While doing the annual "pull the plugs & have a look-see" on both my Subes today, I noticed a pattern. Actually I notice this every time, but the passenger-front and driver-rear plugs alway have erosion of the center electrode that the other two plugs don't have. I'm assuming it's the polarity of the waste spark system.

 

What's odd is that the erosion pattern of the front cylinder bank is opposite that of the rear bank, meaning that the polarity of the front coil is opposite that of the rear coil for some reason. If so, why?

 

**** ******!

I don't know why it would be made that way, but it is possible that the two coils have opposite polarities. It would make more sense to me that both cylinders on bank 1 be straight polarity and bank 2 be reverse. Opposing polarities may be necessary to prevent one coil's magnetic field from negatively interfering with the other, due to the close proximity. I'm no electrical engineer, so I'm only guessing.

Mmm... yeah, maybe to keep the flux generation of one coil from inducing spark voltage in the other.

 

The only other reason would have to be cheaper cost somehow.

 

**** ******!

its the flux generation thing

 

or your flux capacitor is acting up

 

 

 

nipper

its the flux generation thing

 

or your flux capacitor is acting up

 

 

 

nipper

 

(joke)

I thought those things were only on deloreans.

Subaru ran out of plutonium.

Well, I found a diagram in the FSM that shows the paired cylinders sharing opposite ends of the same secondary inductor. So, yes, this should give you the result that you are seeing. This is a simplistic diagram so it may not be accurate, but if it is, it implies a few other things: One of which is that if one cylinder misfires it may cause its paired cylinder to misfire.

Well, I found a diagram in the FSM that shows the paired cylinders sharing opposite ends of the same secondary inductor. So, yes, this should give you the result that you are seeing. This is a simplistic diagram so it may not be accurate, but if it is, it implies a few other things: One of which is that if one cylinder misfires it may cause its paired cylinder to misfire.

 

thats right. and there isnt alot to a coil, so its an acurate drawing.

 

nipper

Accuracy can only be assumed. A similar schematic for the crank position sensor was simplified compared to a fuctional cutaway. It would be easy for the coil schematic to have left off details like a common positive and separate secondary windings.

 

You are probably right, though.

[...]it implies a few other things: One of which is that if one cylinder misfires it may cause its paired cylinder to misfire.

Obviously, it depends on what causes the misfire. First, let's assume it's ignition-related; other causes (such as individual fuel injector problems) won't be "coupled" to the paired cylinder.

 

The paired cylinders are connected in a series circuit comprised of their two plugs, a coil secondary, and the corresponding ignition cables (the block completes the series connection between the ground electrodes). If the miss is due to a fouled plug, that won't affect the other cylinder -- the "wasted" portion of the spark energy can either jump a gap or take a path through fouling material. If the miss is due to a plug whose gap has widened from wear, it likely also won't affect the paired cylinder, since when a cylinder is on the exhaust cycle the plug is comparatively easy to fire. Even ignition cable insulation breakdown would only affect the cylinder whose cable has the defect.

 

What will affect firing of both cylinders is something that reduces the available spark voltage. That could be from a bad coil, increased resistance of either of the paired ignition cables, or an open circuit (break in a cable conductor or disconnected/loose at either end). (If resistor plugs are used, their internal resistance increasing could also be a problem.)

 

So, if misfire of both cylinders in a pair develops simultaneously, it's probably due to a bad (or badly connected) ignition cable to one of the two cylinders, or possibly a defective coil in the pack.