Help with understanding inflight Mag check #'s

Darren S · #1 02-03-2012, 08:06 PM

I fly an RV-7 with a Superior IO-360. Engine has 570 hours. Plugs are 70 hours old. Mags were rebuilt 70 hours ago.

My biggest concern are my findings on Cylinders #1 and #3 for the Ignition Stress test. I did the test 3 times. I was LOP on all cylinders. Readings are degrees F.

My findings(average) : Left Mag only gave readings of 290, 90, 230, 85 for cylinders 1, 2, 3, 4 ( the engine ran really rough too)
Right Mag only gave readings of 144, 165, 110, 168 for cylinders 1, 2, 3, 4.

Mike Busch says that the temp. rise should be 50-100*F. The Right Mag I can live with for now but the #1 and #3 on the Left Mag are out in "left" field (no pun intended)

Possible causes: Left Mag timing ? , ignition wires? , plugs even though they are pretty much new and were just cleaned 12 hours ago?

Any advice and suggestions welcomed.

Thanks.

Darren

PIN 37 · #2 02-03-2012, 08:23 PM

Plugs can be checked easily by changing the location of the plug and see if the low temp follows the plug.

Dave Stephens · #3 02-04-2012, 02:01 AM

Sounds like your injectors are not matched. Remove and clean them (they pick up debris) but dont go poking lock wire through them! (number them so they go back where they came from)

You can check them by putting them in identical bottles and running the pump, after a few seconds you should have the same level of fuel in each bottle

Try that, if that don't work, swap the injectors about and see if the problem goes where the injectors go.

Also maybe you are just trying this too lean, the injectors are never going to be 100% the same

Dave

Darren S · #4 02-04-2012, 06:57 AM

Thanks for the suggestion Dave but I think the injectors are ok. I did the GAMI Mixture Distribution Test and all was well. A reading of 0.4 gph between the first cylinder to peak and the last cylinder to peak. Normal is around 0.5 gph.

The Temperature delta, which I posted is my concern for cylinders #1 and #3. A rise in temperature between 50 - 100 degrees from dual mag to single mag operation is normal. Mine was near 300 degrees.

Without any other ideas I might try rotating some plugs, as was suggested earlier and if that doesn't work then try the ignitions wires. Or just leave it all and just go fly, she runs fine as far as I can tell. BTW ground mag checks show a drop of 90 RPM on both mags

Thanks for the help so far,

Darren