1998V70 P0455 Evap System "Theory of Operation" and a few questions

[ttermyna]

To start: Tracking down a P0455 code (Evap large leak) on a 98 V70. I am posting the following info which I found on Vadis because it has been useful and it doesn't seem as though anybody else has posted a similar explanation of the system. I know its long but I spent hours reading posts in which "Replace the gas cap" was trotted out over and over. I have some questions which follow the excerpt:

ORVR components
-1. Canister purge (CP) valve
-2. EVAP canister
-3. Shut-off valve
-4. Air cleaner (ACL)
-5. Fuel tank pressure sensor
-6. ORVR valve
-7. Roll-over valve
-8. Control module Motronic 4.4

EVAP canister
Hydrocarbon vapor pressed out of the fuel tank is dealt with by the EVAP canister. To minimize pressure drop in the lines between the fuel tank and EVAP canister, the EVAP canister is located close to the fuel tank. The EVAP canister volume is 2.1 liters. A new type of carbon reduces pressure drop in the gas flowing through the EVAP canister.

ORVR valve
There is a combined float roll-over valve by the connector for the large EVAP line to the fuel tank (called the ORVR valve). As its name implies it has two functions.

-a roll-over function which closes the large EVAP line connector so that fuel cannot leak out if the car is on its side or roof.
-a float valve function which closes the large EVAP line connector when the fuel level reaches the valve when the fuel tank is full

Roll-over valve
A small EVAP line runs from the ORVR valve to a roll-over valve located as high as possible on the fuel tank. The roll-over valve ensures that the fuel tank can breath if the ORVR valve is closed when the car has been refueled.

Pressure sensor
The pressure sensor provides information about pressure in the fuel tank. The sensor is connected to a Y pipe from the ORVR valve.
The pressure sensor also obtains the fuel tank pressure via the roll-over valve if the ORVR valve is closed.

EVAP canister shut-off valve
The valve is located close to the EVAP canister. The valve is part of the leak diagnostic system and temporarily closes the EVAP canister fresh air intake during the diagnostic test.

Filter
The filter is located by the fuel filler pipe and is connected to the EVAP canister shut-off valve via a hose.

Canister purge (CP) valve
This valve controls the flow of fuel vapor and air from the EVAP canister to the engine. The valve is controlled by the engine control module (ECM).

EVAP line
The line between the EVAP canister and fuel tank has been replaced by a large 13.5 mm line.
This allows fuel vapor to move easily between the fuel tank and EVAP canister when the car is refueled.

Fuel tank filler cap
The fuel tank filler cap has a overpressure/vacuum valve.

Check valve
The check valve at the bottom of the filler pipe on cars with ORVR is the same as that on AWD cars.

System description
When refueling starts the check valve in the fuel tank opens. The fuel flow creates negative pressure at the top of the fuel filler pipe. This results in an air flow in the fuel filler pipe. It is important to have low resistance between the fuel tank and atmospheric pressure (via the EVAP canister shut-off valve filter) to stop fuel vapor escaping from the fuel filler pipe. The principle of the system is called a dynamic seal.
When the fuel tank is full the ORVR valve closes and the fuel tank pressure increases rapidly. This closes the check valve in the fuel tank, preventing fuel coming out of the filler pipe when the fuel pump pistol is shut off.
Fuel vapor in the fuel tank (together with air) reach the EVAP canister via the ORVR valve. Fuel vapor is absorbed by the carbon in the EVAP canister. If the ORVR valve is closed the fuel tank is vented via the roll-over valve.
When the canister purge (CP) valve is closed the fuel vapor remains in the EVAP canister.
When the engine control module (ECM) transmits an opening signal to the valve, a vacuum from the intake manifold or from the fresh air intake creates a flow through the EVAP canister. The EVAP canister is connected to the outside atmosphere via the canister shut-off filter which allows the flow to evacuate the EVAP canister.
The air flow through the EVAP canister removes stored fuel vapor which flow to the engine and enter the combustion process. The canister purge (CP) valve pulses rapidly when the car is being driven and is idling.


Diagnostics are carried out as follows:
The EVAP canister shut-off valve and canister purge (CP) valve are closed and the fuel tank system is now completely closed.
Pressure in the fuel tank should be stable. If pressure drops the canister purge (CP) valve is leaking.
The EVAP canister shut-off valve opens, the tank system is open. The canister purge (CP) valve is pulsed and because of the negative pressure in the intake manifold the engine starts to suck air through the EVAP canister. Because the EVAP canister shut-off valve is open the pressure in the fuel tank drops slowly. If the pressure in the fuel tank drops rapidly the EVAP canister shut-off valve is clogged.
The EVAP canister shut-off valve is closed, the canister purge (CP) valve continued to be pulsed, pressure in the fuel tank should drop rapidly. If pressure does not drop enough there is a large leakage in the fuel tank system. A diagnostic trouble code (DTC) will be stored.
The canister purge (CP) valve is closed, the EVAP canister shut-off valve is still closed, there is negative pressure in the fuel tank.
The negative pressure (A) in the fuel tank has stabilized, if pressure starts to increase too quickly, this indicates a small leakage in the system. A diagnostic trouble code (DTC) is stored.
The EVAP canister shut-off valve opens, the EVAP function is enabled and the diagnostic test is finished.
To carry out the diagnostic:

-engine coolant temperature (ECT) is between -10OC and +107OC.
-no permanent faults stored.
-engine idling.
-speed must be 0 km/h.
-the concentration of fuel vapor in the canister must not be too high.
-there must be more than 11 liters of fuel in the tank
-the pressure in the fuel tank must not be too high.
-fuel trim must be active.
-the car must be below 2700 meters above sea level.

