CA breather system discussion
Hi, Now that I have your attention:
After reading Bluey's running lean issues having the same myself, I found it was a disconnected breather hose on the left rocker cover.
The problem begins here. . .
Since I did this:
She's running rich so rich my AEM just sits at 10.0.
Help me solve this jigsaw please.
Last edited by Chriscooke; 01-03-2012 at 20:53.
Isnt the whole point of a catch can so the pipe doesnt go back into the intake until its passed through the can. does it run right? Surely the pipe from the plenum to the catch can to the intake is like a big boost leak.
Dear lord have mercy
As above really
There are different ways to setup the breather system that will divide opinion, but here is mine, but bear in mind I don't know CA's but shouldn't make much difference. I also have to assume a couple of things, 1. you do not have a one way valve 2. You have a pipe going from bottom end to rear top hidden in the pic.
1st of all if the plenum doesn't have a one way valve then when coming on boost insted of the air entering the combustion chamber mixing with fuel it is being pumped into the crank case (bad!), head (bad!), partly sucked back though by the turbo () and then leftovers tickling the AFM's nuts sack on it's way back out the air filter which I imagine would actually be a shit load of left overs. Well, that's how I see it anyway.
Here is a suggestion, block the plenum side of catch tank to plenum, it normally sucks air when on vacuum/no boost then a 1 way valve blocks that pipe when boost comes in to stop the above happen, the 1 way valves are often faulty anyway and leak a little, well mine was on a x reg.
Next on the back of the head have a nice straight pipe from head to bottom end, im guessing this pipe is hidden in the pic. You do not want positive pressure at the bottom end, this will allow it to pass into the head.
Next link the 2 front (rad side) together so both can breath and have them going to one of the catch tank ports.
Other catch tank port goes to the inlet trunk near the turbo (or vent it to atmos like I have done).
Does that make sense?
If you want catch tank setup not venting to atmosphere, you need 2 catch tanks.
Your setup would work on an NA engine, but this is a turbo engine, meaning pressure can be positive at the intake manifold. So there are valve to allow 2 paths of venting.
1/off boost, the intake mani valve is open, and cam covers are vacuumed by the intake mani.
2/on boost, the intake mani valve is closed, and the cam covers are vacuumed by the air intake before the turbo.
So if you want a real recirculating system, you need a catch tank on both routes. That would be MOT compliant (and fire hazard free, oil vapors can burn).
I also hope your sump breather is connected to a valve cover ... not very good routing though, it may have higher pressure in sump than in left(on the picture) rocker cover, and again more pressure in the left than in the right rocker cover.
Do This
PCV valve blocked
Intake trunk blocked
Pipe connects two cam covers.
Pipe go's to can.
This is the simplest way to go, and it works well. You can also replace the catch can by a beer can to spare some bucks. Or a milk bottle if you dont drink alcohol.
Um, excuse my ignorance but isn't the above a sealed system therefore pressuring the top and bottom?
Unless the catch can/ bottle is vented?
The catch can is vented
All breathers must vent somewhere, otherwise you'll pop the engine.
The catch can is vented in the OPs set up in exactly the same way as the stock system is. But with one thing missing it seems.
The ONLY difference in the system above is that it has a can to catch the oil droplets rather than them entering the front of the turbo like they normally do when the cars on boost.
What does appear to be missing is a one way valve on the turbo inlet. This would mean that on vacuum the vapour would enter the plenum as the standard car does. The other one way valve closes on vac and stops the engine from sucking extra air from after the AFM which may make it think the engine is consuming more air and cause it to add fuel to suit. Which would answer your running rich problem. Although as yours is exactly the same as stock there is no way it should make it run too rich so I'd be checking things like cam timing etc.
What people forget is that all these cheap catch cans are completely worthless unless they have a mesh inside to separate the air from the oil.
Nearly all catch cans are just an open pot with a filter on top which effectively works exactly the same as having a large bore pipe at the end of your pipe work. So in this system you may as well not even bother having that can in the pipe as its not catching even half of the oil passing back into the inlet.
The only way the cheap catch cans are ok to use is if they are at the end of the pipe with a filter on them. That way although most of the oil will still pass out the top at least the filter will stop the majority of it. And nothing is plumbed back into the inlet so it doesn't cause the lean running caused with oil vapour.
