I have been having idle surge problems since I did my h/c about 1.5 yrs ago. I haven't been able to tune it out completely. I changed my A.I.R check valves, had my exhaust on and off a few times. Rewelded my O2 bung, check fr exhaust leaks at the connection points. I've had my intake manifold off and on so many times I can do it in about 10 minutes now. I also changed my 2 front O2 sensors and checked and rechecked my intake track. I have also tested for intake and exhaust leaks with the manifold and exhaust on the car, running, with propane, cigarette smoke, and water (on the intake). Nothing changed what I concluded was my problem. My LTFT's were ALWAYS higher by about 4%-8% on my passenger's side.My DS LTFT's were around -2% to -6% and my PS LTFT's were always +4 to -2%, but mostly on the + side and always at least 4% higher than the DS. Also, when idleing while rolling the car will almost immediately start to buck and surge rythmically untill it get's downright violent. I was able to tune this out a little but not entirely. I was getting frustrated to the point of taking out my h/c and other stuff and going a differnt route. Then came yesterday...
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I was responding to a post by Cobra4B yesterday and revisited an article he linked to regarding the PCV operation. This time I looked at what the article said about the state of the valve at idle, but in a 'stock' car. At idle there is appreciable vacuum in the intake manifold and that vacuum sucks the valve shut, 'so no unmetered air enters the manifold to alter the a/f mixture'. I almost went on then it hit me. I idle at around 50-53kPa. Stock was around 34-36kPa. My pcv valve is hanging partially open. Keep in mind I have a small cam too, but it's on a 112lsa. I removed the pcv hose from the intake and plugged the pcv fitting, then put a small 'breather filter' on the hose end I just removed. I then zeroed my LTFT's and started the car while running my EFILive scanner while scanning my LTFT's and O2's. When they started to track, they tracked together and after it was warmed up and driven for a bit, they were at -2.3% each at idle. There was still a little surge, but it was better than before and I'm thinking it's because my fueling at idle has to be redialed in to compensate for the error I tuned to.
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Now here is my dilemma, I guess, and it's the same as Cobra4B's. Can I just eliminate the the PCV and either restrict the air into the intake, my preference, or can I just put a breather on it and wear a gas mask while driving.
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Has anybody had success in altering the pcv valve to not open until around 60kPa. This way my idle would behave and I could still use the pcv.

 

Excellent question. I'm all ears.

 

I just reread the older thread about eliminating the PCV valve altogether. Is this a viable option with the 01-03 style valley cover? I've been to two tuners after my H/C, and later LS2-90TB/FAST install, and though off-idle it runs great, the idle is all over the place. Sometimes it settles right down @ about 825, sometimes it stays at about 1300 for about 10-15 seconds before eventually settling down, and sometimes it pogos from 1300-300 and back a couple of times, and dies. It also runs very rich, but only at idle. My tuner thought it was due to the ported TB, but though I installed a catch-can, the PCV is still in the line.

 

On the driver's side valve cover, the opening is the size of a PCV valve on other cars. I am wondering if there is a vacuum value listed somewhere such that you could possibly get a PCV valve from some other car and plug it into the driver's side valve cover. Only issue is the passenger's side valve cover would not be included as it goes from the valve cover to the "Y" in the line behind the intake. Not sure if you block that off and draw all air through the driver's side newly installed PCV valve (since the feed is on passenger's side) if this would solve it. You could easily hook it up over the top of the motor to try and if it worked out re-run behind the intake like normal. Most of the older motors are hooked up this way, draw from one side and feed from the other. Question is if PCV valves come in different crack pressures.

 

There's no driver side valve cover vent on the LS6. In addition, there's no port for the stock pass. side vent tube to TB on the LS2 90 TB. I've got the pass. side tube connected to the airbridge on mine.

