mvgossman
Filing Flight Plan
I hope an engine guru here can help me with a question regarding a problem I had with my IO-360-A3B6D . It has 1100 hours SMOH.
I was flying my Mooney at 4000 feet, 24 inches manifold pressure, 2400 RPM, 100 degrees rich of peak. A few minutes later I experienced engine roughness developing over about 20 seconds, enough to cause me to change course to the nearest airport. I looked at my JPI engine monitor and found the number 4 cylinder to be at 450 degrees. I went to full rich mixture immediately, and the engine promptly got smooth again over 20 seconds and the CHT went down to its normal level. I landed without incident.
I called my own mechanic and he suggested I just head home on full rich, felt strongly that it was a partially clogged fuel injector nozzle. I decided to leave the plane overnight and drove home because I'm a chicken and darkness was coming in an hour
.
I contacted a local mechanic at a nearby airport, his initial opinion was a sticking exhaust valve but after talking about things further he also concluded a partially plugged fuel injector being to blame. I asked him to go check the engine including borescopes and injector and plug examination. This revealed normal cylinders, normal pistons, normal fuel injectors which he cleaned anyway, and the top plug for that cylinder had an insulator crack. He replaced the plug and pronounced the plane airworthy, with the leading theory being a partially plugged fuel injector.
I flew it home well rich of peak until I was over my home airport, circled the airport trying all combinations of MP, RPM, ROP, LOP, airborne mag checks and everything is totally normal.
I downloaded my JPI data, pertinent portion below.
The basic question I have is, what are the consequences of a partially plugged fuel injector nozzle? Two mechanics were quick to blame a partially clogged fuel injector even after hearing of the CHT of 450 when I noted roughness.
Refer to my engine data with the labelled magenta points, referring to cylinder #3 in brown trace.
1. Normal lean to 100 ROP.
2. Drop in EGT. I’m wondering if that this was moment of the initial partial obstruction of the cylinder 3 injector nozzle that took the mixture even more lean of peak.
3. Rise in EGT as possibly the mixture went to a leaner EGT…
4. ... which coincides exactly where the CHT began rising, maxed out at 484 deg F.
5. About 20 seconds after I noted the rough engine and heading to the nearest airport, I noted the elevated CHT (I think it was 450 on the display) at this point and went full rich with prompt decrease in CHT. I didn’t notice the EGT at the time, but it went down too on the graph.
6. Even at full rich the EGT began to rise here.
7. Perhaps at this point a partially obstructed injector nozzle resolved itself. Everything normal after that.
So here are my thoughts. It seems like these are the leading events possible with a clogged injector.
1. A complete blockage of an injector would cause loss of power, roughness, and low EGT and CHT I would think, so this can be ruled out.
2. A partial blockage resulting in a mixture lean of peak would result in power loss, roughness, lower EGT, and lower CHT. I think this can be ruled out.
3. A partial blockage could result in a leaner mixture resulting in peak EGT, and this may not be good in the long run for the health of that cylinder because CHT would run hotter on that cylinder, but I do not think that it would result in this rapid of a CHT rise nor that peak CHT of 484 degrees F, would you agree?
4. I think that what really happened is that something triggered a detonation or pre-ignition event.
So that’s where I need help. Which came first, the chicken or the egg, and what egg? The detonation may have been triggered by a cracked insulator on that top plug, perhaps provoked by a partially blocked injector resulting in a peak EGT mixture or even lean of peak? Or is the cracked insulator a red herring, i.e. can in fact a peak EGT mixture, presumably caused by injector nozzle blockage, start detonation all by itself and the cracked insulator was caused by the detonation itself?
And regarding preignition, my understanding is that this is a very rapid, catastrophic event, so can we rule that out or could it have been “mild pre-ignition”?
A pilot friend with tons of commercial flying operations behind piston engines says he thinks it’s a sticking exhaust valve. The theory is that the stuck open exhaust valve would result in high EGT and that could cause a falsely high reading from the CHT probe. I could be wrong, but I would think that EGT would go up higher than that or at least fluctuate more wildly, and I doubt that the CHT probe would heat up. Plus, I have no morning sickness symptoms.
I really need your help on what to do next. I spoke with someone at AOPA and he (an A&P) felt that plugged injector and then detonation was the most likely, and that I should get the timing checked. If the timing checks out OK I see no alternative but to fly and monitor.