Last edited by m.d.; 23-02-2012 at 09:42.
Errrm. No.Originally Posted by jon200
The PCV valve at the end of the plenum is a one way valve.
The PCV valve allows air to be drawn in to the plenum when under vacuum (ie. off boost or on the over-run) from under the cam covers. This de-pressurises the cam covers and cleans out any oil vapour laden / blow by contaminated air inside them, replacing it with clean fresh air drawn from the elephant's trunk.
The PCV valve then closes under positive boost pressure, precisely to prevent any boost being lost or pressurisation of the air inside the cam covers.
When the PCV is closed the air under the cam covers is instead sucked out through the pipe connecting the exhaust cam cover to the turbo air inlet pipe, aka the elephant’s trunk. Either way the dirty air gets drawn into the engine and burnt.
The combined purpose of the OEM system is to make sure that the upper end of the engine does not become pressurised and to burn any oil contaminated / blow by gasses by passing them through the combustion chambers by either route. Burning those oil contaminated vapours helped the car meet anti-pollution regulations.
It is not however a terribly good thing for a modified turbo charged engine. Oil contamination of the intake charge increases the risk of det + creates exhaust smoke. That is where catch cans and one way valve modifications come in.
HOWEVER before adding catch cans etc Note that the OEM set up is a system entirely venting through the combustion chambers (it is NOT a sealed system). All air being combusted has passed through and been measured by the AFM. The ECU adds petrol based on that measurement. No unmeasured air can be drawn in. Unmeasured air getting in means that the ECU adds too little fuel. Too little fuel = running lean. And bang.
Bear this carefully in mind before adding open ended catch tanks etc to the breathers. You don’t want unmeasured air getting in any more than you want a boost leak. In fact less.
The OP's set up is effectively the OEM setup + a catchcan added into the pipe from exhaust cam cover to PCV valve. It can't cause any boost leak if the PCV valve is working properly.
What it will usefully do is clean a little of the oil vapour out of the air drawn into the plenum via the PCV valve on overrun. Not a bad thing. Where det is concerned every little more than helps.
What the OP's setup does not prevent is oil vapour being drawn into the elephant's trunk / inlet on boost. While this is the OEM setup and intention it is still dirty oily air, increasing the risk of det and a bad thing.
That's where the first / original one way valve mod comes in.
A one way valve inserted in the pipe from exhaust cam cover to elephant's trunk allows clean measured air to be drawn in through the cam covers and PCV when off boost, as per OEM set up, but then prevents oily vapour laden air being sent back in through the elephant's trunk, turbo and intercooler when on boost. Reducing smoke.
The fact that the air under the cam covers isn’t then scavenged on boost doesn’t seem to cause any problems. In normal driving prolonged periods of high boost are rare and alternate with substantial periods off boost when the PCV valve does all the scavenging / pressure relieving needed.
However, if concerned about it - and for motorsport / constant high boost situations it is probably a good idea to be concerned - venting the cam covers to atmosphere via a further one way valve + catch can to keep it all clean under the bonnet seems to do the job. Using a one way valve prevents unmetered air getting in. While this does let a wee bit of metered air escape the system it is unlikely to have any significant effect on air fuel ratios. If it does have any effect it will be in favour of a slightly richer and safer mixture, not a lean and more det prone mixture.
Certainly does for me, though I haven't bothered with a catch can - just run it down into the front chassis member under where the hot start solenoid used to be - where a little oil never went amiss holding the rust at bay. Tho in fact my engine doesn't actually vent any significant quantity of oil vapour at all. And if it did then I'd be more worried about the piston rings and valves than the breathers.....
Last edited by Rochester; 21-02-2012 at 14:30.
Easy way to cure all this is literally to just remove the breather to the manifold and the one to the elephant trunk. And just plumb them into the catch can but you need to have a third outlet for a filter.
I really wouldn't do that.
PCV valve left open to atmosphere is going to be breathing in unmetered air at all times plenum is off boost.
Plumbing the rest to a catch can is all very well, but not if it allows a reverse flow of unmetered air back in to the engine either.
Both ways you are going to be running unmetered air, insufficient petrol injected by the ECU and lean. A very quick way to say goodbye to your engine.
If disconnected PCV valve needs to be blanked off.
