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Discussion Starter · #1 · (Edited)
Anyone knowledgeable enough to critique this EVAP concept?

Basically I think I'd like to keep the oem charcoal canister and basic fuel tank vapor control arrangement that is obviously well-sorted out by Toyota, and then simply control the EVAP VSV (purge valve) with my Link ecu. This way the charcoal canister will continue capturing vapors to keep fuel smell down, and I can calibrate the EVAP VSV to cause the engine (under vacuum) so suck on the charcoal canister.

Here is my basic concept: (this is incorrect, see downthread for updated schematic)



It seems the CCV and Pressure switching valve are only there to allow the OEM ecu to diagnose the system for leaks and non-operational switching valves. I don't care about those things, I just want a charcoal canister that absorbs fuel vapors and a way to evacuate them when engine operating conditions are right. This will capture about 95% of the intent of the EVAP system without a lot of extra diagnostic complications.

However I'm not sure I have my brain wrapped around the entire theory of operation of the system to be confident my rearrangement will work. For example, how is make-up air supposed to get into the tank. Put another way, when EVAP VSV is open and the charcoal canister is exposed to engine vacuum, it seems like there needs to be a way for fresh air to back-fill the tank's vapor dome with fresh air - and I don't see how that happens.

I have a couple spare analog inputs so I could potentially hook up the fuel tank pressure sensor, perhaps I could use that as an input for calibrating the EVAP VSV, though that doesn't seem necessary...

The Pressure Switching valve would be left in place but not hooked up.

Anyway, look it over and provide thoughts, please.
 

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The pressure switching valve looks like you said only for the ecu code setting. There looks to be a port/ vent right before thevsv valve. Maybe some sort of emergency vent valve? I wonder if the CCV valve opens to let fresh air in. There's also another hose on the left side of the charcoal filter that's unlabeled.
 

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Discussion Starter · #3 ·
I'm pretty sure the CCV is a pulsewidth modulated valve, and is intended to throttle fresh air into the canister. The EVAP VSV is not PWM, so it's just open or closed. Thus, with EVAP VSV open, the ecu can flutter the CCV to achieve a suitable differential pressure to create suitable flowrate.

I'm almost positive the Pressure Switching Valve (PSV) is there only to allow the ecu to isolate the canister from the tank for leak diagnostic purposes.

I'm not sure it matters to under theory of operation, but I can't say for sure I understand the fuel filler checkvalve. Which way is this meant to allow flow? My best guess is in ONLY allows flow towards the charcoal canister. I think this is why the pipe from filler neck to the checkvalve is depicted higher than the check valve - attempting to prevent fuel high up in the filler neck from actually being able to make it to the checkvalve - where it would be allowed to pass onward to the canister. If you were to basically seal the gaspump nozzle into the filler neck and force more fuel in - the fuel could be forced "over the hump" towards the checkvalve where it would go into the canister...which is why the manual says to stop pumping fuel once the nozzle "clicks".

The checkvalve only allowing flow towards the canister would therefore prevent any vapor captured in the canister from escaping - which seems inline with the intent of the system.

Last, the schematic depicts two "blocks" on top of the canister. Each block has what appears to be an unterminated line coming out of it (pointing to the left in the schematic). I'm confused what these are. The fact they are shown as unterminated makes me think they are open to atmosphere - but that makes no sense to me.

Anybody know what's up with these two lines?

There looks to be a port/ vent right before thevsv valve. Maybe some sort of emergency vent valve?
That is depicting the EVAP service port underhood. I'm sure you've seen it; it has a green screw-cap covering a schrader valve.
 

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Discussion Starter · #4 ·
Anybody know what's up with these two lines?
I think I can answer this. Per the schematic below, there is also an "air drain hose" with a small plenum on the end - it forks off to the Vapor pressure sensor as well as the CCV side of the canister. Because the end of the air drain hose is sealed/deadheaded - those two "unterminated" lines in first schematic are unimportant to the flow function of the system.



