That seams like a cheap way of cutting corners while making some improvement otherwise. I don’t put it past Ford to do what works without fiddling with things unnecessarily.
It’s so odd that 97-98 would have different plugs considering they aren’t using the same coil.
The reason plugs would need to be different would either be thermal differences or the use of dual-output coils. I see this in motorcycles often.
Thermal:
In the case of bikes such as the Honda Magna, it is a transverse V4 engine. This means that one bank is directly in the air stream, the other relies on the liquid cooling as it gets little air. Because of this difference in thermal conditions, the rear cylinders are jetted for fuel differently and use different plugs than the front cylinders.
Dual-output Coils:
Coil-packs have dual-outputs. This means that a spark is made at two leads at the same time. Yes, this is what’s used in a wasted spark system most often. This is not because a wasted spark is required, but because the use of coil-packs has the side effect of a wasted spark.
One issue with coil-packs is that the spark has a bias due to polarity. The spark will always jump from one ground strap, through the coil and to the other ground strap. When I pull the plugs in any dual-output ignition system, it’s clear that one has material transferred to the ground strap and the other has material missing from the ground strap.
So with these two being the only reasons I could explain the necessity for different plugs, and only one that I know of that applied to any Mark VIII at a time, it makes no sense to me that the one conditon which no longer exists in 97-98 Marks still require different plugs.
The ONLY explanation that makes sense now is if Ford decided to match the polarity of the new COP’s to the polarity of the coil-packs. I have no clue why this would be necessary....because it isn’t, but that is the only explanation I can come up with.
To prove this, I would need to see the plugs for the COP’s.
If the ground wire is in the same pin position for every connector, then every COP has the same polarity. If not, then my theory is correct and we may require the different plugs.
Of course, if the polarity is swapped on some coils, you could just swap the pins and the spark would always jump TO the ground strap as it should.
Yes I have autism.
When I was a mechanic, I sometimes had to test polarity because I would use unorthodox methods for repair. This sometimes mean using coils from different brands than the motorcycle. But nobody specifies which wire is which, so I would just test polarity and run it. Most often it was the Yamaha XS coils that were best for old bikes. Really good stuff. But the Chinese versions actually have reversed polarity...sometimes! So I’d have to check every coil to be sure I was installing them the right way.
If it was strong enough I could see which side of the spark was fatter or flared, or I could stick something conductive in between them and see which side flared.
Or to check without undoing any wires, I could run a voltmeter parallel to the plug that’s in the head. It would either read positive or negative with every spark. If it was positive, it was correct, but I had to make sure my probe wires were oriented correctly as well.
I know I talk to much.
