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John, Not being there makes it hard to make an assessment. Anytime I have had an engine spitting and popping it either mean the air/fuel mixture was too lean or I had a ignition problem (mainly timing). I have no experience with any coils other than the stock Mazda but additional cooling certainly could not hurt. It really sounds like to me your engine is increasing rpm until its getting into a region where the air/fuel mixture may be too lean. Normally a too lean engine will pop and spit but not certain if your sputter is same as my sputter {:>). Also you did not mention what boost levels you were running when this was happening.
Ed
Any time my engine acts abnormal, its grounded until I figure out the problem
----- Original Message ----- From: "John Slade" <sladerj@bellsouth.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Monday, May 22, 2006 9:56 PM
Subject: [FlyRotary] Another case of heat-soaked coils?
Yesterday I took a friend for a ride and the engine purred sweetly for the entire trip. Looking back, the only thing different was that there didn't seem to be an rpm drop when I disabled leading or trailing coils during the runup.
Today all was normal during runup (except perhaps the coil disable causing no rpm drop) and full power got me 5300 before I couldn't hold it any more on the brakes. Take-off and climb were normal. On the downwind I was showing 5800 rpm so I decide to coursen the prop. When I did I felt a splutter. I reduced throttle and the engine ran normally. I increased throttle. More splutter. I reduced throttle and it ran normally at 4600. Any more throttle and all I got was reduced power & popping and spitting. I circled the field trying mixture adjustments, checking fuel pressure on both pumps, coil & injector defeat and swapping to B computer. Nothing seemed to make any difference, so I landed.
The only change since the previous flight was that I'd replaced the plugs with a clean set - not new - just clean. Suspecting a bad plug I let the engine cool down a bit, then installed new ones. Later in the day the engine ran fine during taxi and again reached 5300 on runup. Acceleration seemed normal then, halfway through the takeoff roll, I felt a splutter, so I aborted and rolled off the runway.
When I added power to taxi clear of the runway the spitting got much worse. So bad, in fact that it seemed to be running on one rotor and there was insufficient thrust to move the plane forward. I tried adjusting mixture and defeating injectors & coils again and the engine eventually stopped. I was able to restart, but had the same symptoms. The rpm was fairly steady at 1100 or so, but this was the max rpm I could get. The EM2 was flip flopping rpm readings 2300...400...2100..800...every couple of seconds.
I called Tracy from right there on the taxiway. As always - he took the call and listened to my unscientific whining. Thank you Tracy :) Anyway, his best thought was that it sounded like it might be a coil heat-soak problem. It definitely seems heat related, and my cowl has been running a bit hotter since I installed the new T04 turbo.
I pushed (yes pushed) the plane back to the hangar, then tried turning the prop to feel all six compression strokes. To my untrained arm muscles the compressions all felt the same. I ordered 4 new coils and will report if this corrects the problem. Whether it does or not, I see a separate air duct for the coils in my future. The blow tube I installed may not be providing enough cooling. I once tried installing a temp sensor at the coils, but this sent other EM2 temp readings haywire - induced current from the ignition? - so unfortunately I don't have temp readings on the coils.
Anyone have additional thoughts on this?
Sincerely,
Frustrated in Florida (I could add another F at the beginning to help with the .ing alliteration, but I won't)
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