I need to know a little more about my engine than my Haynes manual seem interested in telling me.

Looking from the front, which plugs are my ignition plugs? I assume the other bank of plugs is for burning the exhaust emission. Which coil is the "A" coil pack?

In searching this forum I have come across very few posts pertaining to the 2.5. Is this engine one of Ford's "better ideas" that didn't last long on the production line?

 

What year?

 

The SOHC 2.5L is just a stroked and/or bored 2.3L from 95-later, though the 8 plug head engine had tweaks made to it for the 95 model year that set it apart from the 94-earlier version. Still a Lima 2.X engine, but not quite the same.

Ford got the Duratec 2.3L DOHCer in for the 2001.5 model year, which was an upgrade at least on paper...not dissing on the Duratec, but ~400 lb 4 cylinders make me feel better than those that are 1/2 that weight.

 

All eight spark plugs are used by the ignition system.

Eight spark plugs (two per cylinder) and two ignition coil packs are used in the 2.3/2.5L twin-plug engine. The two ignition coil packs are triggered by the ignition control module and are timed by the PCM.

 

BTW:

DO NOT rely on the Haynes to give you the correct plug order. Just take one off at a time. They have the spark plug order wrong in the Haynes. I found out that cylinders 2 & 3 were switched after who knows how long.

 

Dual plug heads were used in the Rangers from 1989 thru 2001. Four plugs in two cylinders fire at the same time. Nope, I ain't crazy.

In each end of the secondary winding in the ignition coil a spark plug is attached. On the compression stroke, both plugs fire in #1 cylinder igniting the fuel mixture. At the same time, the two plugs in #3 cylinder fire what is called a "waste spark." Due to the high compression in #1 cylinder the electrical resistance is very high. As a result, the ignition system must generate a very high voltage for the spark to jump the plug gap. There is no compression in #3 cylinder, so there is little resistance, and there is very little voltage needed to jump the gap. This acts a kind of a ground circuit for the secondary coil. Repeat for each cylinder, and you have a running engine. Several mfg use this method.

Why? Emissions. Two plugs give a earlier, more complete burn with less residual unburned gasses. It also gives slightly more power due to more energy being used in the fuel charge. Probably not measureable by the seat-of-the pants dyno, but its there. It has nothing to do with burning exhaust gasses(??).