sprucemoose
Well Known Member
I?m in the middle of trouble shooting an ignition problem. I think I?ve got it figured out, but I?d like to get some more opinions. Here?s the relevant facts:
Engine: Superior/ Aerosport O-360, LSE Plasma II on right side, Slick 4371 impulse coupled mag on the left side. About 350 hours since new on everything.
A couple weeks ago, I noticed two problems start at the same time. #1 is that the tach indication on the Grand Rapids EIS4000 was erratic, going up and down by several hundred RPM. This happened intermitantly, at speeds from idle to full power, with a cold or warm engine. At the same time, the engine began having fouled plugs (or what I believed was fouled plugs) which it has never done. A minute at high power leaned out would generally clear up the ?fouled plug.?
The ?fouled plug? problem is now believed to be something other than a fouled plug. The fact that it started happening at the exact same time as the weird tach behavior, leads me to believe that it?s a magneto problem. The EIS4000 takes it?s tach signal from the P-lead of the left mag, run through a 27K ohm resister. I have checked the wiring from mag to switch to EIS. I replaced the resister (it checked out OK, but I replaced it anyway.) I swapped out the EIS for a known good unit, and it did the same thing.
Having tried all the easy stuff, I pulled the mag. Under the supervision of the local A&P greybeard, we pulled it apart. Everything looks good in the mag. The point gap was just slightly over spec so we fixed that. The coils ohm?d out good (I forget the readings, but we looked it up and it was good.) Everything else looked good, so we cleaned it and buttoned it up.
Today was my first chance to fly it since. At startup, the tach was going up and down several hundred RPM, but the engine ran fine on the mag at runup power, so I took it up. In flight, at cruise power, the engine ran very roughly on the left mag alone, as though it was stumbling and missing. It obviously ran just fine on both. I switched the EIS reading to show all 4 channels of EGT, and switched to the left mag. The engine ran very roughly, but all 4 EGTs made a slow, steady climb of 30-40 deg, which is normal behavior. If it were one cylinder not firing and causing the rough running, I would expect the EGT to drop.
I played around with power settings, and found that the engine only ran rough on the left mag at power settings above 18? or so. Below that power, it ran just fine. Obviously it ran just fine on both ignitions, so I am ruling out any fuel or induction problems.
I have an idea in mind as to what the problem is, but I?d like to hear some opinions before I take the next step.
Engine: Superior/ Aerosport O-360, LSE Plasma II on right side, Slick 4371 impulse coupled mag on the left side. About 350 hours since new on everything.
A couple weeks ago, I noticed two problems start at the same time. #1 is that the tach indication on the Grand Rapids EIS4000 was erratic, going up and down by several hundred RPM. This happened intermitantly, at speeds from idle to full power, with a cold or warm engine. At the same time, the engine began having fouled plugs (or what I believed was fouled plugs) which it has never done. A minute at high power leaned out would generally clear up the ?fouled plug.?
The ?fouled plug? problem is now believed to be something other than a fouled plug. The fact that it started happening at the exact same time as the weird tach behavior, leads me to believe that it?s a magneto problem. The EIS4000 takes it?s tach signal from the P-lead of the left mag, run through a 27K ohm resister. I have checked the wiring from mag to switch to EIS. I replaced the resister (it checked out OK, but I replaced it anyway.) I swapped out the EIS for a known good unit, and it did the same thing.
Having tried all the easy stuff, I pulled the mag. Under the supervision of the local A&P greybeard, we pulled it apart. Everything looks good in the mag. The point gap was just slightly over spec so we fixed that. The coils ohm?d out good (I forget the readings, but we looked it up and it was good.) Everything else looked good, so we cleaned it and buttoned it up.
Today was my first chance to fly it since. At startup, the tach was going up and down several hundred RPM, but the engine ran fine on the mag at runup power, so I took it up. In flight, at cruise power, the engine ran very roughly on the left mag alone, as though it was stumbling and missing. It obviously ran just fine on both. I switched the EIS reading to show all 4 channels of EGT, and switched to the left mag. The engine ran very roughly, but all 4 EGTs made a slow, steady climb of 30-40 deg, which is normal behavior. If it were one cylinder not firing and causing the rough running, I would expect the EGT to drop.
I played around with power settings, and found that the engine only ran rough on the left mag at power settings above 18? or so. Below that power, it ran just fine. Obviously it ran just fine on both ignitions, so I am ruling out any fuel or induction problems.
I have an idea in mind as to what the problem is, but I?d like to hear some opinions before I take the next step.