Vented Oil Catch Can = Bad Idea
05-06-2011, 11:42 AM
#1
Vented Oil Catch Can = Bad Idea
Sorry if this is a repeat of some point made in the other bazillion posts on the subject of catch cans, but I learned something kinda important in the 1775 miles I put on the car last weekend in the run to Deal's Gap and back. After deciding to go with a catch can and not much time to do it before leaving, I did the simplist possible version which was to take the line from the oil filler neck and run it (with a small filter) into an open can (Venom Energy Drink for extra hp, lol). I then blocked off the nipples into the lower intake manifold where the line normally goes ('06+). On the trip down, I noticed my highway mpg wasn't what it should be. While there, a fellow rotarhead (sorry, your name escapes me) saw this setup and related that it had caused problems in getting a stable a/f reading for tuning on his car. Humm. After that, I watched my a/f command and actual settings, and caught it several times doing bad things. In particular, with cruise control on at 73 mph, every time the road went uphill, the command would remain at 14.6, but the actual would drop as low as 13.4 and stay there. It would come back right away if the road then went downhill or after a minute or so after leveling out. After seeing that, I returned it to the stock condition. Afterwards, with the same cruise setting of 73, the a/f sat steady at 14.6, uphill, level, and down.
What's causing this to happen, I haven't a clue, but happen it does. When there's time, I'll add a "catch can" that works more as an air/oil seperator, that is a sealed can in the crankcase vent line, with the vacuum line plumbed intact from the lower intake maifold as per stock.
Anyone else notice this effect? Any ideas why venting that line causes these problems?
What's causing this to happen, I haven't a clue, but happen it does. When there's time, I'll add a "catch can" that works more as an air/oil seperator, that is a sealed can in the crankcase vent line, with the vacuum line plumbed intact from the lower intake maifold as per stock.
Anyone else notice this effect? Any ideas why venting that line causes these problems?
05-06-2011, 11:48 AM
#2
While I don't have any A/F readings, on my '06 mine still nets the same mpg (17~18 city, 21~23 highway) and I don't notice any performance issues. It shouldn't make a difference considering by original design it's vented regardless; it breathes up through the LIM to the UIM through the throttle body through the intake filter. It wasn't completely sealed off before either.
Perhaps one of the tuners (MM) or Charles from BHR can comment on if they've found this to be troublesome in the past
Perhaps one of the tuners (MM) or Charles from BHR can comment on if they've found this to be troublesome in the past
Last edited by Vlaze; 05-06-2011 at 11:53 AM.
05-06-2011, 12:51 PM
#3
Did that... Did it differently, but did it.
Sounds like the 2006 plus configuration. What you did was change how much air is fed into the engine. Air from the crank case was vented that direction. It is now not vented in that direction. How much depends on a ton of stuff, but at a minimum, the ECU is trying to figure out what is going on. Before you had air going into the engine that was not going through the MAF, and that was cool. Now, you have lost that air. My problem was the opposite.
Your real catch can plumbed in line should be fine once you get it all together.
You could test the ECU confused theory by resetting the ECU, letting it re-learn, then attempting to repeat the problem.
Sounds like the 2006 plus configuration. What you did was change how much air is fed into the engine. Air from the crank case was vented that direction. It is now not vented in that direction. How much depends on a ton of stuff, but at a minimum, the ECU is trying to figure out what is going on. Before you had air going into the engine that was not going through the MAF, and that was cool. Now, you have lost that air. My problem was the opposite.
Your real catch can plumbed in line should be fine once you get it all together.
You could test the ECU confused theory by resetting the ECU, letting it re-learn, then attempting to repeat the problem.
05-06-2011, 12:55 PM
#4
IIRC there are 3 lines fed to the air intake for breathing, the crankcase is one of them, another is from the UIM and 3rd I can't recall. For the '06+ models, the LIM lines go to the oil filler nipple IIRC, so removing them from the LIM and feeding them directly to a catch can shouldn't change anything in regards to performance. The other 3, I capped off the line from the UIM to the intake and left the other 2 in, 1 being the crankcase line and the other one I can't recall.
05-06-2011, 01:08 PM
#5
No that is not correct.
On the newer style breather systems there are 2 lines. 1 from the filler neck to the LIM and the other is at the bottom of the filler by the dip stick. That one connects to the the intake tube post maf. So any air that was being pulled in to the LIM from the breather was metered air.
Now what you have is the intake trying to pull in unmetered air into the intake tube through the breather system and your catch can. Thats your problem. Under closed loop, the ECM was adding fuel, but in open loop it was lean. Under WOT you would not be getting a ton of air because the breather system will only allow so much, but I promise you, you were a little lean.
