Cross-firing between the 7 and 8 wires

Stever89

5 Year Member
Dec 14, 2009
536
9
39
Biloxi, MS
Never thought much about this, in fact it never entered my mind that this could cause damage, but apparently it can. I was surfing the web reading up on spark plug looms and different ways or arranging the spark plug wires.

Here's a post form another Mustang forum:

"What I'm referring to is inductive crossfiring between the #7 and 8 wires.The standard firing order is 15426378. As the #7 plug fires, the #8 piston is almost halfway up the cylinder, the absolute worst possible place for a spark. If the two wires are too close to eachother and not shielded enough you can get an inductive kick in the #8 wire which can fire off the plug, causing extremely premature ignition. As pressure increases due to bothcombustion andthe piston rising, the mixture eventually explodes all at once (aka detonation) long before the piston reaches TDC. The resulting detonation combined with the force of the piston still trying to move up can cause severe engine damage, especially if it's repeated several times.

Moral of the story: keep the #7 and #8 wires as far apart as possible
"

I've owned many SB Fords, never thought about this, and as far as I know, have never needed to know about it :shrug: I guess now that I'm aware of it I'll make sure to separate them, not across the bay from each other, but a little further apart than normal. I see it's more likely to happen if you're running an HEI (which I am) and your plug wires are past their service life.

Just a heads up in case you didn't know :)
 
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