Jonathan_ed3

To make a long story short, I'm interested in having an operational EVAP system (in that it will vent fuel tank pressure and vapor), but without all the self-testing and diagnostic that normally occurs.

To this end, I'm curious as to which sensors/valves/solenoids are merely for TESTING and which are actually operationally imperative to digesting fuel vapors through the engine.

Everything in bold is using Honda's nomenclature.

Evap Canister Purge Valve - This valve is electronically operated, and normally closed. This is in the engine compartment and as far as I can gather, the only "evap" component not in the rear of the vehicle. When commanded by the PCM under certain conditions (coolant temp above 149* F for instance), will open to allow the fuel vapors stored in the EVAP canister to be pulled via vacuum through the intake to be burned off. This is controlled via PCM pin A6 and it says that it's "duty controlled" via PCM
* The purge valve will for sure be required.

Evap Two Way Valve - From what I can gather, this valve is purely mechanical (no electronic control). Can anybody confirm? When the vapor pressure in the fuel tank is higher than a certain value, the valve opens and feeds fuel vapor to be stored in the EVAP canister.
* This valve will be required, just cannot confirm if it's purely mechanical or if the PCM controls it at all with feedback from the fuel tank pressure sensor

Fuel Tank Vapor Control Valve - Is this valve also purely mechanical? This valve specifically relates to refueling. It's supposed to open with the pressure in the fuel tank, and also feeds fuel vapor to the EVAP canister.
* It seems like this valve will also be required, especially to aid in refueling. Again, just cannot determine if it's purely mechanical or if it also relies on feedback from the fuel tank pressure sensor

Evap Canister Vent Shut Valve - I cannot find much info on this valve. Generic web searches suggest that for most manufacturers, this valve is normally open. Honda FSM says this valve has battery voltage via PCM A4 (lt grn/wht wire) at ignition switch on. The other wire in the vent shut valve's connector is black/yellow, originating at fuse 6, which is hot in on.

• I don't understand this....how can it have power on both sides of the connector for this valve? One directly from the fuse box on blk/yellow wire, and the other from PCM pin A4.
• Does this mean that this valve is normally open? If so, under what conditions would it close? Does it close only for diagnostic self leak testing?

Evap Bypass Solenoid Valve - I cannot determine what exactly this does. When I search for it in our repair database at work, it returns no results. I see that it is controled via PCM A3, and also, like the other evap sensors, has battery voltage at ignition on.

• What does this thing do?
• Is it required for Evap function or is it just for testing itself?

How can the 3 items that are directly controlled by the PCM (Evap Bypass Solenoid Valve, Evap Canister Vent Shut Valve, and Evap Canister Purge Valve) have battery voltage at both terminals on the connector? 1 from blk/yellow at fuse box and 1 from the PCM?

What role does the Fuel Pressure Sensor play in overall Evap operation? When searching for detailed information on it, I cannot find much on it. I see it's a 3 pin connector.

• I found that with the ignition switch on and fuel fill cap open, you should see about 2.5v @ PCM A29. Light green wire on FPS
• Looking at the diagram, it appears that the Green wire on the FPS splices into the green/yellow wire at the TPS and then goes to PCM C18, which also goes to green on the air pump current sensor.
• yellow/blue from FPS merges with air pump wiring, with VSS, and with TPS and originates at PCM C28

Looking at how the FPS ties into the VSS and TPS, I'd imagine the PCM calculates a certain speed and throttle position in which to dump pressure/vapor into the motor? Is this accurate? Does anybody know what the exact demand conditions are?

Please only reply if you're familiar with evap systems or can contribute to the thread. I don't want to hear about how you ripped yours out and "everything is fine".

Thanks in advance to anyone that can help me out with this

Even Glemmestad

*revive* did you ever find out any more details about this? I’m looking to understand the functions of the EVAP system better myself. Thanks.