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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Been meaning to look into this for years. The BBK TB swap reminded me. Why would there be one PCV off the drivers valve cover to the rear of the Plenum, but an unrestricted tube off the passenger valve cover straight to the TB? It makes for a Godawful mess in there. I've since installed a catch Can in between the passenger valve cover outlet and TB. I don't understand the logic of piping oil vapor into a throttle body. Unless I'm missing something, but my factory setup has an aluminum tube connected to that passenger cover and straight to the right side top of the TB
Not completely sure what you're asking... but the one tube that has the PCV valve in it, carries funky air contaminated with crankcase vapors up to the intake manifold to be sucked into the engine and burned; and the other one brings clean filtered air from somewhere (varies according to the specific intake system) into the crankcase to replace the air that's sucked out.
ALL cars with PCV work this way. It's not specific to TPI.
The line with no valve is the makeup air. It goes to a hole facing the front of the TB where it picks up air that's been through the MAF but hasn't made it to the throttles yet. That air is at atmospheric pressure (or very close to it). The line with the valve connects behind the throttles, therefore it has engine vacuum on it.
Keep in mind, with a MAF system, ANY AND ALL air that is ingested by the engine, NO MATTER how it got there, MUST pass through the MAF first, to be metered. Otherwise the ECM won't know that it's there, and therefore won't know to add fuel for it. The arrangement described above makes sure that the crankcase is merely a minor detour for some portion of the metered air on its way into the intake.
Can't speak to anything about "Godawful mess". It is what it is because that's what it has to be. Not really alot of choice in the matter.
Not completely sure what you're asking... but the one tube that has the PCV valve in it, carries funky air contaminated with crankcase vapors up to the intake manifold to be sucked into the engine and burned; and the other one brings clean filtered air from somewhere (varies according to the specific intake system) into the crankcase to replace the air that's sucked out.
ALL cars with PCV work this way. It's not specific to TPI.
The line with no valve is the makeup air. It goes to a hole facing the front of the TB where it picks up air that's been through the MAF but hasn't made it to the throttles yet. That air is at atmospheric pressure (or very close to it). The line with the valve connects behind the throttles, therefore it has engine vacuum on it.
Keep in mind, with a MAF system, ANY AND ALL air that is ingested by the engine, NO MATTER how it got there, MUST pass through the MAF first, to be metered. Otherwise the ECM won't know that it's there, and therefore won't know to add fuel for it. The arrangement described above makes sure that the crankcase is merely a minor detour for some portion of the metered air on its way into the intake.
Can't speak to anything about "Godawful mess". It is what it is because that's what it has to be. Not really alot of choice in the matter.
The tube I'm referring to is aluminum. Runs along the bottom of the passenger side runners, bolted to the intake manifold. It connects via a grommet to the top of the passenger side VC and is plummed into the throttle body through a port on the passenger side of the TB that brings it in behind that Blades. My PCV is as you mentioned, plummed into the plenum. Just struck me as odd to have an air source that's contaminated by oil plummed into a throttle body. It's still setup like that, just now it's going through a catch can to keep it cleaner.
The tube I'm referring to is aluminum. Runs along the bottom of the passenger side runners, bolted to the intake manifold. It connects via a grommet to the top of the passenger side VC and is plummed into the throttle body through a port on the passenger side of the TB that brings it in behind that Blades.
Sounds kinda like the fresh air "makeup" air supply. It goes a port in the front of the TB, in front of the throttle blades, to the pass side VC, to draw in the clean fresh filtered makeup air.
Wrong place to put a catch can. Those belong on the suction side of the system, in the line with the PCV valve. Where dirty air coming out of the crankcase is being sucked out. The purpose of a catch can is to reduce the amount of raw fluids (oil and water, mostly) being drawn into the intake. Not to somehow reduce the fluids in the clean fresh filtered air being drawn into the crankcase to replace the dirty contaminated air.
When the engine is @WOT the crankcase blowby air goes into the intake plenum AND into the throttle body too. The PCV is "open". vs its pindle valve p osition when at idle "closed" (its not actually sealed closed at idle.
If the engine has bliw by @WOT (poor ring seal) there will be some oil vapour going into both the PCV and the "make up air" side too. A oil vapour separator catch can helps. keep the engine injesting oil thru the pcv system.
EDGE, is this the god awful mess you refere to ?
