Found cause of 380SE miss, but what does it mean?

So I went and pulled all the spark plugs. They were all pretty good except for cylinder 8. That one was fairly gunked for a regular change interval, but extremely gunked considering it only has 4000 miles on it.
Thanks, Richard
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be sure sparkplug and or sparkwire are good
...not fairly new...but working...fairly new does NOT always equal working
actually you haven't found the cause...you have found the effect. the effect of missfire on No 8 it causing what you found good luck with the cause
alex

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Is there any way for me to check this without replacing it? Buying another spark plug is not a big deal, but buying a new wire is a waste of a lot of money if I don't need it. Also, considering that the plugs only have 4000 miles on them, can I just change the one that was fouled? Thanks, Richard

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If it is oil deposits on the plug, it may have a valve guide "floating" at that cylinder, i.e. no longer attached to the head. This can be fatal. Do not drive the car until someone pulls the left cam cover, sets no. 8 to top dead center with the valves closed, pressurizes no. 8 to hold up the valves, and removes both valve springs and seals from the guides for no. 8. With the air OFF, check for excessive side play between valve and guide, and evidence that the guide itself has been moving up and down in the head.
Bill Ditmire Ditmire Motorworks,Inc. 425 White Horse Pike Absecon,NJ 08201 http://www.ditmire.com 609-641-3392
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If the car has gone about 1000 miles with the miss and not died yet, could this still be the issue? How soon can it kill? My dad says he only needs about 1 more year out of the car or so (then it won't be junked, but we can just park it. Once I'm out of college I'll be able to do all the things I've planned on doing to it)

What do you think having someone do that cost me? Thanks, Richard
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You mean, like, see no evil, hear no evil...
The fouled plug is the handwriting on the wall. Doing something about it now may prevent a failure, or it may be too late already. If the guide is still secure on the head, and is just passing too much oil down the valve, replace the seals for those two valves (better yet all valves) and change the plug as needed.
Bill Ditmire Ditmire Motorworks,Inc. 425 White Horse Pike Absecon,NJ 08201 http://www.ditmire.com 609-641-3392
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Pretty much. My family needs 3 cars, and the only reason the 380 hasn't been replaced is because I want it. He only needs one more year from it because he's waiting for the new vette, the new mustang, and to see what happens with the GTO. As far as the number of miles post-miss, I need to correct myself. It's been about 300-400 miles (i wasn't here when it started, and I just figured by how long its been going on that it had been 1000 miles, but it has actually been 3 or 400)

Is this something I can check? I can do pretty much anything on the car, I just am not good at diagnosing things from symptoms, and I don't have testing tools.

Is this something I could do myself? On a scale of 1-10, with 1 being changing the oil changing fuel injectors being a 4 and changing the rear main seal being a 10, what would this be? How much would this cost at $75/labor hour?
Also, that test you said to have somebody do before driving it any more, if I wanted to ask a shop how much they would charge to do it, what do I ask for (i.e. what is that procedure called)? How much you think they would charge to check it? Thanks a lot, Richard
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The cause of the problem turned out not to be a real biggy. The lamba needed to be adjusted (the little tool he used gave a reading of 2.5 and he adjusted it to 1.5) and the cylinder 8 fuel injector gets clogged up by something in the lines. The mechanic told me to flush it out and use some Techron. Richard

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I found why my 6.9 was running rough too, when I changed the plugs they all smelled strongly of fuel, so I immediately pulled off the distributor cap, and discovered the real problem - the contact on the rotor had fallen off - its never been changed in its life. replaced it, now the engine even starts on the FIRST rotation of cranking every time, basically 0.5 seconds after turning the key to start :)

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