osxuser
Well Known Member
Ok, so I'm gonna just go ahead and call it a Mechrep (like a Pirep, but I'm not the pilot of this particular bird).
One of my customers with an O-360-A1A powered 6a has been fighting high CHT's for the last year or so. It seemed to start after we replaced the carb with an overhauled one, so we did the research, changed the jet, and otherwise made sure the induction system was in good shape.
I went up on a test flight with him after that work was done, only to find some ALARMINGLY high RATE of CHT increase at takeoff power settings. I say this because I fly with the same engine in the Cardinal, and while we have the same high CHT problem, the RATE of increase is a lot more even and slow. At the same time, there had always in the back of my mind been a little warning about what the ignition system was doing, it was acting different than I thought it should on runup, but the owner thought it was fine.
Having eliminated fueling as being the issue, I checked the mag timing, which was of course fine (I say of course, because I've worked on this plane for the last 3 years... timing doesn't just go out that fast typically, and I check it every condition inspection). That left the EI.
The Symptom: On runup, in the past, when the mag was switched off, the RPM would drop dramatically (200ish RPM), than come back up as the EI advanced the timing. What was happening this time, was the EI would lose the 200 RPM, the EGT's would shoot up, and then it would keep slowly loosing RPM until the engine started to bog... Switch back to both and it would come back. My determination was that the computer was for some reason dramatically RETARDING the timing (which was causing the fuel to still be burning when it came out of the valves, thus the sharp rise in EGT).
Once convinced of that, and with no other ideas as to what could be causing the problems, we sent the computer off to Electroair to be checked... just got word today that it was in fact BAD, so we are getting replacements and should have that all back in about a week to retrofit and reinstall. This unit is around 12-15 years old, and has over a thousand hours on it. Not too shabby.
I'll report back when we get the new system installed and wrung out to see if this solves more of our problems, or just the runup issues.
One of my customers with an O-360-A1A powered 6a has been fighting high CHT's for the last year or so. It seemed to start after we replaced the carb with an overhauled one, so we did the research, changed the jet, and otherwise made sure the induction system was in good shape.
I went up on a test flight with him after that work was done, only to find some ALARMINGLY high RATE of CHT increase at takeoff power settings. I say this because I fly with the same engine in the Cardinal, and while we have the same high CHT problem, the RATE of increase is a lot more even and slow. At the same time, there had always in the back of my mind been a little warning about what the ignition system was doing, it was acting different than I thought it should on runup, but the owner thought it was fine.
Having eliminated fueling as being the issue, I checked the mag timing, which was of course fine (I say of course, because I've worked on this plane for the last 3 years... timing doesn't just go out that fast typically, and I check it every condition inspection). That left the EI.
The Symptom: On runup, in the past, when the mag was switched off, the RPM would drop dramatically (200ish RPM), than come back up as the EI advanced the timing. What was happening this time, was the EI would lose the 200 RPM, the EGT's would shoot up, and then it would keep slowly loosing RPM until the engine started to bog... Switch back to both and it would come back. My determination was that the computer was for some reason dramatically RETARDING the timing (which was causing the fuel to still be burning when it came out of the valves, thus the sharp rise in EGT).
Once convinced of that, and with no other ideas as to what could be causing the problems, we sent the computer off to Electroair to be checked... just got word today that it was in fact BAD, so we are getting replacements and should have that all back in about a week to retrofit and reinstall. This unit is around 12-15 years old, and has over a thousand hours on it. Not too shabby.
I'll report back when we get the new system installed and wrung out to see if this solves more of our problems, or just the runup issues.