Intermittent rough running from a mechanical source?
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Teching In
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Intermittent rough running from a mechanical source? If this is not the right forum for this, please let me know.
I have an LS3 430 installed in a Titan T-51 airplane. It has an intermittent rough running problem whereby it will run fine for 40 minutes or so then start to run rough and the plane has to be landed. The next day it is fine at startup but the same thing happens when it is flown. It uses a Link Xtreme G4+ ECU and is not overheating. The ECU does not have closed loop lambda sensing and does not report any problems. The engine is rev limited to 300hp, with about 4000 rpm or less being used at takeoff and 3000 or less at cruise
They have replaced the ECU, plugs, wiring harness, coils, and injectors without change, so they are thinking it could be a mechanical problem with the engine. But I’m not aware of any mechanical problem the that could present this way.
Is is there something about the mechanical makeup the LS3 engine that could cause this?
i think it has to be an electrical problem, either via spark or fuel.
thank you.
Jim
I have an LS3 430 installed in a Titan T-51 airplane. It has an intermittent rough running problem whereby it will run fine for 40 minutes or so then start to run rough and the plane has to be landed. The next day it is fine at startup but the same thing happens when it is flown. It uses a Link Xtreme G4+ ECU and is not overheating. The ECU does not have closed loop lambda sensing and does not report any problems. The engine is rev limited to 300hp, with about 4000 rpm or less being used at takeoff and 3000 or less at cruise
They have replaced the ECU, plugs, wiring harness, coils, and injectors without change, so they are thinking it could be a mechanical problem with the engine. But I’m not aware of any mechanical problem the that could present this way.
Is is there something about the mechanical makeup the LS3 engine that could cause this?
i think it has to be an electrical problem, either via spark or fuel.
thank you.
Jim
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It does data log but apparently nothing that helps them figure out the problem. It does not sense or record misfires
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Thank you.
Jim
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I was hoping he was going to say he logged fuel pressure but I would think an airplane would have a specific requirement for it's fuel cell. I see some parts changed but not Cam/Cranks sensor, If it's capable of logging it should show a fuel pressure or sensor issue. I can't think of any mechanical issue that would only show up after a long period of time and clear up on it own once it sat for a length of time.
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Mechanic states they do not log fuel pressure, but the plane has 2 pumps and the pilot is a very experienced test pilot. I’m sure he would look at that gauge if misfiring occurred. But I’ll text him anyway.
Yeah i cant think of a mechanical problem that would do this. Replacing the engine is not going to help.
if, say, a valve stopped opening or stayed open, it would either bend the pushrod and/ or destroy the rocker arm / assembly or contact the piston and be bent. ( I assume this is an interference engine.)
BTW, my mechanic says the cam sensor was replaced
Yeah i cant think of a mechanical problem that would do this. Replacing the engine is not going to help.
if, say, a valve stopped opening or stayed open, it would either bend the pushrod and/ or destroy the rocker arm / assembly or contact the piston and be bent. ( I assume this is an interference engine.)
BTW, my mechanic says the cam sensor was replaced
Last edited by Panrdino; Jul 20, 2019 at 01:30 PM. Reason: Add info
Mechanic states they do not log fuel pressure, but the plane has 2 pumps and the pilot is a very experienced test pilot. I’m sure he would look at that gauge if misfiring occurred. But I’ll text him anyway.
Yeah i cant think of a mechanical problem that would do this. Replacing the engine is not going to help.
if, say, a valve stopped opening or stayed open, it would either bend the pushrod and/ or destroy the rocker arm / assembly or contact the piston and be bent. ( I assume this is an interference engine.)
BTW, my mechanic says the cam sensor was replaced
Yeah i cant think of a mechanical problem that would do this. Replacing the engine is not going to help.
if, say, a valve stopped opening or stayed open, it would either bend the pushrod and/ or destroy the rocker arm / assembly or contact the piston and be bent. ( I assume this is an interference engine.)
BTW, my mechanic says the cam sensor was replaced
Was the cam sensor replaced due to a reading/logging issue, or simply a shot in the dark type of deal?
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If this is not the right forum for this, please let me know.
I have an LS3 430 installed in a Titan T-51 airplane. It has an intermittent rough running problem whereby it will run fine for 40 minutes or so then start to run rough and the plane has to be landed. The next day it is fine at startup but the same thing happens when it is flown. It uses a Link Xtreme G4+ ECU and is not overheating. The ECU does not have closed loop lambda sensing and does not report any problems. The engine is rev limited to 300hp, with about 4000 rpm or less being used at takeoff and 3000 or less at cruise
They have replaced the ECU, plugs, wiring harness, coils, and injectors without change, so they are thinking it could be a mechanical problem with the engine. But I’m not aware of any mechanical problem the that could present this way.
Is is there something about the mechanical makeup the LS3 engine that could cause this?
i think it has to be an electrical problem, either via spark or fuel.
thank you.
Jim
I have an LS3 430 installed in a Titan T-51 airplane. It has an intermittent rough running problem whereby it will run fine for 40 minutes or so then start to run rough and the plane has to be landed. The next day it is fine at startup but the same thing happens when it is flown. It uses a Link Xtreme G4+ ECU and is not overheating. The ECU does not have closed loop lambda sensing and does not report any problems. The engine is rev limited to 300hp, with about 4000 rpm or less being used at takeoff and 3000 or less at cruise
They have replaced the ECU, plugs, wiring harness, coils, and injectors without change, so they are thinking it could be a mechanical problem with the engine. But I’m not aware of any mechanical problem the that could present this way.
Is is there something about the mechanical makeup the LS3 engine that could cause this?
i think it has to be an electrical problem, either via spark or fuel.
thank you.
Jim
I thought about that being an issue, but the pilot would see it clear up as altitude decreased upon descent to land.
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That was their first thought - inadequate fuel tank venting / flow capacity, so they enlarged the fuel hose diameter and checked the venting. That was a YEAR ago. Then winter came to Ohio and nothing happened for 10 months.
Launching!
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could be fouling the plugs at altitude and thats why it doesnt clear up on descend? really doesnt sound like a mechanical issue, agree it would just run rough all the time
first post says its rpm limited to 300hp/4k rpm at take off and 3k rpm at cruise, fueling will be drastically different at 7500'+ didnt notice if he mentioned that ecu uses a map sensor, said no closed loop so i imagine someone has tuned it for sd?
installing a wideband o2, even temporarily, would atleast point you towards mechanical or fuel/spark issue
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More info: there are actually 2 levels of misfire. One will go away if you back off the throttle but the other only goes away if you shut the engine down. If you then restart sometimes it’s there and sometimes it isn’t. And neither appears until you have been flying for about 30 min. Varies between 27 and 33 min.