So I think I've got my brain mostly wrapped around this:

1. There is a checkvalve at top of tank that only allows flow OUT of the tank and TOWARDS the canister. Mechanical design is intended to prevent liquid from getting to this point where it could spoil the canister

2. There are two vent lines running from tank to canister; one has a checkvalve preventing backflow to tank, the other has a Pressure Switching Valve that can either allow or disallow flow/communication between canister and tank. By closing the valve, the tank and canister are isolated for individually diagnosing leaks in the canister OR tank.

3. There is a vapor pressure sensor for diagnostic purposes. I suppose it could also be used as an input to the ecu to help trigger/control purging.

4. There is a canister closed valve (CCV) to allow fresh air in from the air filter so a vacuum is not created in the fuel tank and EVAP system. Additionally, this valve can be closed along with the EVAP valve and Pressure switching valve to completely close off and "seal up" everything inside the canister.

5. There is an EVAP valve that allows engine vacuum to suck on the canister, pulling vapors into the engine where they can be burned. The CCV opens enough to prevent this from creating a vacuum in the fuel tank and EVAP system.

6. There is an air drain hose - Not sure on this one. Perhaps for any water condensation that develops? Maybe a small vacuum reservoir? Open to suggestions, here.
 

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Discussion Starter · #5 · (Edited)
In terms of making this system jive with an aftermarket ecu:

The Pressure switching valve would not be activated. Not sure if the PSV is normally open or normally closed, but I don't see how it would make a difference either way - the vapor will always have an available flow path out of the tank and into the canister via the checkvalve on top of fuel tank.

I don't have any experience calibrating a "purge" event so I'm not sure how sophisticated the control strategy needs to be. Pretty sure you don't want to purge at idle and obviously not under boost. I think you'd want to do it when the engine has a bit of (but not a lot of) vacuum, and some decent engine speed so the disruption of burning off the swill in the canister doesn't disrupt the engine. I remember from my OBD calibration days that poorly implemented purge control can cause a herky-jerky feeling for the driver - but I never calibrated purge stuff so I'm no expert.


I think I could replace the existing CCV with a checkvalve to allow fresh air into the system (but no vapors could escape), and then repurpose the CCV as the new EVAP valve. The existing EVAP valve is a simple on/off valve so it can't be duty cycle controlled like the CCV can. This seems like it'd allow me to use a PWM output on the new ecu to throttle the purge flow as required. I don't really know if using tank vapor pressure as an input to the ecu would help tailor the control strategy. Also don't know how large or small the operating range is where there are suitable conditions for effective purging.

Maybe I could enable purge ONLY during a decel fuel cut and get a little "crackle" like all the cool people are doing these days?

Maybe I'm overthinking it and a simple on/off valve set to come on at steady-throttle, over 50mph and between 75 and 80kPa MAP would work just fine?

If anyone has experience with rigging EVAP purge setups to clear out the canister without causing the engine to run weird - I'm all ears.
 

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Maybe I'm overthinking it and a simple on/off valve set to come on at steady-throttle, over 50mph and between 75 and 80kPa MAP would work just fine?
Honestly, I think the ecu just opens the vent at a certain pressure. I'm not sure rpm would matter too much as the charcoal canister is supposed to clean off anything flammable. If it was me I'd get rid of the PSV and replace the CCV with a check valve and I'm not sure if there is any difference between the vent line and evap line from the tank to the charcoal filter.
 

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Thank you Hodgdon Extreme for starting this thread. I have the Panic Made Link and am in the process of running through this as well. My harness accommodates the PSV but not the CCV (no direct wire run although I do have another generic analog connection available). The simplicity of the check valve would be ideal for me so I will be following this thread closely. Before this post the evap system was a bit of a black box.
 

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Evap purge solenoids are often most active at idle. Ever heard very fast clicking not near injectors? That’s the purge valve being controlled off and on very quickly.

