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Tankerpilot75

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.
 
TankerPilot, recently on a RV-9 I worked on, I discovered the same thing.. I de-pinned the connector and had to relocate every pin to get the CHTs and EGTs correct..

Tell me more about the PMAGs and the tach connection.. I too have an older EIS and am about to put on Pmags. I just assumed the tach function would pick up the correct signal..
 
Taltruda said:
TankerPilot, recently on a RV-9 I worked on, I discovered the same thing.. I de-pinned the connector and had to relocate every pin to get the CHTs and EGTs correct..

Tell me more about the PMAGs and the tach connection.. I too have an older EIS and am about to put on Pmags. I just assumed the tach function would pick up the correct signal..
Click to expand...

Your fix is exactly what I had to do except I only de-pinned CHTs, labeled the wires and re-arranged. This was extremely difficult because of the limited space I had to work in - not enough service wiring.

There are several EIS setting changes required when you upgrade to electronic ignition systems. PMags rpm signal strength is weaker than a traditional magneto (particularly at lower rpm’s) and the GRT EIS manual mentions that electronic ignitions may need to increase the Tach sensitivity signal by removing a resistor and changing the TachSen setting from low (L) to high (H) - section 7.7 in EIS manual. You also need to change your TachP/R setting from 1 to 2 pulses per revolution.

In my case the PMag rpm signal would drop to zero when engine rpm’s fell below 1,000 rpm. Older EIS monitors lack a TachP/R2 setting (only have TachP/R1), and lack both TachSen1 and TachSen2 settings. Therefore to get rpm readings below 1,000 rpm, required in my case, either GRT to “adjust” the sensitivity of my EIS or an upgraded motherboard. I elected to upgrade the motherboard - $450! Of course I later discovered I would also have to re-calibrate my Aux3 and Aux4 L/R fuel tank configuration settings because of the new motherboard. Law of unintended consequences. Major pain in the rear!

I then had an infant mortality issue with the left PMag (bearing too tight) which became very difficult to diagnose and explain correctly to PMag tech support because of this CHT probe misalignment with EGT probes correctly installed. Thankfully EMag Ignition said to just send the PMag to them and they would look at it. Their turnaround was quick.

After re-reading this post I realized I failed to mention the real hero in this saga, my friend Dan Burdette. He has an RV9A with one PMag and knows more about engines and ignition systems than I will ever know. He assisted me with this troubleshooting and was actually the first to identify the CHT misalignment.
 
Last edited:
Tankerpilot75 said:
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.
Click to expand...

According to my EIS install manual, you can wire them any way you want, in fact they mention wiring it the way yours is because the cylinder positions correspond with what you’re seeing from the cockpit: CHT 2 & 4 on the left - 1 & 3 on the right. Mine is wired with 1 & 2 on the to and 3 & 4 on the bottom - I think - at least that’s the way I thought I was doing it. I’ll check the next time I have my cowl off. I would actually prefer to have it displayed the way yours is.
 
Scott Hersha said:
According to my EIS install manual, you can wire them any way you want, in fact they mention wiring it the way yours is because the cylinder positions correspond with what you’re seeing from the cockpit: CHT 2 & 4 on the left - 1 & 3 on the right. Mine is wired with 1 & 2 on the to and 3 & 4 on the bottom - I think - at least that’s the way I thought I was doing it. I’ll check the next time I have my cowl off. I would actually prefer to have it displayed the way yours is.
Click to expand...

If you have a GRT EFIS then your engine CHT readings using the other wiring (my previous CHT wiring) would display cylinder #2 as cylinder #1, #3 as #4, etc. The GRT EFIS cannot be configured to read them right to left. If it could I would have just changed EFIS configuration settings.

Jeff Defow, at GRT, indicated several requests have been made to have EFIS configuration changes to accommodate this orientation but GRT has elected to continue with the left to right approach. If you don’t have a GRT EFIS then the other wiring approach will work just fine.
 
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Tankerpilot75 said:
If you have a GRT EFIS then your engine CHT readings using the other wiring (my previous CHT wiring) would display cylinder #2 as cylinder #1, #3 as #4, etc. The GRT EFIS cannot be configured to read them right to left. If it could I would have just changed EFIS configuration settings.

Jeff Defow, at GRT, indicated several requests have been made to have EFIS configuration changes to accommodate this orientation but GRT has elected to continue with the left to right approach. If you don’t have a GRT EFIS then the other wiring approach will work just fine.
Click to expand...

Yep, I didn’t think of that - good call. I’ve wired mine as the manual suggests, so my EFIS will match, not that I considered that when I wired it and set it up. Looks like I limped into it. My first EIS (20+ years ago) was stand alone - no EFIS.
 
Very common on dual mags, is to find the left switch position is actually checking the right and the right switch position is checking the left...Easy to do, if you forget the switch is making on the mag you are not checking.
 
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