We have a 2003 Generation 1 Cirrus. We have flown it 500 hours in the last 2 years. We have had a slight pop/miss intermittently that won’t go away. We have new mags on it in last 3 months, thought possibly it was cylinder 1 which we replaced, all plugs have been checked, injectors have been cleaned, and all readings are normal. Oil pressure is good, oil temp is good, cht’s are consistent, EGT’s are consistent, rpms and manifold pressure good. No visible signs of trouble with the engine. It seems to happen at lean out of the engine at cruise. We typically fly 6,000-8,000 ft at 2500 rpm’s from 72-77% of power depending on altitude. It usually likes somewhere between 14.5 and 15 gallons per hour at that. That is 168-169 true and great temps. There is no pop on take off or at a full power high fuel flow settings. The latest mechanic I talked to said, the airplane should not begin to pop even at a lean fuel setting. The engine should run rougher if too lean and cough if very lean, but not pop? Oil usage is good as well. The 2 suggestions I have had lately are injectors or an intake leak at a cylinder? This has been a tough problem to chase and has gone on 6 months with not a lot of answers. Anyone else dealt with this before?
Have you checked the Exhaust system?
Check the exhaust cone in the pipe…Take a bright flashlight and look up the tailpipe, you would be able to see it tilted to the side, it should be center.
It could also be an exhaust header cracked at the flange…
Have you done a LOP mag check at altitude (7500’ to 8500’)?
Sometimes it can be a marginal spark plug. Check the ignition wire springs are clean. I use a green scotch-brite pad to polish the ignition wire springs. Then use a isopropyl alcohol to clean the yellow sleeves.
Here are some pictures: This is a spark plug lead - notice the green oxidation on the wire.
The spark plug spring was also corroded.
Check the spark plug resistance with a multimeter. Typically I’ll see around 900 ohms. If it is much higher, the plug is bad. Most times the issue is oxide on the inside metal contact.
I use a small dremel with a round wire brush to clean that metal contact inside the plug. Takes a minute per plug. Lightly tap the plug to get the metal dust out.
It is also possible there is an ignition wire that is arcing over to nearby metal. One of the ignition wires was pressed against the fuel line. It had left little pits on the outside of the fuel line. The fix was to put plastic spiral wrap around the fuel line.
Look closely at each ignition wire for burns or melted areas. This is where the arc is occurring.
I had a similar issue with my G1 SR20. The first time it occurred after leveling off and setting cruise power. It suddenly started popping. We were finally able to get it to stop by aggressively leaning it out. I took it to a service center and they adjusted the fuel/air mixture ratio setting and that seemed to take care of it. However, the problem presented itself again the following week. Leaning it out made it go away. I took it to another service center that was working on my autopilot and they ended up having my fuel pump overhauled where they stated they found “trash” in the pump.
It has worked flawlessly since having the fuel pump overhauled.
Good luck. I hope you get it sorted out.
Randy
This is great info. I feel this is the closest thing I have heard to what I think it is. It is intermittent and the plane runs awesome outside of that. I may have this done and set up the fuel flow just right too.
Thanks
Brant