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Hey all,
Looking for some thoughts from the Aerovee brain trust. I have one cylinder (#1, back left) going insanely high, like over 1500F. This is during a full power climb. If I enrichen it to get it below 1400, the engine runs poorly as the other cylinders are too rich. The others average about 1200 in climb. In cruise it will run below 1400, but the others are 1000-1200. I have swapped the EGT probe from the #1 and #2 cylinders and the high temperature stays with the #1 cylinder. I've also swapped inputs on the MFD and again the high temperature stays with #1. So I believe it's too hot and I'm not seeing an instrumentation error.

This happens on just the mags, or on both ignitions. I did not try on the secondary ignition only.

I did reseal the left intake manifold, but no change. It seems an induction leak would be a potential cause of a high EGT.

In reading other forums a bad exhaust valve is listed as a possibility, or head gasket, or cylinder issue.

My recent compression test was 116/119/126/125. Last year was 119/121/125/119.

I'm thinking of pressuring the intake with a shop vac to look for a leak with soapy water. Otherwise I'm thinking of pulling the head to have a look.

Any thoughts welcome.

Edit: I also checked the #1 valve last on the exhaust.

Don't know if this would cause it, but is the exhaust gasket on that cylinder good? I've had to replace them more often than I expected.

Screw the electronics............What story do the spark plugs tell?

I'll check the exhaust gasket. They are the originals.

Plugs are coming out, stand by...

Another thing to look at is the intake manifold gasket security. if one bolt isnt as tight as the other, there may well be just one cylinder sucking air. I have saftied those bolts and have not had any of then come loose any bit. The other thing to consider is the probe may be at fault, if nothing else is found. The plug will also tell you , comparing to one of the other cylinders plug, if cylinder is actually very lean. Pleas e let us know what you find!

n502pd wrote:Another thing to look at is the intake manifold gasket security. if one bolt isnt as tight as the other, there may well be just one cylinder sucking air. I have saftied those bolts and have not had any of then come loose any bit. The other thing to consider is the probe may be at fault, if nothing else is found. The plug will also tell you , comparing to one of the other cylinders plug, if cylinder is actually very lean. Pleas e let us know what you find!

Joe,
I redid the intake sealing on that side, so it was secure. Maybe there is a warp or crack, I'm not sure.
I did swap probes, and the high EGT stayed with cylinder #1.

What are the corresponding CHT's while #1 is displaying the unusual high temp?

Lou,
My #1 CHT failed. It reads around 100F after the engine warms up. Pretty much everything else was under 200F. It was cool out. Oil temp was 161.

Edit: I assume it has failed. I'm going to do a differential compression test today.

Bryan, you didn't mention so I won't assume. You did verify both the top and bottom plugs are firing ok - right? Only one plug firing will give a hot egt as fuel burns slower and gets out the exhaust before it's ready.