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High EGT, low CHT

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scrollF4

scrollF4

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Gang,
This weekend while cruising home from an FFI practice, I watched my #1 cylinder?s EGT climb to about 40-50 degrees warmer than the other 3. Simultaneously, the #1 CHT cooled to about 40-50 degrees cooler than the other 3 cylinders.
Jarhead postulated two theories, either of which would make that cylinder run leaner than the others:
1) a possible piece of schmutz in the #1 injection nozzle.
2) a possible air leak in the #1 induction.

I?m unable to return to the hangar for all this week, so I figured I?d hit up the VAF brain trust for theories and pointers to arm my trouble-shooting efforts next week. Thoughts?
 
One plug stopped firing

plugged injector will cause both to go down.
air leak will not cause this type of symptom.

When you drop one plug, your effective timing is retarded. The retarded timing will cause CHT to drop and EGT to rise. Typically see the same across all four cylinders when a mag goes offline.

If you go lean enough to drop the CHT's 50 degrees, for any reason, you will be WELL lean of peak and EGTs would be going down. Or in rare cases, slobbering rich.

I should add that a stuck, bent or crackjed exhaust valve can create symptoms like this, but would expect higher EGTs.

Larry
 
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The symptoms you describe are similar to mine last year going to OSH. After several days of trouble shooting various possibilities, DanH finally found a "bugger" of some kind in the affected injector. Once cleaned out the engine ran normally.
 
If you have Lightspeed ignitions it?s possible for only one side of a coil to fail and drop out one plug. It?s also possible for the coil to operate normally at low altitudes but fail as you climb higher then return to normal on the descent.
G
 
Resolved

Cylinder #1?s lower spark plug had a BB of lead deposit stuck in the gap, preventing a spark, giving the same effect as a dead, fouled, or unplugged spark plug. Cleaned it, all good. Thanks folks. :D
 
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Scroll,

Out of curiosity did you do a mag check? In this case, if I'm not mistaken, it would have be diagnostic. The cylinder would have been cold when "firing" on that plug. Would have even told you which plug to pull.....

I say this having had the same experience with a fouled top plug that allowed popping off the top cowl, quick change and little delay in mission! Nice know when you are on the road

k
 
azonic75 said:
Scroll,

Out of curiosity did you do a mag check? In this case, if I'm not mistaken, it would have be diagnostic. The cylinder would have been cold when "firing" on that plug. Would have even told you which plug to pull.....

I say this having had the same experience with a fouled top plug that allowed popping off the top cowl, quick change and little delay in mission! Nice know when you are on the road

k
Click to expand...

I did do a normal mag check before the flight in question, with everything looking normal. The problem developed in flight, and I wasn't bright enough to do a mag check while airborne. Today I did do a mag check and flew it (all after cleaning the plug). I see how the mag check would have told me which plug to pull, but I inspected them both anyway.
 
mag checks

Be very careful with the in flight mag checks. I do this only as a last resort and only at very low power settings. In the case of the fouled plug, a lot of fuel would accumulate very quickly in the exhaust when operating on the "bad" ignition. Switching back to the "good" ignition will produce a pretty significant flame out the exhaust and possibly some exhaust damage.
 
I doubt this is it but it is worth verifying. The reason I doubt it is because if this is the case, all four of your CHT's would go high.

Since you have two P-mags, I have a couple of questions.

1. Are they controlled with toggle switches?
2. Are they running version 40 or higher?

I ask because if the answers are "yes" to both, then it is very possible that you started with one P-mag grounded and one ungrounded. If this happens with pre-version 40 there is a good chance that one had its timing mark reset.

You may have gotten very lucky and it wasn't off by much.

Before your next flight, pull the cowl and verify the P-mag timing is set to TDC, or wherever you set it, if it is supposed to be clocked.
 
Thanks, Bill,
I?ll check that next time, but I have resolved the problem (see previous post). Thanks for everyone?s help.
 
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