MSnS Extra advice re: wasted spark system

[habib99]

I'm installing a megasquirt system with the MSnSExtra code with direct coil driving (from a 36-1 toothed wheel welded to the crank pulley) on my EA82T.

 

I've got in a bit of a muddle over the firing order and the cylinder rotation, basically with the wasted spark system two plugs spark together at a time, obviously one is on combustion whilst the other is while the piston is down near the crank.

 

So which two cylinders do I wire up to fire together? I'm managed to get myself confused and now I cant think straght about it!

 

If anyone has already done the MSnSExtra with wasted spark I'd be SOoooooo grateful if you would share your wiring setup and even send me a copy of you msq file?

 

here's hoping

[bgd73]

Given you do not want a fire at bdc on intake stroke...

 

1-3-2-4

could be paired as 4 and 1, 2 and 3 to get bdc on fire strokes . So 1 would be firing, 4 is bdc already fired, 3 fires, 1 would be bdc fire stroke,

2 fires with, 3 at bdc just fired, then 4 fires with 2 at bdc.

Wait, now I confused myself...

[GeneralDisorder]

It would seem like 1/4 and 2/3 would be the right choice. When 1 is fireing, 4 is at the bottom of it's power/exhaust stroke. Same with 2/3...... although that means the when 4 is fireing, 1 is at the bottom of it's intake stroke.... so myabe that's not a good combination.

 

Fireing order is 1-3-2-4.... so why exactly does the wasted spark have to occur when the cylinder is at BDC?? My choice would be 1/2 and 3/4 for the wasted spark as that prevents fuel mixture from comming into contact with the wasted spark. 1 is on compression, while 2 is on exhaust, and since the spark fires before TDC, it should never come in contact with cylinder #2's intake charge.

 

Anyway, that makes sense to me - I would go with 1/2, and 3/4.

 

GD

[mikeshoup]

Wasted spark on the EJs goes 1-2, and 3-4 fyi.

[habib99]

ok so 1-2 and 3-4 is probably best - if that 's how the EJs run

 

(is the firing order on EA the same as EJ ?)

 

 

THen I've got the issue of spark timing to work out! The MS can be programed to fire at wahtever angle - based on the crank trigger wheel sensor. Does anyone have a link to a good explanation of how the engine rotates and how the intake/exhaust etc all works, I think I remember seeing technical data in the manual that gave firing angle for each cylinder, I guess I should be able to use that but I need more of a firm understanding of waht actually happens as the engine turns - basic stuff but it always seems to confuse me -not hard!!

 

thanks for advice so far.

[daeron]

It would seem like 1/4 and 2/3 would be the right choice. When 1 is fireing, 4 is at the bottom of it's power/exhaust stroke. Same with 2/3...... although that means the when 4 is fireing, 1 is at the bottom of it's intake stroke.... so myabe that's not a good combination.

 

Fireing order is 1-3-2-4.... so why exactly does the wasted spark have to occur when the cylinder is at BDC?? My choice would be 1/2 and 3/4 for the wasted spark as that prevents fuel mixture from comming into contact with the wasted spark. 1 is on compression, while 2 is on exhaust, and since the spark fires before TDC, it should never come in contact with cylinder #2's intake charge.

 

Anyway, that makes sense to me - I would go with 1/2, and 3/4.

 

GD

 

This is also how Nissan's NAP-Z engine works.. its an inline four cylinder, with 8 spark plugs.. it burns a second spark just after the exhaust valve opens, to burn off any excess vapors as they are being blown out. It helps cut down on emissions. pretty neat to know this is part of MSnS, i havent gotten too detailed in my research there yet.

[habib99]

just used this to try and get clearer in my mind how the 4 stroke works:

http://en.wikipedia.org/wiki/Four-stroke_cycle

 

if anyone has a good flat 4 specific link then please let me know.

[mikeshoup]

The way a flat four works is simple. The front two cylinders are paired, and the rear two are paired, meaning the go up and down with each other.

 

There's a power stroke every 180 degree rotation of the crankshaft.

 

Cylinder 1 is the first to fire (front p/s). While Cylinder 1 is on its power stroke, cylinder 2 (front d/s) is on its intake stroke (they both go 'down'). Cylinder 3 (rear p/s) is on its compression stroke and cylinder 4 (rear d/s) is on its exhaust stroke.

 

Cylinder 3 fires putting it on its power stroke, cylinder 4 is on its intake stroke, cylinder 1 is on its exhaust stroke and cylinder 2 is on its compression.

 

This is repeated with the other side of the engine. There may be other firing orders, but its always the same two cylinders banked together, and its always two on each side fire successively.

 

All subaru flat-4s fire 1-3-2-4 btw.

[habib99]

I've drawn out the piston positions, their movements and stroke function at the beggining of each stroke and it has cleared it all up in my mind. and it matches up with mikeshoup's post.

 

So now I think it is clearer, the spark is just BTDC so firing 1 and 2 together will spark 1 on power stroke and 2 just BEFORE it starts intaking for the intake stroke, so as daeron said, it should be ok, my worry is that the intake fuel might get lit by the wasted spark but otherwise I think 1,2 and 3,4 wasted spark is the way.

 

Confirmed by the EJ's working this way, I think that's decided unless anyone has any doubts, advice to offer, next weekend I'll be attempting the start up so speak now or forever....