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.

I never knew it was even a thing. Which one are you running? Is this a good one?

Nissan 370Z Mishimoto Oil Catch Can

hmmm want to see more of the catch can thing hahaha!! maybe i can buy one too...:stirthepot:

Warped upper manifold Digi?? Is that what was causing your power loss issues?

Damn man, i hope you have finally sorted it out.

When i fitted my Motordyne manifold for testing, i dont recall noticing any variation in the soiling of the lower manifold. VQ37 has no EGR valve. All the EGR functions are performed via VVT (valve overlap). It shouldn't be exhaust soot because that would indicate a backfire through the intake.

I've never dissected an upper manifold before but i did stick a flashlight into it and have a look around. From what i remember, there are two inlets for the crankcase ventilation for a reason (i suspect there is a partition inside the manifold which separates the crankcase fumes from each bank) & that might have something to do with why one bank is soiled much more than the other. My car had approx 60,000km when i did the manifold swap and the lower manifold looked as 'clean' as your 'cleaner' bank. Like you, i was also very (pleasantly) surprised.

In summary, i'd check both your PCV lines and clean out the upper manifold with a generous amount of brake cleaner or a commercial parts washing machine then dry thoroughly.

You looks ok to me, I've had mine apart like 5 times swapping things for testing LOL

The one on the lft is the one off the car

Sorry guys... been pretty busy. Got in a wreck a few days ago (RIP '99 Accord sedan), so I've been busy sorting that out and found a new daily driver in the process as well.

The catch cans are generic ones I got from Amazon for about $20 each, and I modified them by adding a longer perforated tube on one side of the can.
http://www.amazon.com/Godspeed-Unive.../dp/B00400XFQ2

As for the warped intake manifold, it turns out the old bolts were "stretched" over time by a few millimeters. Nissan revised the part and installation excluding the additional metal spacer in the sockets and resorted to shorter bolts. I got done installing the new intake manifold, but I'm still having some minor vacuum leak issues. I don't have an accurate torque wrench, and I don't want to risk snapping another bolt. So I'm going to take it to a shop to double check it with an inch-lb torque wrench, if possible. After that I'm pretty much giving up, but the car is running fine. More details and photos on my thread once I get everything done later this week.

Still gross haha. Here's 1000 miles...

While a new engine might not see issues with power, I've seen some pretty disgusting looking motors over time as this stuff builds and builds on the mani, heads, valves, pistons etc. I want to keep it clean but that's just me.

At 60k miles, my valves are very clean with no carbon build up. The oil collects in the upper intake manifold and PCV hoses, and it clogs up the PCV valves. It's definitely really gross when it drips all over the place when removing the intake manifold.