one plug not firing

[eric©]

Just bought a 1991 Explorer 4x4 last week, and it has had a miss, a tick, and a lack of power since the day I got it. It seems that the middle plug on the right side is not firing (number 2 cylinder, I believe). The previous owner said that a plug broke while changing them, and fragments went into the engine. It had a tick ever since, but that was over a year ago (this is only what I was told, I have no reason to believe him, nor doubt him).

I pulled all the plugs, they are all Bosch Platinum, and they looked good. I cleaned them, and put them back in. Wires look good, relatively new. I was pulling wires as the DIS block trying to diagnose what cylinder was missing. The only one that changed the way the engine was running was the middle plug on the passenger side. However, I do see a spark jumping the gap at the coil pack(don't know what it's called, the part that would be replacing the distributor), up to about an inch or so. I went down to the spark plug and pulled the boot. Spark jumping again, but never to the plug. It always went somewhere else, like the plug wasn't even there. I swapped plugs and wires around to rule out bad parts, and got the same results. It would seem as if the plug isn't ground to the head at all, but I checked it with a multimeter, and it's grounding just fine. For the hell of it I ran a thread cleaner down the hole, with no difference in results.

The ticking sounds EXACTLY like the sound the the spark makes when I was pulling wires. I looked at it in a dark garage, but didn't see any arcing. Something else I noticed was that the plug wires are attached in a seemingly odd firing pattern. I tried switching to the "proper" setup that I saw on www.therangerstation.com, and the truck wouldn't even run. This is the way I currently have it set up.

Engine:
654\
321/ front
coil pack
465\
321/ front

Do the early Explorers have a different firing order? Is this the proper way?

I'm thinking that I might have that problem with worn rockers and lifters, which would explain the tick and low power, but the plug not firing (and the spark not jumping to the plug) has me totally stumped.

 

[Opera House]

In the DIS system, there are only three coils and two plugs always fire at the same time. YOU CAN NOT PULL PLUG WIRES TO TEST THE SYSTEM. The plugs are in series. It would be normal to expect that arcing if you removed a plug wire. I hate BOSCH. That part floating around is probably part of a BOSCH plug. I lost parts of BOSCH plugs twice and now I never use them. Some engines just seem to eat them up. Ceck resistance resistance of the plug wires. Anything under 20K is probably ok. Boots should always be regreased with silicone or microcracks/ carbon tracks will develop on the insulator. These require optical magnification to see. I've seen this happen to a plug in as little as 7K. Coatings can also happen on the inside insulator that are difficult to see. For a couple of bucks I'd start off with a new set of Motorcraft plugs. I've fought a lot of plug problems.

 

[monkeydude3]

my best suggestion would be try to get that engine on an engine ignition scope. We have one at my automotive class. You can visually watch how each cylinder is firing. This will tell you what part is bad and exactly on which cylinder... your local shop should be able to do this for you. A shop I have here charged me $70 inspect my engine top to bottom, including the ignition scope, so it would probably cost less if you just have it scoped. It sounds like your coil to me.

George