What's happened to my cylinder #2?

[maxmirot]

I did a run up a few weeks ago and found cylinder 2 with no EGT temp on one ignition.
I pulled the plugs a found oil had fouled the both plugs with more on the lower. The scope show normal valve but some glazing of the cylinder . Oil consumption was 1 per 10 hrs. I decided to change the cylinder with a new one. I did this with my mechanic.

I performed at 1 hrs test flight. I ran full throttle at 6000 feet about 80% hp. The #2 CHT was about same as the others at 350 degrees. The engine ran normally during the test flight.

I went to fly the next day. I did normal start and warm up with max ground leaning.
I did my run up and found cylinder 2 had a cold EGT again !
I have not pulled the plugs yet.

What do you think is happening? Next steps ?

Thanks
Max

 

[plehrke]

Look simple first. Check the EGT probe and probe wiring/connections. Maybe swap it to a different cylinder.

 

[lr172]

I did a run up a few weeks ago and found cylinder 2 with no EGT temp on one ignition.
I pulled the plugs a found oil had fouled the both plugs with more on the lower. The scope show normal valve but some glazing of the cylinder . Oil consumption was 1 per 10 hrs. I decided to change the cylinder with a new one. I did this with my mechanic.

I performed at 1 hrs test flight. I ran full throttle at 6000 feet about 80% hp. The #2 CHT was about same as the others at 350 degrees. The engine ran normally during the test flight.

I went to fly the next day. I did normal start and warm up with max ground leaning.
I did my run up and found cylinder 2 had a cold EGT again !
I have not pulled the plugs yet.

What do you think is happening? Next steps ?

Thanks
Max

Did you put new plugs in #2 or use the old ones? Need to isolate which plug is failing to fire (L or R ign). Then replace that sparkplug. Then get an ohmmeter on both ends of the plug wire. You are first checking the static resistance, then start moving the wire all around while observing the reading. This helps to find a failing wire that will present as intermittent. If this is a pmag, be sure the boot is fully pushed on and no issues with the terminal crimping one the coil side. These are crimped on by the installer and an area where many don't get it right. If a mag, you inspect the mags cap contact area (small copper disc that spring rests against) for issues as well as the spring to wire area in the harness cap. If it is a mag, may need to pull it apart to get the cap and rotor out. The #2 post could be worn down too far or there could be carbon tracking. You will need some guidance on reassembling the mag so don't do this on your own if you don't know the procedure.

Does it ALWAYS go cold on that one ignition or it is SOMETIMES? That will help identify more or less likely candidates.

Be aware that there could be an issue with the wiring of your switch and therefore will need more work to determine if LEFT is really LEFT. So if you don't find issues with one of the #2 circuits, check the #2 on the other side.

 

[lr172]

Look simple first. Check the EGT probe and probe wiring/connections. Maybe swap it to a different cylinder.

If it reads normal with two plugs firing and reads ambient with one plug firing, the chances of a probe issue over an ignition issues is VERY low. The symptoms all but confirm proper operation of the probe. If you can routinely make the EGT move with ignition changes and it NEVER moves without ignition changes, that pretty much confirms an ignition issue and not a probe issue.

 

[airguy]

I did a run up a few weeks ago and found cylinder 2 with no EGT temp on one ignition.
I pulled the plugs a found oil had fouled the both plugs with more on the lower. The scope show normal valve but some glazing of the cylinder . Oil consumption was 1 per 10 hrs. I decided to change the cylinder with a new one. I did this with my mechanic.

You elected to change a cylinder based on ONE incident of a lost spark plug? After just a runup?

wow...

 

[mahlon_r]

Does the engine get rough when the egt is NG? You don't mention roughness. If it isn't getting rough when the egt drops off, it isn't a problem with the cylinder or ignition, cause the engine is running normally. But instead indicates a problem with the indication. If it does get rough, then the problem is with the ignition to that cylinder.
Good Luck,
Mahlon

 

[maxmirot]

You elected to change a cylinder based on ONE incident of a lost spark plug? After just a runup?

wow...

I did want to get to long on the narrative. The cylinder looked partially glazed.

After looking at the cylinder and 2 oil fouled plugs , I opted for a new one

 

[maxmirot]

Does the engine get rough when the egt is NG? You don't mention roughness. If it isn't getting rough when the egt drops off, it isn't a problem with the cylinder or ignition, cause the engine is running normally. But instead indicates a problem with the indication. If it does get rough, then the problem is with the ignition to that cylinder.
Good Luck,
Mahlon

**** yes rough . not an indication.

The problem is now I did the new cylinder and still have the problem.

Yesterday I got no ignition on 2 for 45 to 50 seconds on a warm start

You can imagine the plane was shaking.

I have a new Dual Pmag system installed just before the new cylinder

 

[Mike S]

I have a new Dual Pmag system installed just before the new cylinder

Sounds like a good place to start your search.

 

[maxmirot]

This the lower plug before cylinder change. Pretty bad with oil fouling.
Looked bad enough to me to change the cylinder.

It is possible I jumped the gun on cylinder ?

 

[Mike S]

How many hours on the engine?

 

[maxmirot]

It has 650 hours

 

[bjdecker]

No surprise that changing the cylinder didn't solve the problem.

I would start by looking at ignition system here -- A failed plug, failed wire, failed MAG, Cap and any/all combinations thereof.

Also, I would google/VAF search for "Piston Ring Flush" or "Stuck Ring". This works, no foolin...

There's a third party device, whose name I cannot mention, that rides shotgun to the pMag stuff -- really good diagnostic info, should there be an issue with the pMags...