Hello all 

I have a 2ltr zetec as supplied in the kit from 12 years ago and I have removed the plugs for replacement and found them to be of two different types . Now I did not note which cylinders they came from so need to know if the replacements need to be 2 different types and if so what they need to be as the plugs are motocraft and which type goes in which cylinder

Hope you can help 

Chris D 

Thread on fordownersclub.

 

It appears Henry installs the two types of plugs when the engines are supplied new, it's something to do with the wasted spark ignition, and there is a correct position for each type, being:

 

Timing belt end P1 / PG1 / P1 / PG1

 

Special thanks go to Jonathon Kay for his BM and link to

 

www.fordownersclub.com

I found this topic very interesting, so did a bit of digging and soon found the reason. When the same coil is used to generate the two sparks the plugs are wired in series with the secondary coil between the two plugs. The current flow for the spark starts in the engine block, travels from the outer part of one plug to the central electrode, then through the secondary winding to the central electrode of the other plug and back to the block via the outer part of the plug. This difference in electron flow through each plug means that the erosion behaviour in each is different, one plug has +ve central electrode other has -ve central electrode, so the central electrode metal alloy is different. The diagram below makes it all clear.

 

Edited October 21, 20241 yr by Sparepart
change diag

The vast majority on modern 4 and 6 cylinder engines use wasted spark and use the same plugs in all positions. The makers just expect owners to replace the plugs more often.

The platinum plugs ford fitted originally are not cheep but will last a long time.

That's a bit of an odd situation, having two different types of plugs in the engine! Typically, all four spark plugs in a 2.0L Zetec engine should be the same type, and it's strange that two different ones were used