Running on 3 Cylinders

Yesterday, after a week of grey weather, conditions finally made it possible to fly. I rolled out my RV-9, did all the checks and started the engine. My engine is a Lycoming O-320-D2J with a standard magneto ignition firing the bottom spark plugs and an electronic ignition firing upper sparks plugs.
After starting, the engine ran really bad and my Dynon showed no EGT/CHT increase on the number 2 cylinder, an indication of nill ignition in that particular cylinder.

Also, the Dynon failed to show RPM.

All of a sudden the cylinder started firing and the EGT/CHT's went above that of the three others, indicating only one spark plug firing.
After 30 seconds or so, that spark plug gave up again, leaving the engine running on 3 cylinders again... Dynon confirmed, the CHT/EGT on No.2 cylinder dropped.. Still no RPM on the Dynon

I repeated the whole thing minutes later and it happened again although it ran on all 4 most of the time. Dynon showed RPM again... (pfuhh..) I then did a run-up, increased RPM to 1700, leaned to burn deposits away and the engine ran just fine on 4 cylinders all the time....

Any idea what's going on here ? The bit I cannot comprehend is why there are moments that both spark plugs on a single cylinder don't seem to spark and why, without manipulating the controls, number 2 cylinder comes back online with only one spark plug firing...

Does the lack of RPM indications on the Dynon give a hint on what's happening ?

Does it make sense, after flying and before closing down, to increase power and lean the engine to burn deposits away and then close down in order not to foul the spark plugs ?

I'm no A&P and have very limited understanding on the inner life of a Lycoming but yesterday's experience doesn't increase my trust in this particular engine...

Loads of questions and I hope that I have been able to paint a clear picture. Your input is most welcome !

Possible Sticking Valve

Simon,

I recently helped with a similar problem on a friend's RV-4. What we found was an intermittent sticking exhaust valve.

Read the thread at:
http://www.vansairforce.com/community/showthread.php?t=63768

&, see the info at:

http://www.lycoming.com/support/tips-advice/key-reprints/pdfs/Key Operations.pdf

&

http://egaa.home.mindspring.com/valves.html

You might want to try a "poor man's compression check" to see if #2 is leaking compression - you'll need a helper with good hearing. Have your best ear(s) listening at the tail end of the exhaust pipe(s) while one of you turns the engine over slowly with the prop (check all mags & switches OFF while doing this check -- and do it on a cold engine). Good compressions and no leaks will be indicated by a BIG POOF at the exhaust pipe for each cylinder as it reaches it's height of compression and then it's exhaust valve opens. If you hear a hissing on a compression stroke, not followed by the BIG POOF, that cylinder most likely has a valve stuck (not seating) and it's compression is lost in the hiss. If #2 is the problem, this check will be easier if you remove one spark plug from each of the other cylinders.

Hope this helps.

Barney, in Memphis
RV-3 flying
RV-4 flying

The chances of BOTH ignitions failing on the same cylinder are very remote, this would lead me to believe you may have a sticking valve. "Morning Sickness" is the first indicator of a sticking valve.

I would do a cold compression test and have a look at all the plugs first, just pulling the prop through when cold can often identify the "dead" cylinder.

Lack of RPM on the Dynon does suggest an issue. My GRT gets its RPM input from the mag switch - actually from one of the P Leads from the mag. As a result when I do a mag check, on one side RPM goes to zero. So it suggests that your RPM comes from a P lead and when the RPM stops indicating, that that mag or electronic ignition that feeds the Dynon is being grounded.

Surely sounds like

a possible stuck exhaust valve...

You might want to try a "poor man's compression check" to see if #2 is leaking compression - you'll need a helper with good hearing. Have your best ear(s) listening at the tail end of the exhaust pipe(s) while one of you turns the engine over slowly with the prop (check all mags & switches OFF while doing this check -- and do it on a cold engine). Good compressions and no leaks will be indicated by a BIG POOF at the exhaust pipe for each cylinder as it reaches it's height of compression and then it's exhaust valve opens. If you hear a hissing on a compression stroke, not followed by the BIG POOF, that cylinder most likely has a valve stuck (not seating) and it's compression is lost in the hiss. If #2 is the problem, this check will be easier if you remove one spark plug from each of the other cylinders.

Click to expand...

When all of the above happened yesterday, I cancelled my flying plans (duhh...) and we moved the airplane into the maintenance hangar of our FBO since I'm about one hour short of a 50-hour inspection anyway. Drained all oil and since the engine was warm, did a proper compression check on all four cylinders. They were all well within limits so I'm sure that I don't have a compression problem.

I will start the inspection tomorrow and will seriously address the "morning sickness" issue. It sure sounds like my engine is suffering from it.

Love this forum and your immediate replies
Thanks a lot ! Keep you informed on what we find.

We took the cover off from the number 2 cylinder and took a serious look at the exhaust valve with the old rope trick. It moved absolutely wonderfully in its seat without any indication that it would or could stick. I have a strong impression that this cylinder is not suffering from a sticking exhaust valve.
We confirmed (by the way) by applying heat to the EGT-sensor that it was indeed the number 2 that occasionaly went offline last week. Spark plugs looked fine, we will address the ignition leads next.
Keep you all posted. If the are any suggestions, I would be glad to hear them

PH-SCP said:

We took the cover off from the number 2 cylinder and took a serious look at the exhaust valve with the old rope trick. It moved absolutely wonderfully in its seat without any indication that it would or could stick. I have a strong impression that this cylinder is not suffering from a sticking exhaust valve.
We confirmed (by the way) by applying heat to the EGT-sensor that it was indeed the number 2 that occasionaly went offline last week. Spark plugs looked fine, we will address the ignition leads next.
Keep you all posted. If the are any suggestions, I would be glad to hear them

Click to expand...

Finished the 50 hour inspection last week. As I mentioned, we took the cover of the no.2 cylinder and found the exhaust valve moving smoothly.

Cleaned all sparkplug contacts, removed the back cover from the magneto, inspected and cleaned contacts. Looked at the Lightspeed ingnition and was able to push the No.2 lead further into the receptor. In fact, it clicked twice, leading me to believe that there was a bad connection there.
It still doesn't explain why the other spark (from the magneto) wasn't firing.

Anyway, we ran the engine extensively after the inspection and flew it Saturday and it performed flawlessly..

It put the grin back on my face....
Thank you all for posting so many suggestions.

Same happened to me

Lost the number 2 cylinder on take off once - fortunately had enough runway in front of me to abort. For some reason BOTH spark plugs went south at the same time. Mechanic pulled them and verified that both plugs were bad. After plugs were replaced problem never happened again... weird.