Cylinder mystery

[Freight Dog]

I started my engine and it seemed to be running slightly rougher an normal, but noticed on my GEM that I had no indication of #4 EGT/CHT. Seemed a little odd.

Suspecting bad connection, I taxied to the run up area. I ran it up at 1900 rpm, but noticed the engine running a little rough. Mag check... 300 drop. Leaned it out, ran it for 15 seconds at 2000 rpm, brought it back, another mag check - 60 drop, but engine still not running quite right... I tried to run it to full power and it only gave me 2300 rpm. Still no data on GEM for #4.

OK, clearly we have a problem so I returned back to the ramp.

When we popped the cowling off, no obvious leak of any kind, we ran compression check, 78/80 on #4 cylinder. We pulled the bottom spark plug and it was slightly wet. Pulled the fuel injector, clean. Tested the fuel line by turning mixture rich, throttle open, fuel pump on, no issues. Scratching our heads... lets put it back together and try to run it. It purred... ran it up. 60 rpm drop on mag check. Ran it up to full power, like a homesick angel...

Strange...

Clearly the #4 cylinder wasn't firing as evident by slightly wet spark plug. That would also explain no EGT/CHT info on GEM.

Generally, I run it about 50-75 ROP (wanna go fast), though this weekend I played a bit by flying 50 LOP (nice tailwinds).

As a fairly new owner, any words of wisdom are greatly appreciated.

[carusoam]

A couple of things come to mind, it might be lost in the writing though...

(1) Were you able to measure Spark plug resistances while they were out?

(2) When you say no indication on EGT or CHT, it should be reading OAT unless you have a GEM issue as well? If only one plug is firing in a cylinder, expect strange readings compared to other cylinders, especially during run up.

Next identify Which magneto and or harness (l or r) is responsible. How old are the mags, wires and plugs?

Best regards,

-a-

[Freight Dog]

No we didn't. Just visually inspected them.

[thinwing]

After checking sparkplug resistance and plug wire continuity..its time to check magneto condition...check for arcing arround distributor towers...timing obviously...possible stuck valve that got freedup during comp check

[mcpilot]

Stuck valve? Morning sickness?  

[Freight Dog]

Had a few flights since.... engine purred.

 

I read about MMO and thinking about using it as a fuel/oil additive. Any of you guys doing it? 

[DS1980]

No MMO. Camguard only.