Quote:
Originally Posted by xsnapshot
^What? Don't spread miss-information. The ECU does NOT take into account "fuel vapor" as part of the fueling process. And how does "fuel vapor" come from oil? It doesn't. What happens if one engine has more blow by than others? How would the ECU account for that? It doesn't.....
The PCV valve is responsible for what it's name implies; Positive crank case ventilation and it's purely emissions related. It sucks up blowby gasses/oil and deposits them into the intake tract, where they are ingested/burned. This is much cleaner than venting to atmosphere.
The blowby/oil could be considered a performance detriment, as Its been shown to lower the effective octane of the mixture in cylinder. If you don't mind breaking a few laws, then vent the crank case to atmosphere and plug the intake ports. Just make sure your atmospheric vent is free flowing enough that pressure is not building up in the crank case from blowby. I will repeat that.....check your vents/filters regulary because you do NOT want pressure building up in your crankcase.
It could also be argued that leaving the PCV system in place will help minimize pumping losses, as it places the crankcase under a vacuum, which reduces resistance on the rotating assembly. This resistance however, is extremely minimal, and I doubt you'd notice any measurable reductions in mpg or horsepower because of it.
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Ya know, I rather take a bit of offense to you saying I am spreading incorrect information because I am not. You are.
Blow-by is what leaks passed the piston rings on the power stroke - "It sucks up blowby gasses/oil and deposits them into the intake tract"....yeah....that stuff. Guess what blow-by is???? 70% unburnt HC's - raw fuel. PCV is to prevent a positive pressure buildup in the crankcase (as a result of blow-by) and to prevent FUEL DILUTION of the engine oil, which causes corrosion of internal engine parts. It's also why PCV valves are designed to close completely on backfires to prevent fuel vapors in the crankcase from being ignited. The fact that a little bit of engine oil gets sucked up into the PCV in the process is the problem that people install catch cans for.
Our engine, as most these days, uses a variable-orifice PCV valve....at low load and high vacuum, it flows less, whereas at high-load and low-vacuum it flows more (because high loads produce much more blow-by), i.e., it accurately matches ventilation flow with blow-by production. Do you REALLY think Nissan (or any manufacturer) is going to design an engine that completely disregards PCV flow into the fuel map? NO. It is correct that no two engines will produce the exact same amount of blow-by at a given load value and there are differences from engine to engine as to blow-by characteristics. Saying the ECM doesn't compensate is just plain dumb. No two injectors deliver EXACTLY the same amount of fuel, no two air filters or intake manifolds deliver EXACTLY the same amount of air, no two engines are EXACTLY alike. That is why we have a closed-loop feedback control system, i.e., an AFR sensor (or O2 sensor depending on your application). It's basically the ENTIRE reason vehicles are controlled by a computer these days. The three-dimensional map of long- and short-term fuel trims is how the ECM compensates for not ONLY PCV variation, but variation in anything that would affect the AFR, e.g., wear and tear.
So yes....if you use a crankcase breather and disrupt the PCV system, the ECM will readjust and it probably won't be enough to upset driveability. But without manifold vacuum continuously cycling fresh air through the crankcase, I wouldn't even want to take the chance of fuel dilution and corrosion of internal engine parts. A catch can is a much smarter idea than just deleting the PCV, and a catch can can be fabricated for <$10 with an air compressor moisture trap from Home Depot or Lowes. Did it myself and it works well. Plus, you have the added benefit of knowing that when the catch can starts catching lots and lots of oil in there that your piston rings need help.
Late,
Trav