Concerning Coils & Cars

You Need Fuel, Air & Spark. El Cap, Pick Only Two!!

Here's a quick look at the present issue facing El Capitan's truck. Not every car manufacturer has gone to a coil-on-plug design, but it's getting to be fairly common.

Back in the day, the engine gnomes would bore a hole through the block up towards the top of the cylinder, thread the hole, and insert a spark plug. On some engines, they were on the side, somewhere near the exhaust manifolds. Other ran down from the top.

You'd run your spark plug wires from each plug to the distributor cap, which was connected to the crankshaft via a gearing system. As the crankshaft turned, the distributor rotor would spin, sending current from the single ignition coil to each plug in turn, firing the plug as the cylinder reached full compression.

If you wanted to dick with somebody's ride, you'd get under their hood and pull the cable from the coil to the distributor cap, and they'd be going nowhere. If you REALLY wanted to be evil, you'd rearrange the order of the spark plug wires.

Some motorhead got the idea to improve reliability and timing by putting a coil on each plug, eliminating the distributor altogether. Instead of one coil, you have eight, and suddenly changing your spark plugs requires a Masters in Mechanical Engineering.

Here's why:



The bottom arrow is the spark plug. Instead of sticking out the side of the block, it's buried 6-8 inches deep in the cylinder head. The long bracket above the bottom arrow is the coil-on-plug assembly.

So, looks pretty easy to get to, right? Just lean in and yank em out?

Not so fast, Sparky...

Here's the 1 thru 4 cylinder bank on the F-150:



The red arrow points to the coil on Cylinder 4. You can see #3 behind it. #1 & #2 are buried under hoses, cables and brackets. In fact, to even get a single one off, you need to pull the silver bracket, remove the vacuum and oil breather hoses and dismount the fuse cover. Complete PITA, but do-able, if you've got long skinny gibbon arms, which I emphatically do not.

Want a real giggle? Here's the other cylinder bank. Look on my works, ye grease monkey, and despair!!



#6 coil is barely visible. #5 you can get to, #7 & #8 need a teleportation unit to remove, I surmise.

Again, back in the day, you could get a set of spark plugs, wires, a new distributor cap and rotor for less than $50. Now each coil-on-plug assembly runs about $100, though you can get them cheaper if you shop around. This is why I didn't replace all of them in one fell swoop.

So, that's the scoop, my little chickadees. Back when I could sit on the fender and hang my feet inside the engine compartment, I could get to all the little fiddly bits. Nowadays? Not so much. It's gotten a lot more crowded under the hood, and as I've said, svelte fingers ain't in my inventory.