tomhanaway
Well Known Member
Lycoming IO-375.
Working through a very rough running No. 1 cylinder at rpm’s below 1000 rpm. EGT cold on 1 until after 1000 rpm when engine runs smoothly.
Engine ran fine for 175 hours. New, consistent issue. Engine hot or cold.
So,
Likely possibilities.
Fuel, spark, exhaust valve, induction leak(?).
Fuel flow test at idle and full throttle setting is equal for all four cylinders. Pulled apart AFP fuel divider anyway and it seems clean.
All new spark plugs (tested in spark plug pressure box), all harness wires ohm tested. Dual P mags sent back to emagair for checkup. Still waiting on those.
No. 1 cylinder is 80/80 on compression test. Borescope shows exhaust valve moving and nice burn pattern on face of valve.
Before I tear apart valves, is it possible to be having a valve issue that would cause rough idle with full compression and moving valves ?
I keep suspecting something in fuel flow at idle but not sure what else to check since flow for all cylinders is identical.
Thanks,
Tom Hanaway
Working through a very rough running No. 1 cylinder at rpm’s below 1000 rpm. EGT cold on 1 until after 1000 rpm when engine runs smoothly.
Engine ran fine for 175 hours. New, consistent issue. Engine hot or cold.
So,
Likely possibilities.
Fuel, spark, exhaust valve, induction leak(?).
Fuel flow test at idle and full throttle setting is equal for all four cylinders. Pulled apart AFP fuel divider anyway and it seems clean.
All new spark plugs (tested in spark plug pressure box), all harness wires ohm tested. Dual P mags sent back to emagair for checkup. Still waiting on those.
No. 1 cylinder is 80/80 on compression test. Borescope shows exhaust valve moving and nice burn pattern on face of valve.
Before I tear apart valves, is it possible to be having a valve issue that would cause rough idle with full compression and moving valves ?
I keep suspecting something in fuel flow at idle but not sure what else to check since flow for all cylinders is identical.
Thanks,
Tom Hanaway