 

vettenuts, interesting idea but I have done the LS6 pcv conversion. I was getting a lot of oil in the intake and at the time that was the next best thing to do for that. I also have LS6 valve covers and they are hogged out as large as possible without going through them to fit my Jesels.
The $64 question. I wouldn't be opposed to finding the right one and having to mod it or make some kind of fitting to make it work. The main reason I'm bringing this up is because I'm wondering if there are others out there like zeevette that have similar problems and haven't been able to pin it down. I'm wondering about maybe a turbo or sc application pcv.

 

The later >02 cars did not have a PCV "valve" just a shell with a restriction. (below).

I have tried a dozen different iterations to stop ingesting oil and maintain vacuum during track days. Below is the latest which actually works!
It is elaborate but nothing less really works.
The large line out of the filler is large to decrease velocity and keep from atomizing the oil. The catch can is vented to atmosphere via filter in lid and there is a very restricted, about size of PCV hole below, line going from can to the intake port to prevent the can from huffing, particularly at idle. Unmetered air is not an issue because it is minor amount, fairly constant and is "tuned for" as part of AFR. This whole setup minus the line to the intake is lifted from Nascar teams.

 

see5 that looks like a sweet setup and most likely what I'm looking for. Forgive me but I have a few questions.
1) It's not clear to me where the big line coming from the filler cap ends up. Does it go to the catch can?
2) I see the smaller line going from the catch can. Does it go to your valley cover connector or to the intake. If valley cover, I don't see where the intake connector is. If intake connector, I don't understand how to connect to the valley cover.
3) The catch can looks like a vented vacuum can that can be purchased at Jegs or Summit, am I correct?
4) Is that the part number of the cap with small hole in it on the package it is sitting on?

 

Heres a little trick. completely eliminate the pcv valve and run a longer line from the valvecovers down to you air filter area and plumb your pcv lines into the intake right after the air filter or before if you are worried about oil. This way all the air is measured because it still goes through the maf. and the intake will draw a slight vacuum as you increase engine speed due to air filter resriction. Which is the time you pcv valve would open anyways. Then just plug all the pcv fittings on the tb and intake manifold. Hard lesson learned though if your car sucks oil through valve covers get a catch can or it will foul the maf and youll have to clean it all the time. This is a trick I use for s/c application since the pcv valve doesnt work for them either.

 

Will this work? ts a .3psi cracking pressure check valve..

http://www.mcmaster.com/
Part# 7775K53

 

Interesting read.

Link

 

You have make that up from your stock cap. You can use a trick racer fitting ($40) or a Home Depot plastic 90 with rubber hose instead of Aeroquip. The hose is longer so the oil fill cap can be rotated for removal.

 

see5, 'I see now', said the blind man. Thanks for the clarification.

 

Thanks, I kept a link to that part number. I have to find a conversion formula to convert specific gravity of liquid to air to determine if that valve would work.

 

That's good info and something I hadn't considered. Flow volume at different opening points. And what are you doing up and on the internet at 5:05 AM?

 

I'm going to try this approach first, since it involves the least cost and labor. I also have all I need on hand.

 

Here is something I dug up: Billet pcv valve What's interesting is I can change the pcv valve by removing a snap ring. I could put a different spring in to alter the crack pressure.

 

Hi I am using atmospheric breathers on my hds/cam engine without any problems or oil smell---I have a breather on the rear of the drivers side valve cover plugged into the port.Then I have a breather connected with a hose to the front of the pass. side valve cover nipple--Also i have an oil filler cap that has a one way check valve in it so it will draw in air. I still use the PCV valve with a colescing filter .As far as un-metered air going thru the maf--the change in LTFT's was very slight but I made some small adjustments and the #'s are all 0 or slightly negative.I had some idle surging as well but I corrected that with the desired airflow table and the base timing "in gear" and in "P/N".


PS--intake manifold is oil free---I'm in Calif--when going to the smog police I have to take off the atmospheric stuff and go back to stock

 

Great post!!!

 

How can you maintain a vacuum in the crankcase? I see that its vented and im sure that works great to relieve positive pressure but how are you maintaining a vacuum w/ something that is vented and has a tiny line to the intake.