I have similar issues with my Seneca engines tsio360. Idle at 700-800 very rough and egt on 2 cylinders drops to 500-600 so suspect those aren’t firing well. Have changed the plugs to fine wire, done the M0 adjustments. Once above 1000 smooth as silk. In flight GAMI check all within 0.4 gph. MAP on left is higher at idle around 18”, vs 15” on right. Engine doesn’t die but nevertheless have set idle at 800 just in case and just leave it at 1100-1200 during ground ops for now. Planning on checking for induction leaks next month during annual. Also replacing all of my rocker cover gaskets as well so will get a look at the valves. Borescope has been fine. Any other troubleshooting tips would be appreciated.
Todd, I seriously think this thread and your determination has driven a key outcome. Lot's of great ideas from everyone on what to look for and your excellent follow up on what was actually found. Your efforts will save fellow pilots $10's of thousands in troubleshooting related expenses as well as all the downtime. Thanks again!
Which two cylinders is the EGT low? Is the EGT balanced in flight? Around 1000 rpm the turbo starts to kick in and the engine runs noticeably smoother. With the split in MP at idle it could be an induction leak too. Most operations in a Seneca are at atmospheric pressure or better so induction issues are only seen at idle.
You should also check your prop as Todd has discovered but with the EGT drop and MP split it is more likely an engine issue for you.
I am asking which cylinders as I believe opposing cylinder intake valves are powered from the same cam lobe so it would suggest a cam lift issue. Adjacent cylinders are more likely an induction leak in the runners. Also look for fuel staining around the injectors.
For the TSIO-360 at idle you can also press the prime button and it will go to the alternate spray rail in the induction rail. Does it run better this way? If it does I would look at the injectors and the air fittings to the injectors. FYI, there is a SB to replace this system as it cuts off flow to the injectors and diverts it to the prime jets which is not enough to keep you in the air if the system failed. Never press prime in the air... asking for trouble.
I’ll have to double check which cylinders but definitely #1 and #2. #6 isn’t great either. The intake valve opening is an interesting idea. The SB has been done so that isn’t it. I was wondering about the o rings on the injector air fittings. In flight everything is smooth and fairly even so I also suspect intake leak, but a bit more trouble to check on the turbo. Not sure how to pressurize the intake side to bubble test.
Thanks for the comment. I really appreciate it. I am going to start the trouble shooting on the amp issue this coming week. I will post as I discover any developments on the issue.
How recent was the SB? I ask because part of the SB is changing the injector drains to a taller fitting. If there is a leak in the cylinder drain path then there would be an air leak at idle. You could also have a stuck check valve (underside of engine by oil drain). If this was stuck open you would have a MP rise.
If there is an issue with injector air fittings I would suspect poor atomization of fuel too.
You can measure intake valve lift with a dial indicator by taking the rocker covers off.
After the prop overhaul the vibration was reduced quite a bit. There was still some but mild. The shop did a final balance and it was a bit better. There is still a little vibration that is totally acceptable.
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I have similar issues with my Seneca engines tsio360. Idle at 700-800 very rough and egt on 2 cylinders drops to 500-600 so suspect those aren’t firing well. Have changed the plugs to fine wire, done the M0 adjustments. Once above 1000 smooth as silk. In flight GAMI check all within 0.4 gph. MAP on left is higher at idle around 18”, vs 15” on right. Engine doesn’t die but nevertheless have set idle at 800 just in case and just leave it at 1100-1200 during ground ops for now. Planning on checking for induction leaks next month during annual. Also replacing all of my rocker cover gaskets as well so will get a look at the valves. Borescope has been fine. Any other troubleshooting tips would be appreciated.
Todd, I seriously think this thread and your determination has driven a key outcome. Lot's of great ideas from everyone on what to look for and your excellent follow up on what was actually found. Your efforts will save fellow pilots $10's of thousands in troubleshooting related expenses as well as all the downtime. Thanks again!
Eric Panning
1981 Seneca III
Hillsboro, OR (KHIO)
Tokir,
Which two cylinders is the EGT low? Is the EGT balanced in flight? Around 1000 rpm the turbo starts to kick in and the engine runs noticeably smoother. With the split in MP at idle it could be an induction leak too. Most operations in a Seneca are at atmospheric pressure or better so induction issues are only seen at idle.
You should also check your prop as Todd has discovered but with the EGT drop and MP split it is more likely an engine issue for you.
I am asking which cylinders as I believe opposing cylinder intake valves are powered from the same cam lobe so it would suggest a cam lift issue. Adjacent cylinders are more likely an induction leak in the runners. Also look for fuel staining around the injectors.
For the TSIO-360 at idle you can also press the prime button and it will go to the alternate spray rail in the induction rail. Does it run better this way? If it does I would look at the injectors and the air fittings to the injectors. FYI, there is a SB to replace this system as it cuts off flow to the injectors and diverts it to the prime jets which is not enough to keep you in the air if the system failed. Never press prime in the air... asking for trouble.
Eric Panning
1981 Seneca III
Hillsboro, OR (KHIO)
Eric
I’ll have to double check which cylinders but definitely #1 and #2. #6 isn’t great either. The intake valve opening is an interesting idea. The SB has been done so that isn’t it. I was wondering about the o rings on the injector air fittings. In flight everything is smooth and fairly even so I also suspect intake leak, but a bit more trouble to check on the turbo. Not sure how to pressurize the intake side to bubble test.
Empannin,
Thanks for the comment. I really appreciate it. I am going to start the trouble shooting on the amp issue this coming week. I will post as I discover any developments on the issue.
Thanks again.
How recent was the SB? I ask because part of the SB is changing the injector drains to a taller fitting. If there is a leak in the cylinder drain path then there would be an air leak at idle. You could also have a stuck check valve (underside of engine by oil drain). If this was stuck open you would have a MP rise.
If there is an issue with injector air fittings I would suspect poor atomization of fuel too.
You can measure intake valve lift with a dial indicator by taking the rocker covers off.
Eric Panning
1981 Seneca III
Hillsboro, OR (KHIO)
Those are good points and not things I would have thought of. Thanks. Will add those to the list of things to check.
So here is the final outcome.
After the prop overhaul the vibration was reduced quite a bit. There was still some but mild. The shop did a final balance and it was a bit better. There is still a little vibration that is totally acceptable.