Glad you are skeptical about the propeller theory. I'm not aware of a principle of physics whereby propeller-induced vibration mitigates above idle speed.
BTW, after my valve-induced vibration odyssey a few years back, my A&P (who has a lot of Adam Savage in him) and I performed an experiment trying to evaluate the potential impact of all the different vibration causes the experts had proposed. One-by-one we replaced my low-resistance Tempest plugs with high-resistance Champion ones, tuned the fuel system to the extremes of M-O, deliberately put the GAMI injectors in the wrong cylinders, adjusted the ignition timing to the extremes of range, removed intake gaskets to cause leaks, and everything else we could think of except maybe drilling holes through the cylinders or removing the crankshaft balance weights. Then we evaluated the results of each configuration by observing vibration and engine monitor readings throughout the entire range of RPMs with the engine de-cowled. The results....wait for it....nada! None of these defects made any visually observable or measurable difference in engine performance.
I was reminded of this experiment by Scott's article in the magazine this month, evaluating the performance of speed modifications. If you haven't seen his article, you should! I am hoping to repeat the vibration study, fully-instrumented and on the dynamometer, and write an article like Scott did. We all can benefit from more objective (and factual) troubleshooting information.
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.
The prop was installed yesterday and according to the mechanic, the test run was a success, no more vibration at idle!!! Smooth at all rpm's. A big sigh of relief. I haven't flown it yet but will let everyone know how that pans out next week.
The last problem I am still trying to figure out is the high amp reading I encounter during flight.
Thanks everyone,
Todd
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.
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.
Those are good points and not things I would have thought of. Thanks. Will add those to the list of things to check.
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.