3 dirty intake runners?
 

I changed out to NGK iridium plugs today (coming from a Mustang, this car is a PITA to work on:shakes head:) and noticed something weird. Intake runners on 2, 4, and 6 were noticeably dirtier than the other 3. I know I could just get Kenchan to photoshop my pic and make everything ok again, but I'd still like to know the cause...

Aren't 3 of those for exhaust? If you mean the front intake is dirtier than the other two, I'd say that's normal. Possibly the EGR or some other pollution control that dumps toward the front of the engine.

:confused:

I highly doubt it since they go directly into the plastic intake plenum. Plus they're not nearly dirty enough for that... just oily.

I'm going to feel incredibly stupid if you're right though.:facepalm:

u still want me to photoshop? :icon17:

:wtf2:

It's probably just a characteristic of differences between the banks -- there's usually at least small differences in mixture/AFR correction due to sensor variation.

EGR valve location may enter into it as well as SouthArk suggested.

Overall, I'm guessing its normal.

I was looking at it cross-eyed. You are correct. :tiphat:

But there is sooooo much difference between the two banks. The slight differences in the even-numbered bank looks normal to me (recirc, &c). Even the "dirty" odd-numbered bank don't look all that bad (dirtier than what I'd like to see, but I've seen worse). The fact that the odd- and even-numbered runners are so different worries me.

But I've already proven that I'm no expert. ;)

Mine is similar, not sure which is more discolored though, it's been a while since I took the mani off

Yeah, that's what makes me nervous. If they were all clean or all semi-dirty I wouldn't have thought twice about it.

Can't hurt.:icon17:

The one and the only thing that travels through the lower intake manifold runners aside from intake air, is PCV system re-circulation.

Its just PCV oil not being evenly distributed. While it leaves a film on the runners, its effects to engine performance are negligible.

Thanks! I was concerned for a moment.:tiphat:

It's the same for mine and others if you do a search. Catch can is probably on my favorites now because 25 miles is still enough to leave oil residue.

Just for laughs I should go to the Nissan dealership just to find out how much $$ I saved myself by doing this...

I don't even want to know with mine. I changed the valve cover gaskets, spark plugs, cleaned throttles, replaced throttle and manifold gaskets, and I'm currently replacing the upper intake manifold with a brand new one. The old one warped enough to cause vacuum leak.

Are you getting a catch can setup? I recently installed it, and the intake manifold is bone dry. It's really nice.