GRT EIS/EGT Problem - need help with diagnosis
Hello everyone! This is my first post; I've been lurking for a some time as I was shopping for my RV7-A (which I purchased last month). This community is amazing and I hope that some day I'll have something to contribute - other than $.
Anyhow, on to the problem...
Immediately following the pre-buy inspection, I flew the ferry pilot back to his home base in my new plane, N811AK. On the return flight, cylinder #4 EGTs were occasionally exceeding the limits and reading about 200 degrees hotter than the other 3 cylinders. The temp on #4 fluctuated right along with the other 3 cylinders, but was always hotter. I figured the problem was bad probe, and continued flying 20 hours until my first oil change.
I brought the plane back to my mechanic (same buy who did the pre-buy) for the oil change. When we uncowled the plane, I almost fainted when I saw the upper spark plug lead for #4 laying on the cylinder, unplugged. The mechanic failed to replace the lead when doing the inspection! We figured this explained the high EGTs: unburnt fuel was combusting in the exhaust causing high temps. We pulled the plug, blasted the lead off and replaced the plug. I flew home after the oil change expecting normal EGTs but #4 was still reading hot.
Next, I swapped the #2 and #4 EGT probe and found that this resulted in the high EGT reading moving over to cylinder #2, indicating a bad probe. I ordered and installed a new probe, but am getting the same high readings with the new probe. It would seem the problem is somewhere between the EGT probe and the EIS.
So, the question is...what's the problem, how do I confirm it, and how do I fix it? Your thoughts are very much appreciated.