High #4 egt @ runup and drops @ mag check

[Clparker23]

Here’s another one, I got my 67’ F from my first annual, we did not change plugs, but we did replace a sheared through bolt on #3-#2!! First flight, I noticed a slight roughness @ mag check, thought it was a fouled plug, cleared it, mag checked good. Then 2 flights later I started to notice #4 egt running quite a bit higher on the ground at runup and then had a failed mag check and #4 dropping egt on right mag. I changed plugs and got new tempest massives. 10 hours later I’ve got the same scenario...it’s high egt on #4 and just a tick high on #3, then on right mag check #4 drops egt below all the others and pretty rough.

 

Is this a plug again, a lead wire in the harness going bad or something worse?

 

I did clean #4 injector and line today BTW.

 

Thanks in advance!

 

 

 

 

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[gsxrpilot]

 

One of the plugs in #4 isn't firing. Could be the plug, or the wire. I'd check the plugs first. I'm not familiar with your engine, but the Right Mag will run the top plugs on one side and the bottom plugs on the other side. Work this out and you'll know exactly which plug/wire is the problem.

When the single plug is firing, the EGT for that cylinder will be higher than if both plugs were firing. When the single working plug is off (no plugs firing) the EGT for that cylinder will drop off and the engine will run really rough. 

[MARZ]

It’s also good practice to lean excessively for ground ops. 

[Clparker23]

Thanks GSXRpilot, that’s exactly what I’ve been reading but I did want to double check. I’m going to swap plug on top #4, and see what I have from there.


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[Clparker23]

After the first time I had this happen, I’m leaning to the point of near stumble in ground ops.


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[MIR2018]

Before changing the plugs again, how about moving plugs to a different cylinder and see if the trouble moves to that cylinder?

[Clparker23]

Before changing the plugs again, how about moving plugs to a different cylinder and see if the trouble moves to that cylinder?

I believe that’s what I’m going to do, move #4 top to #2 top.


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[Clparker23]

I swapped #4s to #2s, I did clean what appeared to be a little deposit on top #4 before the swap. Mag checked out fine.

I’m ordering fine wire tempest for all 8 next time I need something from spruce.


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[Hank]

2 hours ago, Clparker23 said:

I’m ordering fine wire tempest for all 8 next time I need something from spruce.
 

Better price them things first! Lots of people run fine wires in the bottom only. Some of us still run Champion massives . . .

Hint:  one Champion massive spark plug costs more than a set of 6 for my truck. Approx. the same delta applies going from massives to fine wire.   

[jaylw314]

11 hours ago, gsxrpilot said:

 

One of the plugs in #4 isn't firing. Could be the plug, or the wire. I'd check the plugs first. I'm not familiar with your engine, but the Right Mag will run the top plugs on one side and the bottom plugs on the other side. Work this out and you'll know exactly which plug/wire is the problem.

When the single plug is firing, the EGT for that cylinder will be higher than if both plugs were firing. When the single working plug is off (no plugs firing) the EGT for that cylinder will drop off and the engine will run really rough. 

IIRC, on the IO-360, each mag fires the lower plugs on the same side and the top pugs on the other side.  Don't quote me because I always forget and always forget to write it down...

[Clparker23]

Better price them things first! Lots of people run fine wires in the bottom only. Some of us still run Champion massives . . .
Hint:  one Champion massive spark plug costs more than a set of 6 for my truck. Approx. the same delta applies going from massives to fine wire.   

Man I know, I was going to replace with fine wires 10hrs ago and my cheapness went massive. Is there anything wrong with running fines in just #4 top and bottom?


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[gsxrpilot]

Typically the bottom plugs are the ones that have problems. You could just run one fine wire in the bottom of #4. Or as most do, run fine wires in the bottom of each cylinder  and massives in the top.

[jaylw314]

17 minutes ago, Clparker23 said:

 

 

Man I know, I was going to replace with fine wires 10hrs ago and my cheapness went massive. Is there anything wrong with running fines in just #4 top and bottom?


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I run fine wires on the left mag (tops on right, bottoms on left).  The advantage is that the fine wires are rotated amongst themselves with the normal plug rotation at annual, so the configuration stays the same and less likely someone makes a mistake.  The other advantage is having all the fine wires on the left mag, which has the starter impulse coupling on the A3B6, but I don't think that matters in the A3B6D, right?