Altima Misfire, Oil in Spark Plug Wells

"Urambo Tauro" (urambotauro) 08/24/2019 at 23:30 • Filed to: wrenching

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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.

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...

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...

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

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.

Full of the sound of the Gran Fury, signifying nothing. > Urambo Tauro 08/24/2019 at 23:45

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What do non-directional beacons have to do with an oil l leak? Is she a pilot? 

Urambo Tauro > Full of the sound of the Gran Fury, signifying nothing. 08/24/2019 at 23:51

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The beacons are lit! Oppo calls for aid!

( LOL, fixed. Thanks )

gmporschenut also a fan of hondas > Urambo Tauro 08/25/2019 at 00:34

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Can you look down to make sure it wasn’t some hacked threaded insert? https://www.parts.com/index.cfm?fuseaction=store.sectionDiagram&vehicleID=184891&diagram=F600225

Urambo Tauro > gmporschenut also a fan of hondas 08/25/2019 at 00:58

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Maybe it i s threaded? I dunno. I c an’t find any diagrams or anything to show for sure. And s he’s driving it again now, so I don’t have access to the vehicle. (S he’s prepared to pull the coils out and sop up excess oil every few days or as needed. A temporary PITA.)

In the meantime, I’m trying to plan ahead , so that the valve cover will only have to come off ONE more time, if possible. I did manage to find a forum post where someone says they removed one of the tubes for better access to repair the spark plug threads, but no further description or pics.

You’re probably right that they’re threaded, but I’d like to be sure before I go applying force.

gmporschenut also a fan of hondas > Urambo Tauro 08/25/2019 at 01:14

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I was thinking could the spark plug itself be leaking. But that would be unburnt fuel , not oil.

The v6 seems to have replacement tubes, but the 4 seems to have thrm as part of the cylinder head

Urambo Tauro > gmporschenut also a fan of hondas 08/25/2019 at 01:40

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Yeah when I searched for replacement tubes, just to see if that was even a thing on this engine, Google got my hopes up with   a few false leads to V6 parts .

But I’ve been reviewing the small handful of pics I took while the valve cover was off, and as near as I can figure, I think   the tubes ar e in fact separate pieces that are either screwed or pressed into the head . I may not be able to get new ones, but maybe I can reuse and resea l these .

merged-5876237249235911857-hrw8uc > Urambo Tauro 08/25/2019 at 08:19

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In the meantime, you can swap around coil 4 to a different cylinder to see if the misfire moves.  Just to see if the coil is the culprit.  Or just replace them all for good measure.   With that mileage, might as well.  

MM54 > Urambo Tauro 08/25/2019 at 09:23

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I don’t like throwing parts at a problem, but this is a case where it’s probably worth buying a set of spark plugs and planning to install them. If it still acts up, swap the #4 coil with one of the others - if the miss follows the coil, the coil needs replaced. If not, the coil is okay.

In any case the oil leak is worth looking in to, but unless you can prove that cleaning it out solves the miss I wouldn’t be too set on it being the cause.

(I don’t know anything about these engines but from your picture it looks like those tubes are pressed into the head)

coqui70 > Urambo Tauro 08/25/2019 at 10:48

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It may be seeping through the hole for the coil itself, sometimes the o-rings/seals get worn out . Had a ‘93 Civic where they were not screwed in, just popped into place. One coil would not seat properly.

Also if it has one check that the PVC valve is working properly - to much pressure inside the valve cover can also force seepage.

Urambo Tauro > coqui70 08/25/2019 at 11:04

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The coil boot isn’ t supposed to be making contact with oil at all. It’s not there to seal the spark plug against oil, but to keep dust out. That’s all.

I haven’t seen any service history on the car, so it may be time for a tune-up, including a PVC valve...

Urambo Tauro > MM54 08/25/2019 at 11:12

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Yeah it’s bugging me how the oil leak distracted us from digging any further. There’s a good chance that it’s due for plugs anyway. I forgot to mention that we did go ahead and swap coils #3 and #4, but we still didn’t do anything about the plugs. I hope the misfire pops back up before too much oil gets into t he wells again. There didn’t seem to be a whole lot of oil the second time around. Any oil is to o much , but I don’t think there was enough to case a misfire this time. But it’s gotta be done.

