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Im experiencing some very confusing issues after changing my breather set up.
The car will idle (in closed loop) but bounces around from as low as 500- 1300rpm with AFRs going from 11 all the way to 19ish.
This ONLY happens when the recirculate hose is connected to the intake pipe.
If i take the hose off the intake pipe barb it will idle normal again (plugging the barb with my finger) If i VTA the CC hose it also idles fine.
I have a PCV delete, and 2 ports from the valve cover going to a catch can and then routed back to the intake pipe after the MAF.
I am very confused as to why it is all of a sudden doing this as I had the exact same system except each valve cover port had its own can (due to space). So the fundamentals of the system have not changed.
Any input will be greatly appreciated.
If it matters, 8MR, GSC S1s, Short ICP, Stock turbo, tuned on 98 octane
Are you running the oem MAF or are you tuned with Speed Density ?
I’m assuming your still running the MAF. If so, then what ever your changing to as a setup is resulting in pulling in unmetered air after the MAF which may cause the rpm and AFR issue.
Long ago before Tephra V7 came out I was running the MAF and had vented the PCV to Atmosphere at the same time the diverter valve was set to not recirculate. My car ran fine without any issues because I did not introduce unmetered air after the MAF.
The OEM setup is designed that the air introduced under the valve cover is metered. (Air is passed through the maf, then to the turbo, to the intercooler and piping, into the intake manifold and finally it went under the valve cover) Now you disconnected the intake manifold from the valve cover but rather capped the intake manifold and put a breather on the intake manifold. If you connect the other side of the valve cover back to the intake pipe after the MAF, the vacuum in the intake will be drawing in air from atmosphere from that breather where the intake manifold once was connected to. This air is after the MAF so your ECU does not know about the extra air coming in and tries to figure things out for a happy equilibrium by adjusting a/f ratio and idle etc..
So to be a bit clearer with the previous set up and the now problematic setup.
Previous Set up - No Issues at all
Valve cover PCV has been deleted and plugged (plugged at VC and Intake Manifold barb)
Valve cover has 2 ports each connected to a 1 in 1 out catch can (2 catch cans)
Both Catch cans are then connected to the intake pipe after the MAF to separate barbs
New Set up - Issues
Valve cover PCV has been deleted and plugged (plugged at VC and Intake Manifold barb)
Valve cover has 2 ports connected to a 2 in 2 out catch can.
Both Outlets of Catch can are then connected to the intake pipe after the MAF to separate barbs
To me this set up is exactly the same which is why i'm confused.
If i remove the catch can recirculate hoses from the intake pipe and let them just VTA and plug the intake pipe the car idles fine, put them back instantly results in the issues.
The hose that goes to the intake is "post" MAF and is sucking air from the valve cover or can.
Any air that is introduced after the MAF is unmetered air and will only be SEEN by the oxygen sensor which will then start dumping fuel to combat the EXTRA air.
Post pics of set up.
Hi everyone thanks for your input. I have uploaded some diagrams of the set up. Hopfully this clears it up. For reference the new catch can is the Vibrant Closed Loop 4 port (2 in 2 out) model. The old cans were 2x Mishimoto compact catch cans (2 in 1 out utilising 1 in 1 out on each).
This is the new set up. When the car is connected like this the car will do as described in initial post.<br/>This is an aggressive sway from 500 rpm to 1500 rpm and AFR going from about 11 to almost full lean.
This is what is ment when I disconnect the system like shown the issue goes away. Even with this vac leak the car compensates as expected and idles ok.
This is the old set up which is using the exact same hoses as the new set up. The only difference is that there is two smaller cans vs the new single bigger can. I have reverted back for repeatability and the issue is not present.
This was a test I did where I routed the new set up inline with one of the older small cans and blocked the un used port on the intake. No issues.
I’m assuming your still running the MAF. If so, then what ever your changing to as a setup is resulting in pulling in unmetered air after the MAF which may cause the rpm and AFR issue.
Stock setup has a return hose from the side of the valve cover to the intake pipe post-MAF. He's not introducing anything that wasn't there when the car was stock (other than maybe a slight increase from an additional port). Even then, the setup worked fine for him in dual can configuration.
But I want them to be recirculated and I dont understand why it is having issues doing it.
Do a check to see how much blowby pressure you're getting at idle. The new catch can is allowing too much gasses through and reduces the airflow through your MAF enough where it is either out of MAF low range reading ability or in a flowrate not programmed in ECU map. Try connecting one to barb like in your sketch and connect other to the stock intake manifold location.
*if connecting hose to intake manifold doesn't help, then I'd try plugging the 2nd nipple on intake pipe and connecting check valve to that hose and a breather element to vent the extra pressure to atmosphere.*
My 2 cents.
Last edited by 2006EvoIXer; Aug 4, 2017 at 08:27 AM.
The only correct way to fit a catch can is to fit 2 of them, one in line with the PCV valve, the other in line with the vent pipe.
Doing it any other way disables the the flow of air through the crankcase , the oil ends up getting contaminated with water and fuel.
You'll know this when you give it the sniff test.
You'll probably find your main problem when you take a good look at the sparkplugs.
Intake manifold vacuum is applied to the crankcase via the PCV valve, drawing fresh air into the crankcase via the breather. The airflow through the crankcase and engine interior sweeps away combustion byproduct gases, including a large amount of water vapour which includes dissolved chemical combustion byproducts. This mixture of air and crankcase gases then exits, often via another simple baffle, screen, or mesh to exclude oil droplets, through the PCV valve and into the intake manifold. On some PCV systems, this oil baffling takes place in a discrete replaceable part called the 'oil separator'.
First of all I would like to thank you all for your responses.
I have logged the car at idle and introduced the catch can into the system and it instantly effects the Airflow Hz reading. When idling normally I expect to see 31.2-37.5 as the two common values however when the catch can is connected closed loop back to the intake this will go erratic and up to 75 at times.
I have attached a graph created from the CSV log of the Airflow Hz for you to see.
Again I am not looking for opinions on how a system should be set up, I am asking the brains trust for possible reasons that this particular catch can causes this reaction. And other cans do not.
*Things I have tried since*
- I removed the baffle inside the can as I thought it would cause virbaration in the can causing the MAF Hz Issue. No change.
- Added Fuel safe foam mesh into can to create restiction and dampen any pulsing of the crankcase gases.
- Un mounted it to prevent all chances of chassis vibration.
- Moved in all orientations to see if that made an difference
Again, If I install the old 2 can set up the car idles perfectly in the same routing. As you can see 5 distinct sections.<br/>Stable/Issue/Stable/Issues/Stable
