mark, your egt and cht were low or not even registering temps on your number 3 as well?

[M016576]

Best case scenario: partially plugged injector.

Worst case scenario: exhaust valve going bad.

Clean the injector on #3 and bore scope the cylinder while the cowl is off- shouldn't take more than an hour or so. That's what I'd do.

I had two injectors get clogged on my M20J, and one in my missile... Egt dropped to ~800 on one clog, 0 on one (total stoppage), and rose 75 degrees on another... Cht to low 200's on the first 2, but rose 20 degrees on the third. It all depends on how much fuel is getting into the cylinder.. Clogs can vary from minor to complete stoppage of flow, so EGT/CHT can vary.

[lukejb]

Compressions were all in high 70's last week when mechanic checked them. If exhaust valve was going bad wouldn't there be lower compressions on that cylinder?

[marky_24]

In my case the plane had just had a prebuy done on it, all cylinders 74 and above. Fast forward 14 hours later and I was getting a lose of power on take off roll. I aborted the take off and went back to the runup area and did a mag check, it all checked out. Take off #2 same thing, this time I did a high rpm lean run up thinking there was a piece of lead causing my issues. Finally #3 everything was fine off we went. I was doing my check out with a CFI, flight went great until on the way back, 3 miles out I get the lose of power when I pull the throttle back. Just long enough to make my heart skip a beat. Didnt do it again until on down wind. Looked over and #3 was low cht and no egt, again it goes away. We land and taxi to the hangar and shut down. He signs me off blah blah blah, I hop in the plane to go fuel it. I had the hardest time starting the thing, and when it did fire and was rough as all hell, #3 no cht, no egt. Shut it down and pulled the cowl and #3 top plug hoping it was just a fouled plug..... nope little aluminum shavings everywhere, called the mechanic over and stuck the borescope in and saw the valve seat had fallen down and was blocking the exhaust valve open.

[M016576]

Compressions were all in high 70's last week when mechanic checked them. If exhaust valve was going bad wouldn't there be lower compressions on that cylinder?

I would expect that- but if the problem is intermittant, it could be a warped valve that is seating ok most of the time, but as the valve rotates, it finds the "bad spot" and sticks closed (or open... Or doesn't seat).

No harm in looking while you clean the injector- just to cover your bases. It also gives you a chance to check your plugs- make sure your spark plugs in that cylinder aren't backing out... If one wasn't properly torqued, that could be the problem, too, however unlikely. You can get all this done in about an hour. Although if you have a shop do it for you, they will probably charge you for 2 hrs.

[FloridaMan]

You might check your number 3 fuel injector for some blockage.

 

Yup. I had the exact same issue; ended up being a little flake of something in my #3 injector. Also, when running up on the ground at lower power setting -- say, around 1900 RPM, that cylinder was way hotter than the others. As I added power, the EGT dropped to nothing. 

[carusoam]

Reviewing the options....

(1) spark... Plugs, wires,

(2) fuel... Plugged or partially plugged injector

(3) air...

(4) ability to breath... Valve challenge

(5) cylinder #3 only

(6) The Annual inspection process removes the plugs for cleaning and inspection.

(7) a dead plug would show during run-up, in flight it may show higher EGT

Did I get it all?

-a-

[BigTex]

#3 is where your MP line connect too. If that line has a leak or isn't connected securely you'll seen those symptoms.

[lukejb]

Flew Mooney again this morning. Had mechanic go up with me. Of course it ran perfectly with him in it ha. Engine had no hesitation this time. Ran smooth entire time. EGT on Number three was slightly low and bounced around a lot. Would jump up 150 degrees then a second later back down 150 degrees. With such rapid change in temps on it, it led us to believe it may be a bad probe. Current probes have over 1,000 hours so probably time for a whole new set. Compression on number three still really good. I Think I'll keep flying it and change out Champion plugs to a new set of Tempest and order new egt and cht probes.

[KSMooniac]

I'm 95% sure that is a failing plug, not a probe failure.  Change your plugs first, and then see what happens.  This is the beauty of an engine monitor reducing diagnostic time (without a LOP/ROP debate!).  

[N601RX]

The 150 increase in egt is pointing to one of the plugs not firing.  Turn one of your mags off in flight and you will see the same increase or more if you leave it off very long.  EGT probes will eventually burn up due to the environment they are in, but CHT probes should not go bad as long as the wires to them don't break or rub.

[lukejb]

Good to know. Also one other thing I forgot to mention. During run-up this morning had a 300 rough drop on left mag. Increased power to 2200 rpm and leaned aggressively and then checked left mag again and it was fine. I always lean for taxi. So I guess that would also indicate spark plug going bad.. Guess I can't really say engine ran great bc of that but after takeoff and in flight everything was good. Plugs have well over 300 hours on them so I think it's due.