Last edited by Highway8; 05-06-2011 at 01:10 PM.
05-06-2011, 01:15 PM
#6
This is only true if you route the lines from the '06+ models that were on the accordion to the catch can. For those models what you should be doing is only routing the one from the filler neck to the catch can and capping off the 2 at the LIM. It shouldn't effect anything.
05-06-2011, 01:23 PM
#7
This is only true if you route the lines from the '06+ models that were on the accordion to the catch can. For those models what you should be doing is only routing the one from the filler neck to the catch can and capping off the 2 at the LIM. It shouldn't effect anything.
But no, thats exactly what the OP did and on the new style breather you have to connect both vacuum lines ( filler neck and the lower by the dip stick) otherwise you get unmetered air.
I am not trying to be rude, but please read my explanation again.
I have a 07, with a supercharger and a catch can. I learned from trial and error.
05-06-2011, 01:28 PM
#8
I believe the issue was with your terminology; stating "breathing system" sounds vague and hard to connotate what you're referring to when mentioning 2 lines when there are 4 in question total (Oil filler & 3 on the accordion). In theory since the hose from the intake mounts directly under the UIM, personally I don't see the function of it since air will inhabit the UIM regardless. I capped that off and still have no difference in running that I notice. Perhaps an actual tune will state otherwise, but it won't say vacuum leak since I capped it off and am not running it to the catch can. My power and mpg all are still acting the same.
From what the OP stated, he said he only took the oil filler neck nipple and routed that to the catch can, practically exactly what I did so the rest is moot for his situation.
From what the OP stated, he said he only took the oil filler neck nipple and routed that to the catch can, practically exactly what I did so the rest is moot for his situation.
Last edited by Vlaze; 05-06-2011 at 01:34 PM.
05-06-2011, 02:00 PM
#9
What I'm picturing of course is the route filler neck --> LIM without noticing that there is one line at the lower dipstick going to the accordian post-MAF. Thanks for pointing that out Highway8! I wonder what the purpose of that is (idle stabilization?) and whether capping it has any ill effects? It also perhaps explains why the throttle body had some oil residue on it last time I had it out. I only noticed it going rich, not lean, but of course without data logging, it might be possible to miss the change. With the open can, the mpg variation is maybe 1 mpg which could get lost in the noise if that's the only data one has, however the variations in actual vs. command afr's as described above were very clear and repeatable.
05-06-2011, 02:06 PM
#12
I believe the issue was with your terminology; stating "breathing system" sounds vague and hard to connotate what you're referring to when mentioning 2 lines when there are 4 in question total (Oil filler & 3 on the accordion). In theory since the hose from the intake mounts directly under the UIM, personally I don't see the function of it since air will inhabit the UIM regardless. I capped that off and still have no difference in running that I notice. Perhaps an actual tune will state otherwise, but it won't say vacuum leak since I capped it off and am not running it to the catch can. My power and mpg all are still acting the same.
From what the OP stated, he said he only took the oil filler neck nipple and routed that to the catch can, practically exactly what I did so the rest is moot for his situation.
From what the OP stated, he said he only took the oil filler neck nipple and routed that to the catch can, practically exactly what I did so the rest is moot for his situation.
Yes 4 lines total but this is a catch can install problem, so I was trying to avoid speaking of the other lines. #1 & #2 are for the Crankcase oil ventilation system. #1 filler neck to the LIM, #2 Oil filler by the dipstick tube connects to the Intake accordion tube. #3 goes to the OMP valves and #4 goes to the jet air.
The reason for the newer style Crankcase oil ventilation system is so the oil does not make its way into the throttle body and through the entire intake system. What they did was vent the Crankcase oil ventilation system straight to the LIM bypassing everything which is sensitive to oil. The reason for the second vacuum line at the bottom of the oil fill tube is to equalize the pressure in the Crankcase oil ventilation system. If they only sent the line from the oil fill neck to the LIM you would create vacuum in the Crankcase oil ventilation system, ask me how I know.
What the OP stated he did was remove the oil filler neck line (#1) and route that to a catch can. The problem was created because he left the second Crankcase oil ventilation line (#2) connected to the accordion tube. That created a vacuum leak which is causing him to run lean.
He stated that prior to the catch can, under normal cruise conditions the AFR was in the 14's (closed loop) but when he goes up hills it drops to 13's (open loop).
After the catch can install it would be in the 14's in closed loop but when it switched to open loop it would not get richer and in fact it got leaner. Ding ding ding thats a vacuum leak.