Gonna be completely honest here. I did not take the time to read every little detail but I’d say if there is a way to simply control the purge valve via PWM controlled output from your ECU, then Have the TANK pressure sensor be your trigger (input) to allow the purge valve to be opened.

You probably already mentioned this but that’s what I would do. This would probably require you to reroute some EVAP lines but shouldn’t be too hard to do and it would be very simple.
 

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hey guys, sry dont have really time at the moment to read everything but here is how i did it.
you do not want to have it in idle or when the engine is cold. it has to be activated when cruising off boost.
you will have a noticable enrichment from it if youre activating it in open loop!
i also added a >10kmh condition, but you dont need it. its just pretty loud and annoying when im playing with the throttle manually when standing in front of the engine

edit: didnt use a checkvalve for the ccv, just wired it parallel with the VSV
 

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Discussion Starter · #11 ·
edit: didnt use a checkvalve for the ccv, just wired it parallel with the VSV
Thanks for response. If I understand you correctly, you wired the CCV and VSV in parallel so that both open/close simultaneously based on the same control output of the ecu.

Are you controlling them via duty cycle as a PWM device?

My understanding is the VSV is not meant to be controlled that way (but I could be wrong) but the CCV can. Thus, the idea of replacing the CCV with a checkvalve was so I could re-purpose the CCV as the new VSV...enabling duty cycle PWM control of the purge event.
 

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yes i do as you can see in the screenshot. I wont say im 100% correct, but i cant really imagine it being an I/O valve. OEMs always program it to open gradually dependent on RPM when the engine is warmed up and in closed loop. obviously only in off boost scenarios. dont underestimate the amount of fumes coming out of it. as i said, you can noticably see the enrichment in AFR. if you just opened the valve 100% at low MAP you would see reeeally large enrichment.
in fact the CCV could operate like an I/O valve because its sole purpose is letting filtered air to pass the system when needed, and preventing gas fumes from exiting when not purging.
 

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Discussion Starter · #13 ·
yes i do as you can see in the screenshot. I wont say im 100% correct, but i cant really imagine it being an I/O valve. OEMs always program it to open gradually dependent on RPM when the engine is warmed up and in closed loop. obviously only in off boost scenarios. dont underestimate the amount of fumes coming out of it. as i said, you can noticably see the enrichment in AFR. if you just opened the valve 100% at low MAP you would see reeeally large enrichment.
in fact the CCV could operate like an I/O valve because its sole purpose is letting filtered air to pass the system when needed, and preventing gas fumes from exiting when not purging.
Again thanks for the reply.

Because the CCV is definitely a PWM device - the VSV doesn't need to be. By opening the VSV, the CCV can be throttled via PWM to control the actual purge flowrate out of the canister and into the intake. Put another way, there is no need for both CCV and VSV to be PWM devices - which makes them more expensive to build - and more hardware/software intensive for the ecu to control. In terms of OEMs, that makes a difference.

Anyway, not arguing with your arrangement - just explaining my thought process. Sounds like it's working nicely for you and I greatly appreciate the feedback!
 

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i had a look at the diagram and if you look at the CCV and VSV(EVAP) you can see they use the same PWM type solenoid symbol, different to the VSV for vapor pressure.
(or maybe there was just a misunderstanding - im talking about the EVAP VSV at the manifold)
earlier models didnt have the CCV, instead a check valve. the reason they replaced it with a CCV is, so the system can close the CCV and open the VSV in order to check the system for leaks.
im still assuming both are PWM type and that the VSV is controlling the amount of gases being sucked. if you would control purge amount with the CCV you would build up negative pressure inside the whole system.
also i dont think that there is any price difference between I/O and PWM valves, both are just coils driven by transistors.
anyway, i like that somebody cares about it and doesnt just unplug everything. less smell - less fuel consumption.
🍻
 
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