I am removing the plastic intake plenum to replace the Left side fuel injectors because my LTFT bank 2 is going lean under load. No misfires, no codes. And i suspect the fuel injectors are faulty. If it was a vacuum leak, the LTFT would be less affected under load than at idle.

After removing the airbox, I can see heavy oil residue (not wet) on the aluminum intake, up the fuel injectors, mostly on the passengers side. Its not from the valve covers although I am changing the valve cover gaskets while I am this deep in. What I’m not sure of is if the oil is migrating up from the intake/head gasket or migrating down from the intake/plenum gasket. I started cleaning the oil off with carb cleaner before taking the picture but in this picture you can see a thick coat of oil and dirt at the front edge of the intake which is what the whole area looked like before cleaning. The oil is all the way from front to back.

So where would oil come from? Is this from leaking fuel injector seals, escaping pcv vapors, coming up from the block valley? Should I also replace the intake/head gasket? Would that do any good?

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Update. I just removed the plenum. The gasket was hard an compressed and soaked in oil. I’m shocked that there is so much oil in the lower intake runners. The original pcv valve was still in the truck (222k miles)and when I removed it, it was hardly moving. I replaced that last month. Hopefully that reduces oil consumption.

Here is a picture of the plenum seal and the oil which was outside the seal area.

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Now you have first hand knowledge why some of us think the 'oil catch can' is a good idea.

If your plenum seal had not dried up, that oil would just burn out the exhaust.
PCV vents into the intake, suprising the amount of oil you get in just 5k miles...with oil catch can. I have one and it traps oil.

Still considered snake oil by most.
Not needed, how could anyone do something better than Toyota corp... sarcasm
...these things go 200k plus with out a catch can...

Which reminds me I need to install one. Which one are you running?

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I had one on my TT corvette because it was boosted. I considered one on my kids RX300 lexus because the valve cover was poorly designed but by 2004 the 3rd iteration fixed the problem, so I replaced the valve cover. Heres the issue. There is a plate inside the valve cover to stop liquid oil from getting suck up. But the oil vapors carry a lot of oil and it has a large port on the front edge. It dosent give the liquid oil enough time to separate out before the pcv ingests it. I wonder if a newer engine has fixed the problem?

About the catch can. Id forget to empty it and end up pouring liquid oil into the intake.

From what I've seen, it only needs emptying every oil change or so.

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Cheapo ebay, ADD W1 knock-off $30. Had burs on the baffle drill holes, cleaned up with drill bit in hand... so little metal bits did'nt get sucked into intake. 1" of oil in a pint bottle (vodka) every oil change, 5k miles or so.

I just add it to my oil charge routine.

Probably overkill for most.
If you dont diy maintenance the can is probably a bad thing.
Doubt a lube shop would think to dump it.
...not saying you dont do maintenance, just a genneral observation for the normal folks that can just drive and not have some wierd desire to modify everything. Lol

I went way over kill on my 5th gen. The Moroso name adds 5 hp right?
It does a good job and adds a little bit of bling, but stupid expensive for what it is.

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Having seen the front suspension on your 4th gen, you have expensive taste!

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Which injectors did you buy? I'll be doing the same job soon and am trying to decide if buying from RockAuto is a good idea.

I bought GB reman injectors from rockauto.

Those were the ones I was looking at too. Well if you have any issues I would appreciate hearing about it.

Yea, my Son is grown, and I work on the road, so I have no regular commute to pay for. I also have no wife and no life, so I do tend to waste my money lol.