Starting from a stoplight, all of a sudden truck started missing and check engine light came on. On my way to autozone for a code check I noticed under hard acceleration the miss seemed to disappeared, but soon as I resumed speed truck shook like crazy.
1-6-8 were showing misfire, grabbed new wires and plugs [they didn't have copper] so they said the autolite app5224 platinum would work.
When i got to #8 i figured that was my problem....wire cracked and plug porcelain was broke and lodged in gap.
Done dodge tsb wiring routing w/convolute.......and truck runs very rough.

note: check engine light off now
142K miles on engine
Hughes plenum kit installed 2 months ago
haven't done a compression check

platinum plugs??

 

Some engines don't like the platinum plugs..... You could swap 'em out, and see if that helps.....

 

copper plugs [RC12LC4]didn't seem to help much. Idles better, but i'm sure it's a definite miss now. Tried induction timing light on each wire...getting fire on all eight.

 

I'd go for distributor cap and rotor just on principle. If your wires were in that kind of shape, chances are good that the rotor and cap are every bit as old and are in need of replacement. Not to mention that the failed plug might have caused arcing in the cap, which may have blown away some conductor and/or left a carbon trail. A strobe on the timing light tells you that the spark happened, but not if it was as strong as it should be or at the right time.

If cap and rotor don't fix it, it's time to get the codes cleared and see what shows up as pending after running for a bit.

 

No change with new cap and rotor..........Am I correct: if check engine light is off...all codes are cleared? If not, will leaving batt. disconnected a couple hrs. clear them?

....I'm starting to get a bad feeling, think maybe something happened in #8 that caused that plug to crack


btw, great forum!!

 

Yeah, disconnecting the battery will clear the codes. Disconnect it and turn on some electrical load -- the dome lamp will do the trick -- to bleed off any stored charge. I usually do that first, then get my tools and lights and fender blankets and whatnot set up so there's plenty of discharge time.

So, cap and rotor, no change. It's good to have 'em off the suspect list, anyway. Was the distributor shaft nice and solid, or did it have some side-to-side play in it?

Have you done anything else to the truck since the plenum kit? Inspected the wiring to ensure that you didn't pinch or break something (like the #8 injector wiring)? Is there any chance you blocked a water passage? When it's running rough can you hear any abnormal mechanical noise?

I've begun to wonder if the plenum gasket's leaking again. It seems a good time to use the factory method to test for it (with a vacuum/pressure gauge, that is), and follow up with a compression and leak-down test.

I'm thinking that if heat caused the failure of the #8 plug and wire, which seems most likely, and there are no blocked water passages or problems indicated by the compression/leak-down/plenum gasket tests, that cylinder is running wickedly lean. I'd start by inspecting the plug that's in there now to see what it has to say, and then the injector (first with a stethoscope, then if a problem is indicated test it and its control circuit electrically, and if the electrical tests are okay, pull the thing for inspection and/or replacement).

I wouldn't run the engine any longer than necessary for testing, since overheating a cylinder is the quickest route to discovery of how easy it is to crack these magnum heads.

 

Thought I'd pull the 8 and 6 [not 7] before I called it a night.....plugs have abt. 8 miles on them. As u can see #8 is very wet and #7 is like new.

will try again tomorrow...

 

That's way to much buildup in eight miles..... or are those the old plugs?

 

The image isn't quite large enough to get much information other than the color. Is that fuel or oil that's wetting it?

 

Yep...brand new plugs. #8 was as white as the other one 8 miles ago. Not sure abt. if it's oil or gas...been out of cylinder a hour or so and still wet on one side.

I'm wondering if there's crud not letting a valve close now. I'm almost positive that plenum was blown a couple years before I bought the truck [previous owner said it used a little oil for some time]