Dakota - #5 misfire and spark plug problems

1997 Dakota 3.9L w/ 170k miles. Sorry in advance; for me to explain this thoroughly will require a lengthy post.
Two years ago I did my 150k mile (and most recent) complete tuneup,
and when I went to remove spark plug #5 at that time, it just about wouldn't budge. I don't recall having any such spark plug problems before... but for some reason at 150k miles that #5 was a bear to remove. I did get it out, and to my surprise the threads on the plug looked ok w/ no extra metal or chewed threads. Then when I went to put the new plug in (with anti-seize), it wouldn't finger tighten past about 1 or 2 revolutions. I carefully tightened it the rest of the way with a socket, and it was rough going but I got it tightened and never had anymore problems with it... until now.
Over the past few days I've noticed a definite misfire under acceleration, but it isn't constant... it comes and goes. Well today I pulled a P0305 #5 misfire code. I put new wires on and it made no difference. I inspected inside the distributor cap and everything looks uniform (ie #5 doesn't look any different than the others). So I hesitantly tried to remove plug #5, and just like last time, it's really hard to turn. I backed it out about 1 revolution and then chickened out - it wasn't getting easier, it actually started getting harder to turn.
I am fairly (but cannot be completely) sure that I never cross- threaded it - I always finger tighten the plugs. I'm perplexed because the plug threads looked ok after I fought to get it out last time. I've come up with 4 potential explanations for this new misfire:
1) Some plug holes just become stubborn, and maybe I inadvertantly damaged the plug's insulator while trying to get that new #5 installed last time, and maybe it's now starting to bleed voltage in a short circuit on occasion. This is my best case scenario.
2) Maybe the threads did get damaged or crossed despite my finger tightening rule and despite the threads looking ok last time I had the plug out after fighting with it. Rust or crud could have hitched a ride into the threads 2 tuneups ago and welded the plug in place. The idea here is that it's losing compression or something due to screwed up threads. (Can damaged threads do that? Maybe time for a helicoil?)
3) Could be coincedental. Maybe injector #5 is clogged or bad.
4) Could be much worse... worn or damaged valve or seat, blown head gasket, cracked head, etc.
So I suppose my question to you all is, does it sound like the "stuck" #5 plug could be related to my new #5 misfire? Which, if any, of my 4 explanations sounds most valid? Any suggestions? I'm scared stiff at the thought of trying to remove that plug right now.
thank you... dakota2112
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dakota2112 wrote:

If you got two turns on it before putting a wrench to it I don't think it would be crossthreaded. Have you routed the wires like it shows in this TSB? http://dodgeram.info/tsb/1998/18-48-98/18-48-98-v8.htm
--
Ken



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You may want to try squirting some WD-40 on the exposed threads of that plug (there isn't much room but there may be enough to get some into the threading area); let it sit for an hour or so to penetrate some; then try to ease it back in to the head just a little - 1/4 to 1/2 turn or so. Squirt more WD-40 on it; wait an hour or so; then try easing it out some - 1/2 to 1 full turn. Repeat that back in and out process until you get it out. If you get it out without messing the threads up then get a thread restoring tool and try to screw that in to the head and see if it helps. You may want to turn the crank to get that piston to TDC before you start to help keep the crap from going too far down into the calendar. If you can vacuum or blow out the crap after you get that plug out it will help.
Any other suggestions from others on how to get that plug out without breaking anything? I've never had that problem before but have heard of others having it though. I am way over due. The only tune up I've done in the past 10-15 years was on my 55 Chevy during it's restoration. I put a new set of plugs in my 98 Dakota when I replaced the water pump at 90k miles but didn't have to. The existing plugs looked good and they were the original ones.