All other feeds to a catch tank need to have a one way valve.
ie. as R3k1355 said:
with the minor but important addition of a one way valve in the pipe to the can.
The disadvantage of that very simple set up is that there is no scavenging of the air and blow by gasses inside the cam covers, which there is if the PCV valve and air intake connection (+ OWV) are kept connected.
Last edited by Rochester; 21-02-2012 at 17:49.
I couldn't see the one way valve bud.
It's all part and parcel of the PCV valve internals.
To be honest I don't think there is anything else too it BUT being a one way valve ! Though I have never disassembled one to have a look.
I kinda thought it was common sense which is why I didn't mention blocking the PCV valve. But yes your right leaving it to atmosphere is not a good idea.
Blocking the manifold valve and the elephant trunk need doing to just run the two breathers to a vented catch can. No one way valves are needed for this method.
My personal set up involved just plumbing both breathers back into the inlet pipe but I had no AFM to confuse or damage with oil vapour. I had it like this for 3 years and it never had any issues. I kept an eye on the AFR though with a wideband and was perfect even at 2 bar boost.
For the SR I've fitted I'll be leaving one to the PCV valve and the other to a catch can with a one way valve and vented back to the elephant pipe.
Last edited by m.d.; 21-02-2012 at 19:09.
Would installing a OWV aid in scavenging or would it just get clogged. (does the valve type affect this?)
It won't. Oil vapour being drawn back in to the elephant's trunk, whether on boost or not, is downstream of the AFM, straight into the turbo compressor wheel. It doesn't matter whether the engine is on boost or off boost, oil vapour can never back up into the AFM to contaminate or confuse it.
The AFM measures the amount of air that has gone through it, then tells the ECU. The ECU adds enough petrol via the injectors to match that amount of air. If you have a boost leak and lose measured air then you end up adding too much petrol and running rich. Which may bugger up your fuel economy, but is very unlikely to damage the engine.
If you have extra un-measured air getting in to the system after the AFM (the opposite of a boost leak) then the ECU doesn't know about it, doesn't put enough petrol in to match it, and you end up running lean. And bang.
Last edited by Rochester; 21-02-2012 at 21:52.
Omfg Im confused. Would I be retarded in asking why there is a lot of trouble going into this?
I was under the impression Catch cans were slightly gimmicky and served no real purpose?
Thanks..
Sorry if its OT.
It's the system I run and it has no problems. The OWV simply stops unmetered air getting in by the back door and causing lean running. It doesn't aid in scavenging as there is no scavenging with your set up. Scavenging requires either a positive and hefty suck of gas from the PCV valve into the plenum or a hefty suck from the head into the elephant's trunk. Your set up eliminates both.
However it does allow any excess pressurisation build up to escape through the cam covers to atmosphere / catch can. On the negative side it does allow all those nasty oily vapours and blow by acids and gasses to sit in the cam covers and deposit as sludge.
I use two OWV's from Nissan Brake Servos salvaged from breakers yards (one in the elephant's trunk to cam cover pipe, one in the outlet from cams to atmosphere) plus of course the third in the PCV. They haven't missed a beat and show no propensity to get clogged. Why should they with nice lubricating oily air blowing through them ?
If your engine is running clean then there is no reason for there to be any heavy breathing anyway. The rise and fall of the pistons should balance each other, both above and below the head and in the crankcase.
If you get any pumping up and pressure imbalance above and below the pistons then you have some other problem causing it. Piston rings, burggered valves, blocked breather from under the oil filter cooler (the usual suspect) or whatever.
The top breathers ain't the cause of that one (unless misconceivedly misrouted), but a useful warning indicator if your catch can starts filling up with oil....
Last edited by Rochester; 22-02-2012 at 01:22.
Not retarded at all. Blocked / mis-routed breathers and / or misconceived re-arrangements of breathers without one way valves in the right place seem to be the main likely cause for the death of most CA18DET engines.
Understanding how the OEM system works, and why, is the reason I posted at such length above. And believe me, that summary is the result of years of reading posts, the manual, considering the piping and making mistakes before I understood it and got it (I think) right....
Once you understand what the OEM system does and how and why then you have a better chance of modifying / simplifying your system to work without ending up pressurising your block and buggering the oil flow to your bearings.... or running lean and bang... or neglecting your engine block to head breather pipe of the many 90 degree bends... etc. etc.
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