Last edited by Highway8; 05-06-2011 at 02:13 PM.
05-06-2011, 02:12 PM
#13
To fix the problem you can do 1 of 3 things.
#1 connect the catch can to the LIM instead of leaving it open to the atmosphere. So basicly any oil that would have gone to the LIM is being caught up in the catch can.
#2 route the second Crankcase oil ventilation line #2 to the catch can using a Tee and cap off the line at the intake accordian tube.
#3 Cap both sides of line #2.
#1 connect the catch can to the LIM instead of leaving it open to the atmosphere. So basicly any oil that would have gone to the LIM is being caught up in the catch can.
#2 route the second Crankcase oil ventilation line #2 to the catch can using a Tee and cap off the line at the intake accordian tube.
#3 Cap both sides of line #2.
05-06-2011, 02:13 PM
#14
I didn't mess with the intake neck hoses, but looks to me now like I should have, removing and capping on both ends the one running from the lower dipstick to the accordian. Otherwise, if I'm understanding it right, air goes from the open catch can --> upper fill tube --> lower fill tube --> post-MAF accordian. Just don't know the function of that hose and whether removing & capping would have any negative effects. In principle, I'd like to keep crankcase fumes out of any part of the intake. Second best (and better for emissions) is to condense them in the can before passing the airflow on to the intake tract.
05-06-2011, 02:29 PM
#18
Oh, please do not confuse the plastic oil filler assembley with the UIM, they are both made out of the same looking black plastic and they are connected by 2 screws, but they are 2 seperate things.
When I keep saying the lower breather line by the dip stick tube, I am refering to the lower nipple on the oil filler assembly.
When I keep saying the lower breather line by the dip stick tube, I am refering to the lower nipple on the oil filler assembly.
05-06-2011, 02:34 PM
#19
Oh, please do not confuse the plastic oil filler assembley with the UIM, they are both made out of the same looking black plastic and they are connected by 2 screws, but they are 2 seperate things.
When I keep saying the lower breather line by the dip stick tube, I am refering to the lower nipple on the oil filler assembly.
When I keep saying the lower breather line by the dip stick tube, I am refering to the lower nipple on the oil filler assembly.
Yes, obviously they are
Anyhow, I stated UIM because that gets capped off when you resort to a CAI which I did, I just forgot that it didn't route to the intake on the accordion tube is why I confuzzled it up.
05-06-2011, 03:55 PM
#22
@Tamas,
If you install a vented catch can in an 04 or an 05, and run all 3 lines to it, you have installed a HUGE vacuum leak. An awful lot of air goes through the two other lines. Less goes through the Oil Fill line, but some goes through there as well. I have no idea how much or where it goes, but I was seeing air flow into all three. The number of lines you hook up determine the magnitude of the leak. It sounds like OP discovered that the oil fill does indeed consume air as well.
My opinion, is do not install a vented catch can, route the other end back to the intake, on ANY model.
If you install a vented catch can in an 04 or an 05, and run all 3 lines to it, you have installed a HUGE vacuum leak. An awful lot of air goes through the two other lines. Less goes through the Oil Fill line, but some goes through there as well. I have no idea how much or where it goes, but I was seeing air flow into all three. The number of lines you hook up determine the magnitude of the leak. It sounds like OP discovered that the oil fill does indeed consume air as well.
My opinion, is do not install a vented catch can, route the other end back to the intake, on ANY model.
05-06-2011, 04:08 PM
#23
I only plan on installing the catch can on my '04 with just the line from the oil filler neck leading to it.
By leading the other end back to the accordion tube, there is still the possibility of having oil vapors gumming up stuff, so that's why venting the can seems to make more sense as long as it doesn't cause some other issue.
By leading the other end back to the accordion tube, there is still the possibility of having oil vapors gumming up stuff, so that's why venting the can seems to make more sense as long as it doesn't cause some other issue.
05-06-2011, 04:15 PM
#24
Did this for the Turbo guys with the 06+ vac line layout . Same applies to NA .
If you attach the catch can to the filler neck then effectively what can happen in some circumstances is you suck in unmetered air as Hiflite pointed out . The stock setup is designed such that metered air flows out of the accordian tube, through the engine , out the filler neck and then back in through the LIM .
If you attach the catch can to the filler neck then effectively what can happen in some circumstances is you suck in unmetered air as Hiflite pointed out . The stock setup is designed such that metered air flows out of the accordian tube, through the engine , out the filler neck and then back in through the LIM .
Last edited by Brettus; 05-06-2011 at 04:50 PM.