Is there a general consensus on this? *Check Valve in Line with Stock PCV? *Check Valve - No PCV.
*Block/Plug-up PCV when racing..... Will the Check valve help prevent rear main leakage?.. yada. yada. yada.
I didn't find anything really solid in the archives. It seems to be a somewhat debatable topic.
---Any input/ideas is appreciated!
John
If you absolutely have to use a check valve, which BTW I don't recommend. Then use it in line with the PROPER PCV.
Remember, this is a Mass Airflow System on these cars, and every bit of air going into the engine MUST be accounted for!
Think of the PCV system as a calibrated vacuum leak. It's accounted for in the MAF calibrations.
The PCV allow "just so much" air through during vacuum, and the check valves allow huge amounts through, unfettered!!
Is there boost leak around the PCV during boost? Yes, but it's a lot smaller than most people think!! They try blowing into the PCV and it seems like there's a lot of air going through, it's actually a very small amount, and when the boost pressure really comes up, it seals the PCV even better. We can't produce anywhere near the pressure with our lungs that the turbo can.
TurboDave
Dave,
My understanding is a positive crankcase ventilation system draws air into the engine through the oil filler cap or the air cleaner/MAF and circulates it through the engine. The air combines with vapors in the crankcase and exits the engine through the PCV valve mounted in the rocker arm cover (intake for us). The air vapor mixture than re-enters the engine through the carb or intake manifold and passes the combustion chamber where it is burned.
I'm not sure how this concept differs in our boosted cars. I thought that a check-valve in the hose between the intake and the PCV valve would be so boost won't blow into the valve cover (and through the rear main seal).
***Calling Ken Mosher....I think I read in the archives that you bought an ace hardware special "valve" that you ran "closed" when racing.
Is anyone doing anything different?? I've got a solid high 11 recipe car and have run up to 25lbs of boost (w/Race gas). The engine has never been taken down and I want to tweek everything just right.
Thanks!!!
This little valve is just a brass shut off valve (in the plumbing section) that I used to use to make sure there wasn't any pressure sneaking past the PCV.
I have it laying around here somewhere, but don't use it any more. I found that using the AC Delco valve works a lot better than the Fram ones.
Your understanding of the PCV operation is correct. It's needed to vacate vapors and such from the crankcase, helping to alleviate corrosion, etc. from acid buildup in the crankcase.
It's is as I said a "calibrated" vacuum leak and is accounted for in the MAF's calibration setup, in the MAF its self. Changing the operating curve, by removing the PCV, or otherwise modifying the air it passes can, and does cause problems in the state of tune, simply because unmetered air is either too high or non existent.
Probably the primary reason you see so many posts on all the bulletin boards asking "why are my BLM's all jacked around?" or words to that effect.
For what it's worth...
I have an ATR PCV/check valve in place of my original PCV valve. The point of this piece is that it's supposed to act like a PCV and check valve in-line. I don't know if it seals any better than a stock PCV valve under boost, but I do know that it didn't affect the idle quality of my car. I pulled 14" vacuum in drive-idle before and after I installed the part. That tells me that the PCV part of it is probably working OK.
Mike, it's the ATR piece that I specifically refer to, and try not to name names. It has complete unrestricted air flow in the vacuum direction, and that's the bad part. The check valve part of it works as advertised, but not the vacuum side.
I'd be interested to see what your BLM's look like at idle both in gear and park.
Dave
I'm not trying to start a war or anything. All I can say is that in my experience, the check valve hasn't seemed to have any negative impacts on my car. Here is what I have seen since I've installed the check valve:
1. My car idles at 14" Hg vacuum in Drive and 17-18" Hg in Park. That' pretty much normal, from what I know.
2. I noticed no degradation of idle quality when I installed the part. I imagine that the IAC is just going to a slightly lower step value with the check valve in there, so the amount of air entering the cylinders is about the same. If anything, the extra air might help me with my new, bigger injectors :-).
