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Low CHT with normal EGT’s….

edhunter

Well Known Member
So last week I took my daughter up flying and noticed my #1 CHT was running around 100 degrees cooler than the other 3. This is an IO-320 with 1 mag and 1 lightspeed ignition. I could also sense the power seemed off a bit. We landed, and doing a mag check I could tell the engine was dropping rpms. Thinking I might have a fouled plug I ran the engine up and leaned it out, but the #1 cylinder stayed cold. Like 160 degrees.
I pulled the plugs - they looked ok but I replaced them anyway. They had around 400 hours on them as I could find no mention of plugs being replaced in the logbooks. Plane is new to me as of May and has a total of 396 hours on it since engine was new. Anyway replaced the plugs, cleaned the injectors, and ran the engine up again. No change, #1 still cold. I checked the sensors by putting each in a cup of boiling water, and all measured appropriately. Compression check showed 4 consistent cylinder pressures. Finally checked the intake bolts and sure enough the #1 intake bolts were loose! Snugged them up (on all 4 cylinders), and ran engine up again. Voila’ - problem fixed. CHT and EGTs back to fairly consistent.
I like simple solutions. Thanks to VAF for guidance found here.
Ed
 
while a leaking intake will make a mess of things at partial throttle and worse at idle, it should have very little impact on mixtures at WOT with an FI system. Total fuel flow will be down a bit, but shouldn't see individual differences in the cylinder with the intake leak at WOT.

I suspect you had both a leaking intake AND a partially blocked injector on #1 (typically reduces CHT quite a bit without a significant change in EGT, though are often down a bit from normal). You wouldn't have noticed the difference after cleaning it unless you ran it at WOT and suspect you didn't, as the intake leak showed it's ugly head at run up levels due to th vacuum. The intake leak creeps in over time, where the injector blockage just shows up one day. Pretty difficult to have an intake leak create a "not here yesterday; here today" problem without something being cracked or broken.

If the flight in question was done at low MAPs, then it could have been at intake leak. But if anywhere near WOT, it is more likely the injector.

Larry
 
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