Uneven Idle EGT

[201er]

Yesterday I noticed EGT on one cylinder way above the rest while idling on the ground. During run up and in flight they would even out. Did an EGT mag check and all was fine. But idling cylinders 1-3 were around 1020 while #4 was going to 1190. Bad probe? Uneven cooling? Problem?

[jetdriven]

One plug not firing, Mike.   Watch your egt's next time you do a mag check, especially inflight.  They all raise 150 degrees.   

[MARZ]

I notice a variance as well - number 4 is always higher in taxi - gound ops - but all even out under power to within 30

[Bolter]

During flight ops, my EGT's are pretty good (<20°F total variation).   During ground ops, this is not the case.  I am told by a wise A&P that the fuel injection (I have a J-model) is just not that well set up for the idle conditions.  So it is prone to being unbalanced and a running a little rough.  Certianly consistent with what I feel and see on my JPI when on the ground.

-dan

[KSMooniac]

Byron is right... that plug is not firing, or intermittent at best and letting you know now that it is time to have another one ready to go.  I would go ahead and remove it now and test it (measure resistance through the center electrode) and inspect the plug lead as well.

This is another example of the value of an engine monitor for routine operation.  If you didn't notice the high EGT, you would fly along fat, dumb and happy until it failed completely and you had a bad vibration and/or RPM drop on the runup.  Then you would have to troubleshoot the entire system to find out which of the 8 plugs went south.  Instead, you know exactly which plug is failing, and can address it at your home base instead of on a trip somewhere.

I had a similar indication on a trip but the plug was completely dead with no previous warning.  Fortunately there was a mechanic still in his hangar, and he loaned me the tools to remove it and he tested it to verify that it was dead.  Luckily he had a new one on the shelf to sell me, and I was on my way within 30 minutes instead of who knows what.  Without the monitor, it could have been a couple of hours.

[Guillaume]

Quote: tomcullen

During flight ops, my EGT's are pretty good (<20°F total variation).   During ground ops, this is not the case.  I am told by a wise A&P that the fuel injection (I have a J-model) is just not that well set up for the idle conditions.  So it is prone to being unbalanced and a running a little rough.  Certianly consistent with what I feel and see on my JPI when on the ground.

-dan