So my sister got her hands on a 2005 Altima, with the 2.5L engine, which has recently developed a cylinder #4 misfire. Started poking around, and one of the first things we noticed was a bunch of oil in 3 out of the 4 the spark plug wells.

NBD, I thought. At over 200k, there’s some weepage around the outside of the valve cover too, so it’s time for some new seals anyway. Well, come to find out, those tube seals aren’t available separately because they’re permanently integrated into the plastic valve cover. The whole damn thing has to be replaced.

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So she got one, and I walked her through how to replace it. I’m pleased to report that the top end looked pretty clean underneath! Somebody’s been keeping up on oil changes. We cleaned the tubes out and wiped the coils off, and I sent her on her way. The misfire was gone! ...for about two weeks.

When she returned, cylinder #4 was the one misfiring again. Bad coil? Heck, we never even pulled the spark plugs, because we stopped trying to diagnose anything once we found the oil in the spark wells...

So we took the engine cover off again and pulled coil #4; lo and behold, it was wet with oil again! So were #1 and #3, although they weren’t yet experiencing misfires. I immediately started to suspect a defective valve cover, since it was replaced carefully, under my supervision. Everything had been cleaned and aligned properly, even put a couple dabs of RTV in the corners by the timing cover, as you do. But there were no signs of oil leaking past those upper tube seals. It seems that the oil intrusion must be coming from underneath...

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Alas, my google-fu is failing to find any further info. Valve cover replacements for this engine are so overwhelmingly common, that it’s all that comes up. I can’t find any information about the spark tubes. I don’t know if they’re machined/cast into the cylinder head, or are separate pieces. And even if they are separate pieces, I can’t find new seals for them anyway.

I fear that the next step may be to pull the valve cover back off, so that I can tug on the tubes to see if they feel loose at all. Heck, this might not even be the actual cause of the misfire. She might indeed have a bad coil, or need new spark plugs...

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Or maybe, just maybe, this T-splice I found in the wiring harness might end up being the culprit.

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Man, I hate finding stuff like that. Sure enough, that’s the one for cylinder #4. Makes me wonder who put that there, and why. Maybe somebody else was trying to track down a misfire, before my sister ever got the car.

The paint marks on the coils and their respective connectors indicates that none of the coils have ever been changed or swapped. It might be time for one or more coils after all. But something still needs to be done about that oil leak.