fluctuating EGT

[KCKS]

The last two flights my #1 EGT has been fluctuating. Has anyone seen this? How often are you changing the Denso plugs? Any ideas? 180 hours/FX3

[Andy]

The fluctuating EGT readings are likely caused by an intermittent open circuit of the ground wire between the sensor and the GEA 24. (I had a similar problem with a CHT sensor on my new FX-3)

You ask about plugs in the same post but I doubt spark plugs have anything to do with the EGT issue. I have not changed my plugs (FX-3 132 engine hours). Gaps were as new at first condition inspection.

[aeroaddict]

Agree, open circuit somewhere.

In regards to plugs, a bad plug (or associated wiring) is easily identified on run up.

For the CC340 on the EX-2, manual states to inspect and clean the plugs every 100hrs. I just replace the plugs every 100hrs because they are cheap (Sparkplugs.com, Rock Auto, ....).

[KCKS]

Agree, open circuit somewhere.

In regards to plugs, a bad plug (or associated wiring) is easily identified on run up.

For the CC340 on the EX-2, manual states to inspect and clean the plugs every 100hrs. I just replace the plugs every 100hrs because they are cheap (Sparkplugs.com, Rock Auto, ....).

There is no loose wiring that I could find. I tested the resistance of the plugs. Plug from top of cylinder #1 was 6 times the normal readings of the other 7 plugs. The runup was normal, so this bad plug was not easily identifiable. I've ordered a new set. I expect that will fix the problem.

[KCKS]

There is no loose wiring that I could find. I tested the resistance of the plugs. Plug from top of cylinder #1 was 6 times the normal readings of the other 7 plugs. The runup was normal, so this bad plug was not easily identifiable. I've ordered a new set. I expect that will fix the problem.

This was a very instructive problem. The high power run-up showed no RPM change when switching between 1 and 2. However, the fluctuating EGT temperatures did indicate a problem. I put in new plugs and problem solved.

[Andy]

This was a very instructive problem. The high power run-up showed no RPM change when switching between 1 and 2. However, the fluctuating EGT temperatures did indicate a problem. I put in new plugs and problem solved.

Thanks for the report. I had not realized that a misfiring plug would raise the EGT but here is an extract from a Savvy Analysis report that I received in my email today:

“If one of the #2 spark plugs had stopped firing, we would expect to see EGT #2 rise by about 50°F to 100°F and CHT #2 start to decline a bit."

[KCKS]

So Andy gave me a chance to plug Savvy analysis. It's a great service, relatively inexpensive and they are excellent diagnosticians. I just use the EGT analysis, but they just added FX3 to their full maintenance service. They are the ones that figured out my problem