I get this in my tb and the only place it seems it could come from is the ccv hose, I was considering a catch can there too. I think it's the reason why my throttle blades stick and give me a jerky acceleration when I touch the pedal.
Sounds kinda like the fresh air "makeup" air supply. It goes a port in the front of the TB, in front of the throttle blades, to the pass side VC, to draw in the clean fresh filtered makeup air.
I think I may be Daft. My Brain processes like an IBM 386 sometimes. That line I'm connected to is not a vacuum, that's a feed out to the VC isn't it? I have the flow backwards don't I. I was confused because there's a bit of oily residue around the blades. I figured it was coming from there. So I need to re-plumb that can to the PCV line itself. @F-BIRD'88 summed up what's happening at WOT "there will be some oil vapor going into both the PCV and the "make up air" side too." This is where I was confused I think. Been doing a lot of ECM tune runs and have been at WOT quite a bit.
EDGE, is this the god awful mess you refere to ?
I get this in my tb and the only place it seems it could come from is the ccv hose, I was considering a catch can there too. I think it's the reason why my throttle blades stick and give me a jerky acceleration when I touch the pedal.
I have a BBK so there's no cover to remove anymore. I don't get that waxy smutz so much as I do a bit of oily residue.
Just struck me as odd to have an air source that's contaminated by oil plummed into a throttle body.
That was necessary to comply with emission regulation. Otherwise, the blowby gas would be vented through the atmosphere. If you get excessive oil, maybe (just a maybe) you have excessive blowby gas.
At low engine operation, there is a vacuum applied on the PCV valve to restrict flow. The CV side will bring fresh air from the throttle body. At WOT, there is no vacuum and the PCV valve is fully opened letting blowby gas go through. At WOT, the CV side can also reverse and bring blowby gas. That's why you also get mess on the CV side.
Apparently, valve cover baffles can reduce the amount of oil that goes through.
If I said something wrong, @sofakingdom will correct me with his usual passion.
Last edited by SbFormula; Apr 4, 2023 at 07:19 PM.
That was necessary to comply with emission regulation. Otherwise, the blowby gas would be vented through the atmosphere. If you get excessive oil, maybe (just a maybe) you have excessive blowby gas.
At low engine operation, there is a vacuum applied on the PCV valve to restrict flow. The CV side will bring fresh air from the throttle body. At WOT, there is no vacuum and the PCV valve is fully opened letting blowby gas go through. At WOT, the CV side can also reverse and bring blowby gas. That's why you also get mess on the CV side.
Apparently, valve cover baffles can reduce the amount of oil that goes through.
If I said something wrong, @sofakingdom will correct me with his usual passion.
I believe you are correct. Once spirited driving begins the makeup air will reverse flow I believe. Therefore I'm putting in two catch cans. I don't get any more blowby than what's considered normal. But given that I have a new TB and heads, why not keep it clean? I do know that an oily mix in the air stream can knock down the octane level. Less than $100 for two cans. Cheap enough. May as well keep it as clean as possible.
Yes I have the same "cheapy" catch can in red instead of blue. Evil Energy Universal? They don't catch much IMO.
@SbFormula mine had about a thimbles worth of very clean oil in mine after about 30 mins of aggressive bursts with the car. Hope I'm not staring at a problem. No oil burning whatsoever. Oil level is perfect. Maybe the baffles aren't the greatest in these aftermarket valve covers. Never really paid attention to it before when the PCV was hooked up the regular way to the backside of the plenum.
You've got 1 PCV valve because that's enough air flow to sweep the crankcase for a typical street engine. If you have too much air flow then it starts to look like a manifold vacuum leak to the engine and all the problems that come with that. Hotter engines with more blow-by may need modified crankcase ventilation.
When you go full throttle there is enough piston ring blow-by that gases spew out of every orifice of the engine. Dirty side, clean side.... doesn't matter -- it's all "dirty" under WOT. That's why you're getting some oil residue at the throttle body.
If I said something wrong, @sofakingdom will correct me with his usual passion.
sofakingdom is one of my favorite characters of all time on any forum. Super smart, never wrong (literally never seen him be wrong), and hilariously insulting!
One of my favorite quotes of all time....
And throwing things at your food as it ran by so that it slowed down enough for you to take a bite worked for MILLIONS of years. Grocery stores have been around for... what... 150 years or something? Does your "argument" (since what you said is not logical, I'm using the word VERY loosely) mean we shouldn't buy food at grocery stores?
