Tankerpilot75
Well Known Member
I reinstalled my repaired PMag and did an engine ignition check and a CHT was low but it’s EGT was normal and aligned with the other EGTs. Suspected a probe problem so swapped with #3.Nothing moved. I then put a heat gun to the #1 probe and guess what - #2 CHT climbed. Put the heat gun to #3 probe - #4 climbed. Checked #2 CHT and #1 climbed.
Decided to check the EGT probes a with the heat gun and they all climbed according to their correct cylinder position. I had just had my EIS worked on by GRT and they had replaced the motherboard to accommodate the change from slick magnetos to PMags. My old EIS didn’t have the TacSen selection that newer EIS monitors have and electronic ignition’s require.
Suspecting an improper wiring somewhere I asked GRT to clarify how to read CHTs on the EIS, left to right/top to bottom OR relative to cylinder position on the engine (left CHTs on EIS screen for cylinders 2&4; right CHTs on EIS screens for cylinders 1&3). Jeff was kind enough to quickly respond and confirmed - read them left to right as shown below.
CHT1 CHT2
CHT3 CHT4
Same with EGTs.
But the CHTs on my EIS were in effect showing the information below.
CHT2 CHT1
CHT4 CHT3
and
EGT1 EGT2
EGT3 EGT4
EFIS data correctly corresponded to how the EIS was displaying the information therefore the “wiring problem” had to be incorrectly wired CHT probes to the EIS. Not an mis-wired motherboard.
Here’s the really bad thing,I’ve never touched the engine monitor/probe wiring in the eight years that I’ve owned the aircraft. I once did replace an EGT probe but EGT probes were correctly wired.
The builder flew it for seven years in this condition. I’ve flown it for eight. Therefore this aircraft has flown 15 years with the CHTs probes incorrectly wired to the EIS monitor and no one suspected a thing. No wonder I occasionally had weird engine observations when I tried to analyze the occasional engine hiccups. CHTs were reporting on the wrong cylinders but EGTs were reporting on their correct cylinders.
How and why this occurred - who knows! But at least the issue is now corrected. It’s amazing what you’ll find when you start really looking at things! RVs are definitely amateur built and maintained. Can’t tell you how many A&Ps / A&P/IAs also have worked on this airplane but it’s been quite a few. When things don’t make sense there’s always a reason.
Decided to check the EGT probes a with the heat gun and they all climbed according to their correct cylinder position. I had just had my EIS worked on by GRT and they had replaced the motherboard to accommodate the change from slick magnetos to PMags. My old EIS didn’t have the TacSen selection that newer EIS monitors have and electronic ignition’s require.
Suspecting an improper wiring somewhere I asked GRT to clarify how to read CHTs on the EIS, left to right/top to bottom OR relative to cylinder position on the engine (left CHTs on EIS screen for cylinders 2&4; right CHTs on EIS screens for cylinders 1&3). Jeff was kind enough to quickly respond and confirmed - read them left to right as shown below.
CHT1 CHT2
CHT3 CHT4
Same with EGTs.
But the CHTs on my EIS were in effect showing the information below.
CHT2 CHT1
CHT4 CHT3
and
EGT1 EGT2
EGT3 EGT4
EFIS data correctly corresponded to how the EIS was displaying the information therefore the “wiring problem” had to be incorrectly wired CHT probes to the EIS. Not an mis-wired motherboard.
Here’s the really bad thing,I’ve never touched the engine monitor/probe wiring in the eight years that I’ve owned the aircraft. I once did replace an EGT probe but EGT probes were correctly wired.
The builder flew it for seven years in this condition. I’ve flown it for eight. Therefore this aircraft has flown 15 years with the CHTs probes incorrectly wired to the EIS monitor and no one suspected a thing. No wonder I occasionally had weird engine observations when I tried to analyze the occasional engine hiccups. CHTs were reporting on the wrong cylinders but EGTs were reporting on their correct cylinders.
How and why this occurred - who knows! But at least the issue is now corrected. It’s amazing what you’ll find when you start really looking at things! RVs are definitely amateur built and maintained. Can’t tell you how many A&Ps / A&P/IAs also have worked on this airplane but it’s been quite a few. When things don’t make sense there’s always a reason.