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Sounds like a chunk of carbon got in the threads or a small hunk of dirt. Either way go get a can of PB Blaster. And a propane torch (or OX/AC) Pull the plug wire. Blow any loose crud out from the plug pocket. Now use the torch to heat up the plug base and the head around it. Get it as hot as possible. Now remove the flame and spray the PB on the plug base (it will SMOKE and might ignite, just blow it out) let it set a while. Then repeat and then use your wrench on the plug. It should back out OK. Before you install the new plug run a spark plug thread chaser into the hole to clean out the threads. (Advance,Auto-Zone, NAPA and others have them in the HELP or tool areas) Put a dollop of grease on the tool to catch anything that it dredges up.
Abby.Normal wrote:

--
Steve W.
Near Cooperstown, New York
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Thanks for the advice Steve. I've read about PB Blaster before on this newsgroup and it sounds like it might help. Although I don't know if I can effectively get in there to apply the heat - that #5 plug is in tight quarters. It angles forward, and is behind/ underneath the brake booster. I might bite the proverbial bullet and let a mechanic deal with this one if I can't get it out after one more attempt. I'm pretty sure I can physically remove it, I'm just psychologically afraid to try ;-)
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Unfortunately, this is a common problem, especially with aluminum heads. The problem you are facing is that very likely the threads are already destroyed. If they are, then the only recourse you have is to remove the head restore the threads with a helicoil and overhaul/rebuild the entire head. The large cost is the labor, whether you do it or a shop does this. Parts are cheap, labor is expensive. My advise, if you are a mechanic, is to remove the head as is, bring it to an automotive machine shop and have then check the valves, seats and guides. Replace or regrind as necessary, check the springs for set or cracking, reassemble with new seals. At the same time they will check the deck for straightness and retap or replace all sparkplug threads. This machine shop service is not expensive because they have all the tools and machines required. The whole head can be done within 3 hours, 4 hours tops if all actions must be taken. Very often, helicoiling a sparkplug thread can only be done from the combustion chamber side because of thread access limitations of the retapping tools or the coil staking tool. When reassembling the engine, always use antiseize on both the headbolts and sparkplugs, infact every bolt if threaded into aluminum. Steve

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I managed to remove the stuck plug this evening. A little heat, some penetrating oil, and working the plug out and back in a little and so on did the trick. The old plug came out with perfect threads and nothing "extra", thankfully!
However the misfire is still there with a new plug installed.
My next thought... if I have a dead cylinder, shouldn't I eventually start smelling raw gasoline vapor out the exhaust? I smell no gasoline whatsoever. The old plug came out bone dry by the way - not oily or sooty or anything like that.
I suspect I might have a dead fuel injector. I should be able to verify this by pulling a couple spark plugs, removing the ignition fuse, and cranking the engine over, right? (a good injector would result in gas squirting out the hole, whereas a dead #5 injector would result in nothing coming out - that's my theory)
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wrote: <snipage>

Probably not a good thing to have gasoline spraying out with flamability issues and Benzene and such. How about pulling a spark plug wire and see if it makes any difference in the smoothness of the engine? Or, drive around for awhile and pull the new plugs again and find out which one is totally clean.
FMB (North Mexico)
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how about pulling the connector off #5 and see if there is any change. If there is no change try swapping #5 with another injector and see if the problem follows the #5 injector.
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Physically swapping the injectors is almost next on my list of things to try. I did disconnect #5 injector at idle last night and found very little, if any, difference. I looked up the normal resistance of the fuel injectors, it's between 10-12 ohms - I will check that tonight (both the suspect one and the others on that side for comparison).
I also did listen to each injector with a dowel rod against my ear, and while there's a lot of cyclical noises going on, it does sound like #5 is "quieter" than #3 and #1. I remain hopeful though primarily because I perceive the lack of fuel odor to be a very good sign in terms of this being just a dead fuel injector instead of something along the lines of lost compression. I have not run a compression test (yet anyways).
Thanks for the help thus far!
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I was going to ask you if you had done a compression test yet but I see you stated you had not.
Swap injectors and see if the problem follows the injector. That would be a fairly simple test. You could also have a bad connection to the #5 injector.
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