Spark plug issue / questions RV-10

Last week I flew to lunch in the -10, and had a rough engine just after takeoff.

EFIS data showed #6 cylinder not firing on the R mag.
Pulled the plugs, top plug (R mag) had very weak spark in the bomb tester.

Replaced the plug, went flying this evening.

In flight mag check ... #6 is good on both mags, but now #5 goes cold on the L mag. Mag check on the ground is totally fine.

Seems a bit odd for a coincidence, but the engine and plugs are ~2008 vintage (Lycoming from Van's) and first flew in 2016. Stuff I've read online seems to hint that Champion had some plug issues in years past.

I haven't pulled the #5 top plug yet, but the failure mode is exactly the same.

I'm thinking of just replacing all the plugs with Tempest plugs.

What are most of you -10 guys using? The chart shows both the -38 and -40 as applicable, is there a plus / minus to either type of plug?

Thanks in advance.

The -38 and 40 refer to heat ranges. Too hot you risk pre-ignition. Too cold, you pick up more deposits. I use -38.
How many hours on the plugs? When were they last cleaned/gapped/rotated?

I have found lots of failed Champion plugs from that vintage. I have been replacing them with Tempest plugs. I bet if you checked them on a resistance tester you will find they fail.

Vic

Bob-
These are -38Es
Cleaned gapped etc during the panel upgrade / annual last winter. Total 153h, probably 50 or so since annual (tach time).

Vic -

Thanks for the input. I did check resistance; the old #6 plug failed (open), and interestingly the new champion plug I replaced it with also read open on the meter, but runs fine in the engine. There seem to be varying opinions on the utility / relevance of the resistance test for champion plugs. Any thoughts on that?

Should I just stick with the 38 temp plugs? Any benefit to fine wires?

Fine wires will fire better, are more resistant to fouling, and, in the long run, are cheaper (since they last longer). Just don?t drop one.

TShort said:

Bob-
These are -38Es
Cleaned gapped etc during the panel upgrade / annual last winter. Total 153h, probably 50 or so since annual (tach time).

Vic -

Thanks for the input. I did check resistance; the old #6 plug failed (open), and interestingly the new champion plug I replaced it with also read open on the meter, but runs fine in the engine. There seem to be varying opinions on the utility / relevance of the resistance test for champion plugs. Any thoughts on that?

Should I just stick with the 38 temp plugs? Any benefit to fine wires?

Click to expand...

They will still fire with high resistance, but it is eating your points in the mag. The cost of fine wires can turn some people off, and I understand that. You could also try some UREM37BY plugs. They work much better in a fouling condition.

I get you cleaned and gapped them 50 hours ago. I would honestly get rid of them.

Vic