The diagnostic test starts at the earliest 17 minutes after the engine has been started when all conditions have been met. It takes approximately 30 seconds.

My Questions
Today I tested the Evap system with a helper and compressed air. I found a leaking hose connection which was repaired. I also noticed the following:

- The ORVR valve (near the fuel filter) will allow air towards the tank, but not forward towards the charcoal canister.
- The Evap line on top of the tank next to the fuel line will not allow air forward to the charcoal canister. Air flows freely from the end of the hose behind the ORVR valve back to the tank.

Shouldn't the flow be reversed? I know the test procedure calls for vacuum and not pressure so maybe that's where I'm confusing things.

Also I haven't checked the canister shut off valve for proper operation. On my 98 wagon the canister is in front of the drivers side wheel well. Should the valve be directly above the canister or do I really need to pull the whole fender liner off to get to it?

Any relevant input is appreciated.

[Ozark Lee]

The purge valve is located on the fan shroud, towards the left hand side of the car. There isn't a valve at the cannister itself.

...Lee

[ttermyna]

Lee,
Here is the diagram that went with the system overview above. It's showing a canister shut off valve at the "Air" line (large hose going to canister).

evap.jpg (133.46 KiB) Viewed 8572 times

The hose is routed over the wheel well liner, I don't see a valve looking up from the canister location. There was free flow both ways between the "Purge" and "Air" port on the canister. My thinking is if the shut off valve is stuck open, when the purge valve pulses it will not drop tank pressure rapidly enough and a large leak code will be triggered. I just don't want to tear the liner off if the shut off valve is supposed to be located nearby. Of course I don't see an electrical connector for the valve either. I guess I'll take the wheel liner off and see where that hose leads.

[Ozark Lee]

It will likely be easier to remove the cannister itself. I'm not sure how it is supposed to be secured from the factory but most of mine have been secured with a really big zip tye or a couple of real large diameter hose clamps.

I only have one car with the Motronic 4.4 system, the rest are either LH 3.2, Motronic 4.3, or the ME-7 systems and they have no such valve that I have ever seen. On the one car with the Motronic 4.4 I have never looked.

...Lee

[jimmy57]

orvr valve is part of the tank. Onboard Refueling Vapor Recovery means that when you fuel car the vapors are expelled via canister instead of backflow to filler neck. The backflow is controlled by the flap on tank end of filler neck.
The orvr valve is letting large volume vapor flow into low back pressure canister. But the orvr path needs to be sealed to assure no liquid fuel goes to canister so it seals via the float closing it when tank is almost full. The upper vent hose is small and the vapors will go out of tank as well as fuel showing in filler at that time. That is supposed to stop fueling.
If your fuel level is high when doing the checks the ORVR will test closed to canister but pressure pushed back into tank will pass with effort.
Large leak is detected when the pressure ramp down under vacuum applied is below target. Leaks can cause this but so can purge valve with low flow or lines with obstructions. Your car should have a filter below the purge valve and it could be obstructed. Pressure sensor line obstruction or the sensor itself can be the issue but less likely. Sensor can be checked by scan tool monitoring or voltage signal monitoring. If you use a screw driver to open the flap at gas cap end of filler and blow a vigorous burst at the filler it should register as a few kpa on scan tool or something on the order of 10-15 mV on the signal wire.

[ttermyna]

Jimmy,
Thank you for the troubleshooting info. I have attached a picture of the part which I mistook for the ORVR valve. It is next to the fuel filter. Any idea what this part is?

[ElGeorgito]

Very useful post!! Would it be possible for me to bypass the canister vent shut off valve? i think it is stuck in the closed position, and preventing the purge valve from doing its job. I dont really care if it can't do its diagnostic test.

[jimmy57]

If it is stuck closed or if the outlet is plugged by something then you'll have a lot of trouble fueling vehicle. The auto shut off of fuel nozzle will click off repeatedly.
WHat symptoms do you have leading you to think purge valve has low flow?

[ElGeorgito]

. The car has been a PITA to fuel for a while now. Pump always clicks off after a liter or so. I removed the canister vent valve this aft replaced it with a nylon elbow. The lead attached to the cvv showd 10 volts. The cvv was quite obviously in the closed position. I pulled the manifold side hose off the purge valve and it had tons of suction. Couldent get the other hose off due to some shrinkwrap hose connection stuff, but there was no hint of vacum at the now free flowing canister. The lead to the purge valve displayed 7-8 volts. hopefully it can purge freely now. I understand the purge valve only activates at certain times. I also went into the wheel well and the air cleaner on the fuel pipe is unobstructed.

Is there a way to test these solenoids on the bench? How much juice etc? Not really into the shotgun approach when buying parts. Hopefully something deep inside the tank is not to blame. Many thanks.

[misha]

Jimmy,
Thank you for the troubleshooting info. I have attached a picture of the part which I mistook for the ORVR valve. It is next to the fuel filter. Any idea what this part is?

That looks like roll over valve to me and it have a replacement clamp.Somebody allready have been in that area before.