3RZ PCV Return fitting size, oily spark plug well

Hi all,

My 99 2.7L Tacoma recently returned from a 600 mile trip to Montana with no faults, but a few days after my return, the engine began to stutter under load - more than 1/4 throttle at under 2000 rpm would cause it to stutter, and it even backfired on me. No engine codes were being thrown.

I let my mechanic friend look at it, and he put a (timing light?) on all the cylinders, and found cylinder 4 to be misfiring like crazy. I pulled the Cyl 4 spark plug, and my socket came back oily as hell.

Here's where it gets a little weird. When I bought the truck, the previous owner had installed a PCV breather - just a tiny air filter connected to the PCV valve, and a rubber block-off on the PCV return on the intake manifold. I decided to do away with this setup, and installed a ghetto inline PCV catch can using a Husky air compressor inline filter. Something weird I ran into was that the fitting on the intake manifold (return) was WAY larger than the PCV valve. I disregarded it and just got adapters to fit onto the filter at the time (more than a year ago).

At this point, I'm thinking my ghetto modification has to go, and may be the cause of the spark plug well closest to the PCV valve being oily, and not the other plugs. I looked at a friend's 3RZ engine, and it looked like mine was ground and drilled out to fit the larger nipple.





It even looks like they ground out too much metal, and there's a tiny hole showing through...



Here is a comparison to the PCV valve. Much, much larger.

My questions are: Why would somebody enlarge this? Do I need to replace my head gasket/rebuild my engine?

Thanks all.

 

The picture you posted (and also confirmed when I looked at my friend's 2.7) shows the hose fitting installed into the cast aluminum of the intake manifold/throttle body, however, mine looks like somebody machined part of it off, and installed a hose fitting many sizes larger. I would connect a hose between the two, but a single size hose would literally not fit - I removed the PCV valve and held it up next to the other fitting for a size comparison in the last picture.

 

Regardless of the PCV hose sizes, oil in the spark plug well usually points to a valve cover gasket leak. Replacing it should be fairly cheap and easy to do yourself.

 

Thanks! So most likely not a head gasket, then? The electrode seemed a bit oily, but that might be from the oil dripping down when I removed it. I was also under the impression that if a gasket were to leak, it would usually be evident on all 4 cylinders...

I know which side of the PCV valve to place in the valve cover - the smaller end would just hang out loosely, the larger end is the one that has the tight fit. That being said, the large end is still much smaller than the return fitting on the intake manifold, and the small end is even MORE mismatched. The fitting on the manifold is for a 5/8" hose, and if I tried to put the small end into the valve cover, it would get blown off when I started the engine because it does not fit. Even with it in backwards, the PCV valve's fat end is still much smaller than the return hose, and also does not fit.

I KNOW it has been modified and enlarged, I just want to know WHY.

 

There doesnt have to be oil in all cylinders. In fact its typical for only one or two to have oil in them. The oil is highly conductive and shorts the spark to ground (the block).

 

There were 2 separate sizes of PCV fittings on the intake manifolds.
No shit, my dad has a 99 4Runner 3rz with that huge fitting and my 99 Tacoma 3rz has a smaller one.
I'm thinking there may have been a manifold swap at some point in time on your truck.

Also, there are donut shaped gaskets for the spark plug tubes that seal on the valve cover to keep oil from the valve train from getting in there. Most overlook these when opening up the VC, but they need to be replaced every time you open her up.

 

Thank you! I'm sure something like this happened...the rest of the intake system is pretty ghetto modified...the previous owner even installed a "TRD" throttle body spacer. Snake oil, much?

I did also notice a gap between the valve cover and the spark plug tubes, and it really seemed like there should have been something there to separate the two sections of the engine.

Thanks for your help TW, you're awesome!

 

Yes, actually.
My dads 4Runner with the larger fitting is California emissions. My Tacoma with the smaller fitting is Federal emissions.

 

Didn't check that.
I only pulled the hose off of the manifold fitting so I could get at the TPS.

 

The oil leak is the round grommets in each plug hole leaking, you should change all 4 and the valve cover gasket at the same time, normally it all comes in a kit, but make sure they do..

And yeah, your trying to put the PCV in the wrong side, it goes into the valve cover rear hole...