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Did you buy the car with the catch can already installed? Just throwing a guess out here , but Maybe the previous owner messed with the maf table values in the tune (assuming that table is changeable) ? Did you check the maf table values? The reason I'm assuming this is because when you introduced a leak intentionally that should make the car run worse not better.
Did you buy the car with the catch can already installed? Just throwing a guess out here , but Maybe the previous owner messed with the maf table values in the tune (assuming that table is changeable) ? Did you check the maf table values? The reason I'm assuming this is because when you introduced a leak intentionally that should make the car run worse not better.
My 2 cents:
At idle, it is supposed to have complete burn. Adding a little more air (leak) doesn't affect the complete burn since the oxygen sensor will add more fuel to compensate in closed loop. At idle, it isn't much more fuel.
Interesting theory. But this is only when engine is cold. Once hot, water vapor isn't condensing. If cold air is drawn from air filter pipe in front of turbo inlet, then water vapor can condensate under valve cover. The PCV won't able to pull enough vacuum to clear all the condense. I think I'm going to add check valves on both vents now.
Originally Posted by RightSaid fred
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'.
Last edited by 2006EvoIXer; Aug 7, 2017 at 10:47 AM.
Hi. I have a similar issue. I have 2 -8 lines from valve cover one is in the original vent location and the other is just adjacent to the pcv line where it is baffled in the valve cover. They go to a single sealed catch can with a single 1/2” line to the intake tube. And get the same swing in afr as op. I have tried putting a T in the line between the occ and intake tube with a check valve to allow any positive pressure pulses from cc to vent under idle and pull vacuum under boost. Still has rich idle issues. Installed a destructor in the line just before the intake pipe to get it closer to stock size and still has issues. Disconnect it from the occ and idle is good again.
This is interesting. Could the blowby at idle force it's way through catch can and into intake pipe and cause a venturi effect and suck fresh air through MAF?
What I would do is add splitter connected to a big check valve (1/2"?) and a crankcase air filter to bleed off any pressure from valve cover. That way, the pressure won't make it to intake pipe when turbo is idling.
Originally Posted by 00VIII
Update:
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
The first and last should be the same. The 2nd would be a problem when boosting because without a check valve at the VTA, fresh air could be sucked in and cause lean conditions since MAF wouldn't know to add fuel for this extra air.
Originally Posted by 00VIII
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.
