hight egt and cht on one cylinder when full rich

[tectweaker]

I am chasing an issue that I have been noticing more recently.

On take off and climb out I am seeing higher EGT and CHT on one cylinder (#4). New plugs, cleaned injectors - the spread is about 250f higher - the EGT still is lower than 1450 on all cylinders. CHTs are higher compared to other cylinders by about 20-30 degrees.

As soon as I start leaning - the CHTs become super even with other cylinders (within 2-4 degrees) and also the EGT spread drops to within 75-100f.

Essentially leaning makes it super even. Any ideas what might be causing it - I am planning to clean injector on this cylinder again. The engine runs particularly smooth at all rpms, starts great and idles well.

The only thing that was changed most recently was the mixture cable - Not sure if that had anything to do with it.

 

[blaplante]

Do an injector flow test.
and/or swap injectors around

 

[Dugaru]

CHTs are higher compared to other cylinders by about 20-30 degrees.

I don’t think this is at all unusual or abnormal, especially in climb/descent. But if Lycoming or some authoritative source disagrees, I am ready to sit corrected!

 

[DanH]

Essentially leaning makes it super even. Any ideas what might be causing it

Better to test than guess.

Here two tests are appropriate, full rich margin and injector balance.

Rich margin: Fly the plane at 3500 Ft. Set 24 square for power, allow temps to stabilize. Slowly lean the mixture and watch for the first cylinder to peak. Record the peak EGT. Repeat for the second, third and fourth cylinder to peak. Put the mixture back full rich. Wait one minute, then record the full rich EGT for each. Calculate the difference between the full rich and peak EGT values. Assuming certification settings, there should be 185 to 230 degrees F difference in the two readings for every cylinder. Personally I'm happy with 150F for all, closer to best power mixture at full rich. Others want 250, "for cooling". An injector with less spread than the others is a candidate for inspection.

Injector balance: Similar procedure, different goal, requires more time. Climb to an upper altitude, say 8500~9500 so the throttle plate is full open, and set RPM for your typical cruise. Set the EIS/EFIS to a record function, or use a clipboard with five columns. Do not use the EIS/EFIS lean finder function, but rather, just record raw data. Lean the mixture in very small increments, preferably 0.1 GPH. After each adjustment, be patient and allow all EGTs to stabilize. Record the fuel flow and each EGT, then lean another 0.1 GPH. Keep repeating until all the EGT's have risen to a peak and started back down. Back on the ground, plot the data, or just examine the clipboard values and mark the highest temperatures in each EGT column. All EGTs should reach peak within a 0.5 GPH spread, with 0.1 being very good. Nozzle diameters can be changed to adjust the spread. Assuming you're leaning from rich toward lean, a cylinder which peaks significantly earlier than the group is a candidate for inspection.

The only thing that was changed most recently was the mixture cable - Not sure if that had anything to do with it.

Probably not, as it would affect all cylinders, not just one. However, mixture cable travel should be eyeballed anyway I routinely find misadjusted mixture cable rigging which does not allow reaching the full rich or ICO stops on the throttle body.