912 ULS strange issue
in 912 / 914 Technical Questions
8 years ago
we have a 912ULS, starts very easily, no problem there, idle and low power while taxiing, no apparent issues, runups and ignition checks show nothing abnormal, the usual RPM drops, and a little bit of roughness. EGT's all fine
full power RPM seams fine, though a little down on power, did not climb as well as it should.
reduce power to cruise RPM, usually 5100 rpm, and it ran very rough,
turned 1 mag off, ran Very rough, mag back on, back to normal roughness, other mag off, nothing changed, just usual roughness, check other mag off again, Very rough again, but this time noticed #2 EGT drop to half the usual value. mag back on, back to the usual rough, by this time i was downwind, and returning to the airport, EGT#2 was still low, and roughness as before, then suddenly the roughness went away, well, not totally, but went to a more smooth, but slight roughness, #2 EGT returned to normal in line with the other 3 cylinders.
We had this issue on the second last flight, and before todays flight, replaced and gapped all the spark plugs to manual specifications, replaced 1 suspect spark plug lead cap. when replacing the plugs, we noted that #1 cylinder plugs, 1 was wet with fuel, and the other a black sooty colour, all others were fine, we figured this was due to a very loose plug lead cap, and replaced it.
obviously that was not the problem....
Hoping someone here might have had a similar issue, or know of a possible known fault and where to look before we go replacing the ignition system.
thank you
full power RPM seams fine, though a little down on power, did not climb as well as it should.
reduce power to cruise RPM, usually 5100 rpm, and it ran very rough,
turned 1 mag off, ran Very rough, mag back on, back to normal roughness, other mag off, nothing changed, just usual roughness, check other mag off again, Very rough again, but this time noticed #2 EGT drop to half the usual value. mag back on, back to the usual rough, by this time i was downwind, and returning to the airport, EGT#2 was still low, and roughness as before, then suddenly the roughness went away, well, not totally, but went to a more smooth, but slight roughness, #2 EGT returned to normal in line with the other 3 cylinders.
We had this issue on the second last flight, and before todays flight, replaced and gapped all the spark plugs to manual specifications, replaced 1 suspect spark plug lead cap. when replacing the plugs, we noted that #1 cylinder plugs, 1 was wet with fuel, and the other a black sooty colour, all others were fine, we figured this was due to a very loose plug lead cap, and replaced it.
obviously that was not the problem....
Hoping someone here might have had a similar issue, or know of a possible known fault and where to look before we go replacing the ignition system.
thank you