Mitch
P. S. The format of the AOPA Pilot Information Center that replaces the red board, what do you think of it?
I was flying my Mooney at 4000 feet, 24 inches manifold pressure, 2400 RPM, 100 degrees rich of peak. A few minutes later I experienced engine roughness developing over about 20 seconds, enough to cause me to change course to the nearest airport. I looked at my JPI engine monitor and found the number 4 cylinder to be at 450 degrees. I went to full rich mixture immediately, and the engine promptly got smooth again over 20 seconds and the CHT went down to its normal level. I landed without incident.
I called my own mechanic and he suggested I just head home on full rich, felt strongly that it was a partially clogged fuel injector nozzle. I decided to leave the plane overnight and drove home because I'm a chicken and darkness was coming in an hour
.
I contacted a local mechanic at a nearby airport, his initial opinion was a sticking exhaust valve but after talking about things further he also concluded a partially plugged fuel injector being to blame. I asked him to go check the engine including borescopes and injector and plug examination. This revealed normal cylinders, normal pistons, normal fuel injectors which he cleaned anyway, and the top plug for that cylinder had an insulator crack. He replaced the plug and pronounced the plane airworthy, with the leading theory being a partially plugged fuel injector.
I flew it home well rich of peak until I was over my home airport, circled the airport trying all combinations of MP, RPM, ROP, LOP, airborne mag checks and everything is totally normal.
I downloaded my JPI data, pertinent portion below.
The basic question I have is, what are the consequences of a partially plugged fuel injector nozzle? Two mechanics were quick to blame a partially clogged fuel injector even after hearing of the CHT of 450 when I noted roughness.
Refer to my engine data with the labelled magenta points, referring to cylinder #3 in brown trace.
1. Normal lean to 100 ROP.
2. Drop in EGT. I’m wondering if that this was moment of the initial partial obstruction of the cylinder 3 injector nozzle that took the mixture even more lean of peak.
3. Rise in EGT as possibly the mixture went to a leaner EGT…
4. ... which coincides exactly where the CHT began rising, maxed out at 484 deg F.
5. About 20 seconds after I noted the rough engine and heading to the nearest airport, I noted the elevated CHT (I think it was 450 on the display) at this point and went full rich with prompt decrease in CHT. I didn’t notice the EGT at the time, but it went down too on the graph.
6. Even at full rich the EGT began to rise here.
7. Perhaps at this point a partially obstructed injector nozzle resolved itself. Everything normal after that.
So here are my thoughts. It seems like these are the leading events possible with a clogged injector.
1. A complete blockage of an injector would cause loss of power, roughness, and low EGT and CHT I would think, so this can be ruled out.
2. A partial blockage resulting in a mixture lean of peak would result in power loss, roughness, lower EGT, and lower CHT. I think this can be ruled out.
3. A partial blockage could result in a leaner mixture resulting in peak EGT, and this may not be good in the long run for the health of that cylinder because CHT would run hotter on that cylinder, but I do not think that it would result in this rapid of a CHT rise nor that peak CHT of 484 degrees F, would you agree?
4. I think that what really happened is that something triggered a detonation or pre-ignition event.
So that’s where I need help. Which came first, the chicken or the egg, and what egg? The detonation may have been triggered by a cracked insulator on that top plug, perhaps provoked by a partially blocked injector resulting in a peak EGT mixture or even lean of peak? Or is the cracked insulator a red herring, i.e. can in fact a peak EGT mixture, presumably caused by injector nozzle blockage, start detonation all by itself and the cracked insulator was caused by the detonation itself?
And regarding preignition, my understanding is that this is a very rapid, catastrophic event, so can we rule that out or could it have been “mild pre-ignition”?
A pilot friend with tons of commercial flying operations behind piston engines says he thinks it’s a sticking exhaust valve. The theory is that the stuck open exhaust valve would result in high EGT and that could cause a falsely high reading from the CHT probe. I could be wrong, but I would think that EGT would go up higher than that or at least fluctuate more wildly, and I doubt that the CHT probe would heat up. Plus, I have no morning sickness symptoms.
I really need your help on what to do next. I spoke with someone at AOPA and he (an A&P) felt that plugged injector and then detonation was the most likely, and that I should get the timing checked. If the timing checks out OK I see no alternative but to fly and monitor.
Mitch
P. S. The format of the AOPA Pilot Information Center that replaces the red board, what do you think of it?
