How much of the funk built up in the intake plenum over time is from the PCV valves?
I also understand that it transfers pressure from the crankcase back into the intake, but what are the advantages? I have read some basic explanations, but I would really like to 'understand' the system. Pro's, con's, affects of clogged valves..and more. If this needs to be moved to the engineering section do so, I just think this section gets more exposure.
later
PCV funk
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Mayhem_J30
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Q45tech
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- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Long ago before EPA, engines sucked in air from a valve cover filter and the blowby left the engine by a pipe under the car.......all those petro fumes.Today the air is sucked into valve covers prior to the TB [having been measure by the MAF] and the PVC controls the amount of fumes returned to the plenum for burning.........after all they volatile oil products and a little unburned gasoline and soot wiped off the cylinder bores and air! Why waste them.
New engines have few fumes since the rings are new and engines run with SYN OIL have few fumes since the oil fractions don't evaporate until a higher temperature vs conventional oils.
High mileage even with Syn Oil have more blowby relatively.
If 60k cleaning is good during new to 60k, then 40k from 60k-120k, then even sooner 120k to 180k, then sooner interval thereafter.
Because of the way the impulses of vapor enter the plenum when the TB is snapped closed a film settles at the bottom where the TB rests and a small channel for idle air and 2 vents for vacuum is located..........this build up affects the minute flow of idle air [that air that always flows with TB closed.............as the flow diminishes the computer has the IAC open more to maintain the idle SPEED.......[the computer expects the IAC to be clean so that a certain percentage of opening translates to a known certain percentage of extra air [this is not the case with a dirty IAC].
The MAF is not very accurate at low flow rates [designed as a trade off to be very accurate at high flow rates].
Basically guessing at under 1,000 rpm [but an important operational check - is air flowing in], the rpm [from CAS] is tried to be maintained at 650 rpm [except when warming up as another declining rate rpm is chosen based on coolant temperature and time from start.
Rather than burden the ecu with a bunch of calculations, a hot wax device heated by coolant flow [called the Fast Idle Cam] in TB, PROPS the TB blade open an extra variable amount say to 1,000 rpm then the IAC is commanded to add zero to 300 rpm worth. The hot wax expander is like the carb choke in many ways except it is proping open the throttle blade..........the setting of this is very very critical and cannot be adjusted without hours and hours of work because you would need a variable coolant source [say -4F water, 32F water, 77F water and 104F water] to set the differential opening amount......twiddling here will always get things wrong!
So the time from prior to crank, crank, and warm up is a function of coolant temperature and after 90 seconds progressively more information is allowed from MAF........relative weights of each sensor in solving the equation of injector open time. Once the coolant exceeds 170 F the MAF is the deciding factor [called closed loop] since if the o2 are warm enough they could provide a stable signal [usually not at 650 idle except maybe in summer].
Back to PCV valve: this valve is different for each engine in that the spring tension and valve shape and opening amount is balanced to work with the exact correct vacuum of the engine so that there is no flow at off or backfire , little at idle or decel, and a lot at cruise and a little less at WOT acceleration or high speed.
The manual warns that with excessive blowby the PVC maybe overwhelmed and all bets are off.
Blowby may be from ring wear or exhaust valve stem seal wear.Obviously the better you change oil or the better oil you use when new you will prolong the time when the excess occurs.
New engines have few fumes since the rings are new and engines run with SYN OIL have few fumes since the oil fractions don't evaporate until a higher temperature vs conventional oils.
High mileage even with Syn Oil have more blowby relatively.
If 60k cleaning is good during new to 60k, then 40k from 60k-120k, then even sooner 120k to 180k, then sooner interval thereafter.
Because of the way the impulses of vapor enter the plenum when the TB is snapped closed a film settles at the bottom where the TB rests and a small channel for idle air and 2 vents for vacuum is located..........this build up affects the minute flow of idle air [that air that always flows with TB closed.............as the flow diminishes the computer has the IAC open more to maintain the idle SPEED.......[the computer expects the IAC to be clean so that a certain percentage of opening translates to a known certain percentage of extra air [this is not the case with a dirty IAC].
The MAF is not very accurate at low flow rates [designed as a trade off to be very accurate at high flow rates].
Basically guessing at under 1,000 rpm [but an important operational check - is air flowing in], the rpm [from CAS] is tried to be maintained at 650 rpm [except when warming up as another declining rate rpm is chosen based on coolant temperature and time from start.
Rather than burden the ecu with a bunch of calculations, a hot wax device heated by coolant flow [called the Fast Idle Cam] in TB, PROPS the TB blade open an extra variable amount say to 1,000 rpm then the IAC is commanded to add zero to 300 rpm worth. The hot wax expander is like the carb choke in many ways except it is proping open the throttle blade..........the setting of this is very very critical and cannot be adjusted without hours and hours of work because you would need a variable coolant source [say -4F water, 32F water, 77F water and 104F water] to set the differential opening amount......twiddling here will always get things wrong!
So the time from prior to crank, crank, and warm up is a function of coolant temperature and after 90 seconds progressively more information is allowed from MAF........relative weights of each sensor in solving the equation of injector open time. Once the coolant exceeds 170 F the MAF is the deciding factor [called closed loop] since if the o2 are warm enough they could provide a stable signal [usually not at 650 idle except maybe in summer].
Back to PCV valve: this valve is different for each engine in that the spring tension and valve shape and opening amount is balanced to work with the exact correct vacuum of the engine so that there is no flow at off or backfire , little at idle or decel, and a lot at cruise and a little less at WOT acceleration or high speed.
The manual warns that with excessive blowby the PVC maybe overwhelmed and all bets are off.
Blowby may be from ring wear or exhaust valve stem seal wear.Obviously the better you change oil or the better oil you use when new you will prolong the time when the excess occurs.