Hey guys, I'm beginning the process of doing what I thought would be preventative maintenance as well as fixing some known problems. I know the valve cover spark plug gaskets are leaking, in particular cylinder #6. I have new valve covers, gaskets and spark plugs in the mail now and figured i'd get a head start and remove the plenum tonight. I was surprised to see the amount of oil residue on the interior of the plenum as well as a good amount of oil pooled up under the manifold gasket. I was planning on sanding down the casting marks as well as cleaning up the plenum and throttle body anyways I am just curious if this could be a bigger problem than just the valve cover spark plug gaskets. Any input is really appreciated.


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That looks like a lot.

 

That is way to much oil in your plenum....^....apparently you're having major issues! What you're seeing is "Excessive Blow By." How much oil do you go thru between changes? Have you checked your PVC valve, is it plugged? Might be the cause! Once it's fixed, get a catch can so you don't have oil running thru your valves.
Gary

 

I'll make sure to check the PCV valve after work tomorrow, I usually go through about 2 quarts of oil every 3k. In November I waited until about 3500 miles to change the oil which is rare and could hear the valve lifters clicking which scared me but I knew i was going to be putting the car away for the winter so I did not do anything about it.
Also just because I am not sure if this could cause/ compound the problem, I put a dynotune 75 shot in over the summer and went through two 10 pound tanks in about a three month period. I never had any weird smells/sounds when using the nitrous and the car seems to be running as good as it ever has and it has been in my family since it was new.

 

So the PCV valve was blocked and the hose that leads to it was surprisingly hard compared to the other rubber hoses in the engine bay I'm not sure if that is normal. I have not bothered to re install anything yet because my new valve covers will not be in until Wednesday of this week and I just want to be sure there is not anything else (like the PCV Valve) that should be preventatively replaced.
Thanks again for the input here everyone I really appreciate the help.

 

Had the same issu, hose was so hard it cracked pulling it off..pcv was jacked, got new one..still need to replace valve covers

 

How many miles is that, its a common site since the PCV valve gets oil vapor back into the plenum.

Just clean it up, replace the PCV its cheap and change the hose if you want.

If you really care get a catch can

 

Its at 142k and this all started because I was replacing the valve covers due to the spark plug seals. I am just trying to address as many issues as possible while the car is in pieces. I bought a new PCV valve and will be installing it when my valve covers come in. I notices a couple cracks in the radiator hoses and bought the Z1 master hose kit which I am pretty sure replaces all of the oem rubber hoses including the PCV hoses.

I have cleaned and removed most of the casting marks on the plenum and am debating on brining it to a friend today and milling the air horns down a bit with some professional supervision of course.

The problem I am hoping to solve today is if it is worth removing the lower manifold (not sure if this is the proper name) where the fuel injectors are located because there is even more oil built up in cylinders 5 and 6 than what was seen on the plenum. I am afraid to remove the injectors because I am assuming the fuel rail is filled with fuel and under pressure and I have never done this before. Is there anything special that needs to be done in order to do this or do you just remove the wiring harness and then the metal clip that attaches the rail to the injectors so the rail can be moved out of the way and then the manifold can be taken off.. with the injectors still installed??I cannot find DIY to walk me through the process.

Lastly, if I am at the mileage to replace the injectors I would consider replacing all six just to avoid me doing all of this work, getting the car back up and running only to have an injector fail in the next few thousand miles. I know there is no way to predict if and when this will happen and that I am on the forefront of the high mileage G35s so experience is limited but as always any advice or prior experience with this is really appreciated.

 

142k? And its probably never been cleaned, its absolutely fine nothing wrong with your car.

I don't have much experience either with higher mileage G35s, but it cant hurt to clean stuff and do preventative maintenance.

For Fuel Pressure, something on the lines of unplugging the fuse for the pump and try cranking it until it stalls. But look into that just search around here I am sure that info is here.

 

I doubt it was ever actually cleaned, I paid someone to clean the plenum and throttle body when I had the spacer and headers put in a few years ago but I would never know if they actually cleaned anything.
I really do not want to remove the fuel rails but the lower manifold is just covered in oil and I feel like it would be stupid to clean the plenum and not address the visible oil that is there.

I am about to move from Massachusetts to Florida and just want to be sure the car will make the drive without any problems as well as continue to be a reliable daily driver.

 

Yea the plenum was never cleaned from the looks of it. Oil coating the runners isn't going to cause any reliability issues. If its too much issue Id just leave it alone.

Dont forget you should also change the gaskets if you are going to take the lower apart.

 

Soo I got the runnners off, not sure if I damaged a fuel injector in the process..?

And every gasket I have taken off is going to be replaced with a new oem one.

 

Man you guys are scaring me.

 

When I installed my MREV2 & spacer I noticed oil in my lower plenum as well. 2006 with 49k at the time. Not as much as in your pic, but oil none the less. I researched and came to the conclusion the PCV system was the culprit. I installed a non-vented oil catch can with baffles in line between the PCV valve and lower plenum intake port. The catch can cought roughly about 2-3 tablesppons after 7k. Will see what it looks like when I tear into her hear pretty soon as I will be installing larger injectors for my build. Luckily I do not have any OC issues as many others have with the revup. Just figured I'd share.

 

Every car i've ever worked on has had oil in the plenum. That doesn't look too bad if that's 150K miles worth. The cars that had major issues had actual oil pooling or a black sludge.

If you are really worried, a oil separator might be a good idea...especially if you notice you are losing some oil between changes.


BTW...for the injector, some autoparts stores sell injector rebuild kits which include new O-rings and pintle caps. I know they have them for domestic cars as I buy them frequently for my Mustang builds, but unsure if they would have them for the G35. Considering the 3.5L is in a lot of nissans...it's worth a shot.