3. I dug up a Directscan file from last year, when I had a stock PCV valve. At the time, my car had stock injectors, a stock turbo, and a nearly stock chip. As you can see, even with the stock PCV valve, the computer needed to richen-up at idle:
150|150|128|128
128|122|125|134
128|128|115|108
128|128|128|137
Here are the BLM's from one of my Directscan files this year, after installing the check valve. Again, stock turbo, stock injectors, but a different chip (should be same BLM calculations, though).
150|146|132|128
128|128|120|124
128|128|129|118
128|128|128|130
Not a whole lot of difference. I looked through about 10 data files from both before and after I installed the check valve, and the two idle BLM's (150 and 146 above) have always been somewhere between 128 and 156, both before and after I installed the check valve. They usually tend to settle out in the 140's or 150's after I've had the chip installed for a while.
I admit that a true PCV is probably better for street driving, but on my car it doesn't seem to make a lot of difference. I can't say that I've seen any negative effects, except that the check-valve whistles louder than the PCV did. Based on all of this, I might go ahead and reinstall a PCV inline with the check valve, just to make sure. I suppose that the extra air volume at idle might be causing more oil to be sucked-up into the check-valve (called "oil pullover" in the auto industry). That would be a negative, if it's happening.
Sorry for the short novel. I just wanted to be clear about my experience. If you've read this far, congratulations!
Respectfully,
Mike Mshar
Mike,
Respectfully, not a very fair comparison actually. Since both BLM tables indicate that neither chip was any where near optimized, OR, you had a vacuum leak to begin with.
150 BLM's in any cell is unacceptable, and both of your idle cells are there or very close.
So the fact that there is/was a pre-existing problem doesn't mean things are "all right".
Still a lot of tuning to be done there ;-)
TurboDave
For what it's worth...
Your comments on my high BLM's at idle were worrying me a bit (like I don't have enough to be worried about, thanks!). I did some digging into my chip's code to see if anything was amiss. I found that in address $432, whoever made the original chip entered an "FF". If I understand correctly, this forces my ECM to wait 255 seconds before it can enable open-loop idle mode. So, my ECM was chasing a cold, unresponsive O2 sensor (I don't have a heated one) while I was sitting at a stoplight. This is bad, since my casual observations indicate that the O2 sensor cools-off pretty quickly at idle, like 10 or 20 seconds.
I was planning on buying a heated O2 sensor, anyway, so I'll probably just leave the chip code alone. I belive that this will lower my idle BLM's.
For anyone else who's having idle problems, you might want to look into this.
Thanks for worrying me, Dave!
Mike
Just my .02$ guys,
My '86 GN developed a mysterious Code 44 a couple of years back (lean exh. condition). It'd stumble off-idle (except with the MAF unplugged) then the motor would die when you plugged the MAF back in. BLM was maxed out. It would go to "open loop" mode at the same time the Code 44 would come on. It "bucked" at speeds less than 40mph like a standard trans thats in too high of a gear. Short story long, after replacing every sensor and the PROM I'd all but given up when one of the list members asked if I had one of the brass "positive seal" check valves installed. He'd run into the same thing. Voila! I removed it, put a new stock check valve in and the car had a completely different personality!
Hey Mike, just wanted to let you know that the FF you found at location $432 is there to disable Open Loop Idle Fuel Mode. Since this mode doesn't work, it is supposed to be disabled. Our cars start in O/L then switch to C/L based on temp ($405), and time (either $401 or $403). The O/L Idle Mode is not used. You might still have a problem with the O2 sensor, but its not related to location $432.
Thanks for the heads-up on the O/L idle mode. The table that I have for the stock chip's code shows address $432 as being set to "01", which would mean that the car can go into open loop idle after 0 seconds of idle time. However, when I looked at the actual stock chip code, I saw that this value was set to "FF", which disables O/L as you mentioned. I guess the table that I have is not 100% accurate.
I don't know if it's a characteristic of all of the Buick's, but my stock O2 sensor would slow way down during long periods of idle (more than 15-20 seconds). I have always worked with heated O2's, so I was surprised to see how the ECM would still chase the sensor even though it was obviously getting cold. I guess things were different in 1986. Anyway, the new heated O2 works great!
Regards,
Mike
Just for clarification. The stock chip DOES have a 01h value in location $342.