Intermittent rough running from a mechanical source?
08-12-2019, 06:28 AM
#21
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What fuel are you using in this application? What kind of altitude does the aircraft see?
08-12-2019, 10:42 AM
#22
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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.
08-12-2019, 12:02 PM
#23
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They use 100LL aviation fuel, and only a few thousand feet at the most altitude. The field is at about 900 feet elevation, so maybe 3000 - 4000 ft above sea level when flying. Certainly in the range of a car in the mountains.
08-12-2019, 04:56 PM
#24
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Run this by the mechanics. Have them go into the ECM via HPtuners, or EFILive and turn off the knock sensors. You have plenty of octane in that fuel to resist any harmful detonation. The lead in the fuel can aid in detonation. Perhaps the sensors are picking up detonation and retarding timing? I’m simply thinking out loud here. Not really turning enough rpm to warrant using knock sensors in this application in my opinion...Worth a shot.
Last edited by Che70velle; 08-12-2019 at 06:08 PM.
08-17-2019, 01:26 AM
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It turns out they hadn’t replaced the cam position sensor until today and will fly it again on Monday.
What would be the symptoms of a bad can position sensor? Similar to what we’re seeing, I suspect.
In this airplane the engine is mounted backward and there is very little space between the face of the engine and the firewall. So I imagine it gets pretty hot in there, without the usual cooling air blowing over it.
Not hard to imagine the sensor would overheat.
We’ll see come Monday
Jim
What would be the symptoms of a bad can position sensor? Similar to what we’re seeing, I suspect.
In this airplane the engine is mounted backward and there is very little space between the face of the engine and the firewall. So I imagine it gets pretty hot in there, without the usual cooling air blowing over it.
Not hard to imagine the sensor would overheat.
We’ll see come Monday
Jim
08-17-2019, 03:39 AM
#26
TECH Addict
FWIW,, 100LL WILL ruin O2 sensors.. BTDT with many racers too cheap to buy race gas..
it starts out intermittent and gets worse as the fouling increases. Oh and the lead fouling is really hard to see..
Its the same color as most electrodes, but you might see dark gray streaks on the insulator.
it starts out intermittent and gets worse as the fouling increases. Oh and the lead fouling is really hard to see..
Its the same color as most electrodes, but you might see dark gray streaks on the insulator.
08-17-2019, 12:05 PM
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FWIW,, 100LL WILL ruin O2 sensors.. BTDT with many racers too cheap to buy race gas..
it starts out intermittent and gets worse as the fouling increases. Oh and the lead fouling is really hard to see..
Its the same color as most electrodes, but you might see dark gray streaks on the insulator.
it starts out intermittent and gets worse as the fouling increases. Oh and the lead fouling is really hard to see..
Its the same color as most electrodes, but you might see dark gray streaks on the insulator.
09-10-2019, 01:20 PM
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Update- Replacing the cam sensor made no difference, so they took the heads off and found one pushrod was not quite right. They replaced all the lifters and pushrods but it didn’t solve the problem so they have removed the engine and are going to replace it.
My guess is a valve was sticking in its guide when it got hot, resulting in a bent pushrod and misfire
My guess is a valve was sticking in its guide when it got hot, resulting in a bent pushrod and misfire
10-29-2019, 09:14 PM
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Thanks for all your feedback, guys.
Jim
10-29-2019, 10:33 PM
#31
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Glad you got it figured out, and thankful nobody got hurt in attempting to fly with the hurt engine. Very unfortunate that you got your hands on an engine that was hurt and it ended up in an aircraft of all places. Just don’t see LS engines very often that are defective when new.