operating Lightspeed Ign without MP

[prkaye]

During my annual I discovered that the manifold pressure tube to my Lightspeed Electronic Ignition module (Plasma II+) had come disconnected. Therefore I have been operating my aircraft without MP to the Lightspeed for an extended period of time.
What are the consequences of this? Can operating this way cause other problems or maintenance items that need to be checked?

[Radomir]

It would always run on outside baro pressure, instead of your actual MAP.. therefore you were losing some efficiency.. no damage...

[Pat Hatch]

Originally Posted by prkaye

During my annual I discovered that the manifold pressure tube to my Lightspeed Electronic Ignition module (Plasma II+) had come disconnected. Therefore I have been operating my aircraft without MP to the Lightspeed for an extended period of time.
What are the consequences of this? Can operating this way cause other problems or maintenance items that need to be checked?

Your ignition advance is a function of decreasing manifold pressure (assuming constant RPM), so as you climb and MP decreases, your ignition advances from the base value (usually 25° BTDC) to a maximum advance (can be as high as 42° BTDC). So not having the MP line connected will just cause your EI to act somewhat like a regular mag, fixed timing at 25° BTDC. The advance curves, if you have them, will show the relationship between timing and MP and RPM. Once you fix your MP hose, you should be back in business, no harm done.

[Kevin Horton]

The disconnected MP line would also allow a small amount of air to be sucked into the cylinder which has the MP connection. This would cause that cylinder to run slightly leaner than it would otherwise. The amount of air that was sucked in would depend on the difference between the MP and the pressure at the open end of the line.

Generally speaking, at full throttle, the air leak would be small, as there would be little difference between the MP and ambient pressure. At idle, the air leak would be greatest. This might possible cause that cylinder to misfire at low power, but there should be no damage. At high power, the MP would be high, and the air leak small, so it would cause no harm.