High EGT on #4 cylinder fixed ?

[nels]

Since I've been flying my M20E, only about nine hours now, I have noticed that the number four cyl EGT is always higher than the rest. A couple weeks ago during a mag check we noticed a large drop in rpm and abnormally high EGT on cyl four so aborted the flight for the day. Several days later a pulled the bottom plug which was the problem plug according to the monitor. It was wet and had plenty of carbon build up down inside so I sand blasted it clean and reinstalled it. I started the engine and it ran well through a mag check. While it was idling I leaned until engine rpm drop then enrichened. EGT on four was again high. I applied power and the engine began to backfire so I enriched the mixture to full rich and had the same backfiring. Engine was running rough when I did another mag check which showed no difference in rpm. I glanced at the #4 cyl temp again and saw it had gone to zero. Disgusted, I shut it down. The following day I pulled the prop through about a dozen times to make sure I didn't lose a cylinder or stick a valve; fortunately all four still had great compression. I thought I probably had a dirty injector on four so I pulled the injector out of four and number one. With the injectors connected to the feed lines I put each into a small prescription bottle and set the mixture to full rich and turned the electric pump on for 30 seconds. I expected to see a volume difference between the two but they were precisely the same. While replacing the injectors I just happened to notice that the flare connection interface on number 4 had a carbon layer approx 1/3 to 1/2 the circumference of the sealing surface. The deposit was easy to flake off with a dental tool. I'm sure this had been leaking for some time. Not sure why it wasn't sealing up as the fitting was tight. I assume there was a small speck of debris at the interface which prevented the seal? Anyway, I pulled the top spark plug, it was carboned up down between the porcelain and wall so I cleaned it out with a dental pick, gun cleaning fluid and compressed air. I then removed the previously cleaned bottom plug and used the gun cleaner and compressed air on it. I recowled the engine. I then started the engine, let it warm, leaned to eng rpm drop and enrichened. For the first time since I've owned this plane all the exhaust temp were about the same. I ran it at various rpm's, rich, lean, etc. and the exhaust temperatures all remained about even to each other. All this time I thought I had a bad instrument or I just didn't know how to operate it correctly.

I hope I didn't bore anyone with all my windage but I thought someone else out there may benefit from this. I will also say that the engine has never run so smooth and able to idle so gracefully at 700 or 800 RPMs since I started flying it. Once I'm able to get back in the air I will know for sure I've remedied my problem but for now I feel pretty confident. Should I be?

[HRM]

Windage? Hardly!

 

I have had a very similar problem with #2 and have tried everything except for what you did.

 

When I bought my plane four years ago it ran like a top. Now, time has past as well as three annuals and #2 is driving me crazy. I am betting this is where it is going.

 

Thanks very much for the tip, I'll let you know how it goes.

[Andy95W]

Nels, thanks for the detailed post. I own a C model but as an A&P I work on a good number of fuel injected engines.

I think you should be very confident in your work. As diligent as your work sounds, I will bet that you'll be giving your engine monitor a lot of attention your next few flights- which is probably also a good idea.

And thanks also for reminding me how important it is to take my time and pay attention when I work, rather than just working fast. Good luck and thanks for sharing.

[nels]

Glad you guys appreciated my post. I almost didn't bother but thought it might help someone out there and maybe it will.