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EVAP and purge valve with aftermarket throttle body?
Is it possible to use the 12a's purge valve if I'm using a different throttle body? I'm trying to figure out how it activates based on the diagram and it looks like it may need a vacuum source close to, but not under the throttle bodies. Is that correct? Would it be easier to just get a solenoid based valve and have the ECU control it?
I think I answered my own question after some investigating. The dark green hose does in fact connect to a vacuum source just above the throttle plates so it only sees vacuum signal when there is slight throttle application. The manual says the system should engage above 2,000 RPM.
Since I don't have a port like that on my throttle body I have two options: The first and most obvious solution is to acquire an FD electronic solenoid.
The second approach would be to rummage my parts bin and use the original FB valve along with a solenoid off the rats nest connected to the green hose. At idle deactivate the solenoid so the green hose doesn't see vacuum, above 1,500 RPM or so, activate the solenoid and the green hose will see vacuum and open the valve...up until the point there is no vacuum at full throttle, at which point it will close. It'll just require one wire from the ECU and a quite simple logic output.
I think I answered my own question after some investigating. The dark green hose does in fact connect to a vacuum source just above the throttle plates so it only sees vacuum signal when there is slight throttle application. The manual says the system should engage above 2,000 RPM.
Since I don't have a port like that on my throttle body I have two options: The first and most obvious solution is to acquire an FD electronic solenoid.
The second approach would be to rummage my parts bin and use the original FB valve along with a solenoid off the rats nest connected to the green hose. At idle deactivate the solenoid so the green hose doesn't see vacuum, above 1,500 RPM or so, activate the solenoid and the green hose will see vacuum and open the valve...up until the point there is no vacuum at full throttle, at which point it will close. It'll just require one wire from the ECU and a quite simple logic output.
either way would work, not sure you need the FD solenoid, any of them would probably work just fine.
Ok, so here's the plan. I cleaned off the right most solenoid on the rats nest as it has the vent on the front instead of the top or back like some of the others. I know the are moveable, but the parts can be quite brittle.
#1 will go to my vacuum manifold. #3 will probably go to the manifold as well but it would be better if it went to separate ports as the air traveling through will contain oil and gas vapors. I'll have to decide whether I want to drill and tap new ports for this. #2 connects to oil filler neck. And the charcoal canister connects like a normal FB using the lower center iron port and the vent tube to the gas tank.
Solenoid disabled:
#1 port is locked down, it cannot suck or blow air. The purge valve plunger is at rest, closed, and sees no vacuum pressure. Air cannot be sucked from either #2 or #3, however air can be blown from #2 into #3 if some force is applied. This represents positive crank case pressure or pressure from expanding fuel vapors in the gas tank being released while the solenoid is still in closed position...but it will not introduce a vacuum leak while running unless there was excessive blow by. This is not going on a turbo motor so it should be fine.
Solenoid enabled:
The purge valve sees vacuum from the #1 port and opens. It is not a vacuum leak because once the plunger is open no more air can be pulled from the port. Air can be sucked from #2 via #3 at this time although it is still rather restricted so it is not a huge vacuum leak but this is how the crank case and charcoal canister will receive fresh air from the check valve near the gas tank.
The solenoid is easy to activate via my ECU since it's just a digital on/off output. So there we go, I've just resurrected part of the rats nest for an EFI build. Hopefully it works, I'm a few weeks away from testing it as I still need to build a harness...but now I know to add one extra wire for this solenoid.
11-27-18, 03:52 PM