Urambo Tauro > merged-5876237249235911857-hrw8uc 08/25/2019 at 11:13

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I forgot to mention, we did swap coils #3 and #4. Cleared the code too. I’m crossing my fingers that the misfire will return before too much oil seeps back into the wells.

dcp > Urambo Tauro 08/27/2019 at 15:24

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That’s nuts. I had similar oil leakage on a VW 1.8T once it hit about 200k miles (LPT: the coil pack shouldn’t look like an oil dipstick when removed from its home atop the plug). No misfires, though. The old rubber valve cover gaskets had gotten right crispy, but swapping in a new set was straightforward and quick, sucked out the oil sitting on top of the plugs with a fluid extractor, cleaned the coils and plugs, and it’s been dry since.

But that notwithstanding, as you’re soliciting ideas and different perspectives, I figured I’d chime in. I’m certainly no expert, though, so take what I have to say with several large grains of salt.

I do think the misfire and oil leak are unrelated. It looks like that coil pack design has a rubber boot down near the spark plug, which would (hopefully) seal out any oil from contacting the coil-plug connection (not really any way to know for sure, since when you pull it out, the oil sitting above the boot would then get all over everything anyway). The coil pack design in my VW did not have such a boot , so oil came in contact with everything in the plug well. And even with the oil more than halfway up two of the coil pack “stems” (for lack of a better term), I never had a single misfire... as long as there is metal-to-metal contact between the coil and plug tip, I would think the path of least resistance for the electricity would still be through the plug and across the gap, instead of through the oil to the grounded cylinder head; my understanding is that oil in general is a decent insulator (it’s used in transformers as a coolant and insulator), and nowhere near as conductive as, say, water — though I’m sure its conductivity can vary somewhat depending on its makeup, additives, and whatever metal shavings, carbon, and other contaminants came from the engine. Still, the most probable way I can think that oil could cause a misfire like that would be if it somehow made its way into the electrical bits of the coil itself, but usually that bit is pretty well sealed off from the elements (barring some physical damage to the plastic casing).

In any case , I think your hunch of it either being a bad coil pack or poor wiring is more likely. Too bad the misfire is intermittent... I hate diagnosing those kinds of problems.

And you’re right, that oil leak should still be addressed. If it were me, I’d probably focus on that first — it’s at least consistent, and while I don’t think the oil is causing the misfire, it would be nice to just eliminate that possibility altogether. Super annoying that the plug tube seals are integrated into the cover. Reminds me of GM-era Saab and their all-in-one coil pack “cartridges.” And since they decided to go that route, why not integrate all the gaskets/seals into the cover, so you only have to buy/replace the cover alone? Insane. But I digress. I would be surprised if the oil is coming up from underneath... maybe if it was just one plug experiencing oil intrusion, but three? To me that would indicate a more widespread problem with the head/plug tube design, and given how long this engine has been in production, I expect you’d find at least some mention of it online.

Honestly, given the huge variation in quality, fit and finish of aftermarket car parts these days, I wouldn’t be surprised in the slightest if the plug tube seals they pressed in are the wrong size, or don’t seal to factory spec (unless you picked up an actual Nissan valve cover). The only other thing I can think of is maybe it wasn’t torqued down tight enough and/or in the right sequence... I did see that there’s a factory-specified order in which to tighten the cover bolts/nuts. That said, from the photos it doesn’t look like the tube seals are pressed in between two surfaces (rather, they appear to just seal around the plug tubes, sort of like o-rings?), so in that case, tightness would really only impact the perimeter seal. Hard to say.

Well, I got a bit carried away there. Sorry for the wall of text... but yeah, that’s my take on it all. Not sure if it helps, but it’s always nice to have different opinions when troubleshooting something baffling like this IMO . Hopefully you figure it out soon, and without spending too much more money !