quicksilver97ta

I'm trying to locate the source of an oil consuption problem. Heads and valves are freshly redone by a reputable shop and the short block only has 59K on it and NO history of oil consuption. I just replaced the PCV valve which didn't help.
So what is with the top plate on the throttle body? It has a line that feed to the valve cover so there is a source for the oil. I removed the plate and the gasket is in bad shape (torn, distorted). What is the purpose of this chamber? I think there is access there to the idle air circuit. 1+1=2, so is this feeding oil into the iac of the throttle body? It was oily in there but the oil is still very clean. The oil smoke out of the exhaust is actually most noticable at idle and start up, but hardly at all at part throttle. I have never read about anyone with this problem though. Any ideas?

grygst76

If you have oil smoke at startup coming threw the exhaust, you more then likely have to replace the valve seals. depending on your mileage they are worn out or not on the top of the guide anymore. It can be done with heads still on the car although IMO it's easier to replace them with the heads off.

Dave Feerst

that is the suction side of the pcv system.

quicksilver97ta

The pcv has its own vacuum plug in the intake just below the throttle body and the pcv valve is on the drivers side of the intake.
I'm not sure what that other line on the passenger side is for. This is what I'm asking, what is that whole "circuit" for? There was a significant amount of oil above the t.b. however, when I remove the oil filler cap there is NO blow-by.

I have wondered about the seals possibly moving up the stem and off the top of the guide but has anyone actually ever seen this on new seals?

predator

it is the clean air side it lets filtered air go into the crankcase to equalize the pressure that the pcv is taking out

quicksilver97ta

Ahh, I see. So maybe if something was not right, like that gasket, the IAC circuit could pull oil from the valve cover that way. There was oil in there, a small amount, that should not be possible if the air flow is from the t.b. to the v.c.

predator

i think so yes at idle probably

quicksilver97ta

Alright I'm going to go get a new gasket at lunch. I'll let you know what happens. Thanks for the replys.

ryaskovic

The line from the TB to the passenger side VC provides filtered, MAF- metered air to the crankcase, replacing the air that's been sucked out on the driver side, through the PCV valve.

Sometimes, especially on higher mileage engines, oil can make its way up this hose and into the TB. Note that this passage is not connected to the IAC air passages, but a passage in front of the TB plates.

Anyway, I modified mine with the filter described below, and all is well:

http://collop.cz28.com/custom2.html

Hope this helps,
Rob
95Z28

Injuneer

As pointed out, the NORMAL function of the line from the TB to the passenger side valve cover is to supply filtered, MAF metered air to the crankcase, so the PCV system can pull it out. But, the system is also designd to relive crankcase pressure and prevent it from building up. If your PCV valve is plugged, or you are getting excessive combustion gasses blowing by the piston rings, the crankcase will vent through that line back to the TB. That's when it picks up oil droplets under the valve cover, and carries them back to the TB, it builds up under the top cover, and eventually gets pulled from the port on the front of the TB, and into the intake manifold.

First check your PCV valve. If its OK, check for blowby. With the engine idling, take the oil fill cap off and feel and listen for any air "chuffing" out of the fill pipe. That would indicate blowby.

quicksilver97ta

Wow, thanks again for the replys, and thanks Rob for the guide, I'm gonna to pick that up this evening. I just picked up a new gasket for the top of the throttle body as well.
So that t.b. gasket is not as special as it looks? If I understand correctly, so long as it seals the top of the throttle body its "ok", no other "passages" to be concerned about? It was not only torn it was collapsing in the middle and not holding its form.

BLUETOPTA

This sounds like an interesting topic. is anyone else runing this Deutsch BF412 filter on the pass. side like that?

ryaskovic

I got tired of messing with the gasket so I just use a small line of RTV now. Working fine!

Rob
95Z28

quicksilver97ta

No luck. I replaced the gasket and removed the entire t.b. for cleaning. I also installed the BF142 filter mod. The intake was very dirty and I had cleaned it thoroughly upon installation. The entire plenum was oily dirty, it melted away easily with B12 as I sprayed inside.
After I put it back together I only had time to check the top of the t.b. where the line from the pass side v.c. is and there was NO oil in there. So back to inspecting the PCV circuit after work today. I'll pull off the entire t.b. as well and have a look again. :blah:

Dave Feerst

I had the same probslem with one of my old engines. I even put a breather on there inted of hooking it up to ported vacuum on the throttle body and I was still sucking oil up into the manifold somehow. I couldnt figure it out, so I opted to get LT-4 heads /intake,.