Emerald 74 4X4
Well-known member
Ok, so I figured out why I'm getting knock under load. I've been pondering this the last couple days and realized that I'm running too much advance under load, somehow. 28 to 36 degrees doesn't seem like too much, but thats what my symptoms were indicating.
So I started playing with the trigger offset in Megasquirt while tuning today. I bumped up the trigger offset by 10 degrees (positive) to retard the timing all over the ignition map by 10 degrees. Lo and behold, the engine ran much better with virtually no knock and I actually got up to 5 psi of boost at one point safely.
So it got me thinking as to why does it seem to run better with 18 to 26 degrees of advance compared to what should be 28 to 36 degrees. Then I realized that the EDIS tone ring is already preset to 10 degrees BTDC. The Megasquirt doesn't know this unless I offset the ignition 10 degrees to get the ignition advance that is what Megasquirt is changing via the ignition map. So by offsetting by 10 degrees, I cancel out the mechanical 10 degrees of the tone ring leaving me with ACTUAL timing that is denoted by my ignition map.
So does anyone follow me on this? I believe I matched the timing light reading to the "big number" in the trigger offset correctly when I first got it running, and the EDIS configuration says to set the trigger offset to "0". But shouldn't it be 10 degrees offset because of the mechanical preset the the EDIS already has?
Does anyone follow me on this?
So I started playing with the trigger offset in Megasquirt while tuning today. I bumped up the trigger offset by 10 degrees (positive) to retard the timing all over the ignition map by 10 degrees. Lo and behold, the engine ran much better with virtually no knock and I actually got up to 5 psi of boost at one point safely.
So it got me thinking as to why does it seem to run better with 18 to 26 degrees of advance compared to what should be 28 to 36 degrees. Then I realized that the EDIS tone ring is already preset to 10 degrees BTDC. The Megasquirt doesn't know this unless I offset the ignition 10 degrees to get the ignition advance that is what Megasquirt is changing via the ignition map. So by offsetting by 10 degrees, I cancel out the mechanical 10 degrees of the tone ring leaving me with ACTUAL timing that is denoted by my ignition map.
So does anyone follow me on this? I believe I matched the timing light reading to the "big number" in the trigger offset correctly when I first got it running, and the EDIS configuration says to set the trigger offset to "0". But shouldn't it be 10 degrees offset because of the mechanical preset the the EDIS already has?
Does anyone follow me on this?