Electronic Ignition System - rough running engine

[Stinson Matt]

Folks, any guidance or steer would be appreciated.

Faultless first flight of the day. Upon engine check pre-departure of the return flight, the engine ran excessively rough on 'L' only and on the emergency battery check. I assumed fowled plug as she ran normally on 'Both' and elected to depart. Shortly after takeoff I could feel the engine running a little rough, no warning indicators shown but decided to make a precautionary landing back to the strip. Upon engine run check, same issue.

I removed all plugs, no evidence of any fouling. I made sure all the ignition system plugs were tightly in place, nothing appeared loose nor out of place. Refitted all the cowlings and no recurrence of the previous issue. Flew back to base with no issues.

Any thoughts friends?

Thanks in advance.

Matt

[Andy]

engine ran excessively rough on 'L' only and on the emergency battery check.

Emergency ignition battery normally powers Right system only and is tested with key switch in Right Only position. (Left off, test Right with normal and then emergency power)

Can you confirm that you had rough running on Left only and R only (emergency). Also that engine was smooth on Both and Right only (not emergency).

Andy

[Daveembry]

Your best diagnostic tool for those types of situations is your egt’s. Every run up I do is with the engine page up so I can watch all 4 cylinder egt’s on run up. Watch them when you switch from L to R. If you have a problem with a coil, or coil lead, fouled plug, etc. it will show immediately on the affected cylinder. Then you can see which cylinder is having the problem and check it out. The left ignition box is all top cylinders and the right is all the bottom cylinders. So if you see egt’s drop on L #3, you know it’s the top #3 with the problem.

A common problem area is where the ignition lead wires connect to the coils. The wires are extremely thin and have a tendency to break where they attach to the spade connector. If it’s partially broken, it could occur intermittent. I’ve had one break before (affected just 1 of the plugs kn a cylinder) and just flown home because the ignition boxes on both will compensate and you hardly notice it other than egt averages being different on that cylinder.

In your case, perhaps it’s one of those ignition wires either broken or a few strands broken and intermittent?

Also, there is a Service Letter from CC that tells you to inspect and correct those connections (ignition wire to the spade connector that attaches to the coil). You can do a search here and get that and see what I’m talking about.

I actually keep this photo of the wire routing in my Favorites on my phone in case I’m away from base and need to track it down (since getting old seems to have shortened my memory 🤦*♂️)

964F95EB-CD59-4CC2-929A-0F4D7CE805D4.jpg

Folks, any guidance or steer would be appreciated.

Faultless first flight of the day. Upon engine check pre-departure of the return flight, the engine ran excessively rough on 'L' only and on the emergency battery check. I assumed fowled plug as she ran normally on 'Both' and elected to depart. Shortly after takeoff I could feel the engine running a little rough, no warning indicators shown but decided to make a precautionary landing back to the strip. Upon engine run check, same issue.

I removed all plugs, no evidence of any fouling. I made sure all the ignition system plugs were tightly in place, nothing appeared loose nor out of place. Refitted all the cowlings and no recurrence of the previous issue. Flew back to base with no issues.

Any thoughts friends?

Thanks in advance.

Matt