Thank you for clarifying the operation of the EVAP canister. I assumed that's how it worked but I have assumed wrong before.


This is the vent valve air filter tech2 was referring to. A clogged air filter may explain another mystery that has plagued me for years.


The fuel tank pressure is monitored by the PCM. Mode $06 test $45 $02 will fail
if the tank vacuum ever reaches 20" of H2O. I never really understood why but
the possibilty of a clogged vent filter may be the reason the test exists. The purge
valve pulls fuel vapors from the EVAP canister during normal driving. No vaccum
is produced because the vent valve is normally open. But if the vent filter were
plugged up, the engine could inadvertently pull enough vacuum to collapse
the fuel tank. By monitoring the tank pressure, the PCM could close the purge
valve if the fuel tank vacuum ever got dangerously high.

 

Here's how to test the fuel pressure sensor after it is removed from the fuel tank.

 

An online converter shows that 6.6 kPa is only about 1 psi.
One psi seems like a trivial amount of pressure until you realize the force generated by that pressure is detemined by the area it works on.
My Tracker has a 17.4 gallon fuel tank.
One gallon = 231 cubic inches.
So my tank volume is = 4,019 cubic inches.
To make the math easy, assume the shape of my tank is a perfect cube.
The length of one side is the cube root of the total volume (4,019).
So length of one edge is approximately 16 inches.
The total area of the cube is six times the area of one side.
The area of one side is 16 squared or 256 square inches.
The total area is six times that or 1,536 square inches.
Force is equal to pressure times area.
So the force = 1 psi times 1,536 square inches.
That means a tank vacuum of one psi produces a crushing force of nearly 1,500 pounds.
That's 3/4 of ton.

 

Update.

My 1999 Tracker doesn't have the filter that L84sky referenced.

Live data for my Tracker shows the fuel tank pressure is too high. It's running at approximately 14mm Hg and the standard is -32mm to 10mm Hg.

Any idea what is causing this?

 

I see that now. The 1999 EVAP system is significantly different from 2001.


On my 2001 my first guess would be the vent valve stuck closed but I cannot find a vent valve on a 1999 four cylinder. High tank pressure usually occurs because the tank is not vented on a warm day. While observing tank pressure on live date, removed the fuel filler cap. If the pressure reading does not drop to atmospheric you have a bad pressure sensor. If the pressure does drop, rerun the test but this time pry the hose off the EVAP canister coming from the tank. If the pressure drops to atmospheric again you might have a clogged EVAP canister.

 

Update on this thread:

I'm still dealing with high fuel tank pressure.

1) I removed the fuel cap while observing the tank pressure on live data and the pressure dropped to zero. This leads me to believe the fuel pressure sensor is good.

2) I removed the hose from the EVAP canister coming from the tank. The pressure did not drop at all.

3) I removed the inline pressure relief valve (next component in the line running from the EVAP canister to the fuel tank) and the pressure dropped to zero. I took a picture of the part in question. The long hose runs to the EVAP canister, the short one to the fuel tank.

Three questions:

1) Is there a vacuum line that hooks up to the port on the top of this?

2) Is there a function test for this? I blew through it from the tank side and air did pass through. There was a buildup of pressure before the valve opened and the air passed through.

3) My concern is that I'm missing a vacuum line and that is why this valve is not engaging to depressurize my fuel tank...or is it just designed to work without any vacuum input once the pressure from the tank builds to a sufficient pressure?

 

My 2001 V6 does not have the part pictured above. As a test, can you purchase the same length of plain tubing and install it in place of the assembly shown above? If your pressure problem goes away maybe that pressure relief valve is faulty or should not be there in the first place. In my mind a pressure relief valve should not be in series with the tank and the EVAP canister. It should vent tank pressure to the outside air.

 

L84sky thanks for your help. I did order the part (it’s very common and easy to get.)

I’ll post an update once I get the part installed.

 

Is there a link to a parts diagram showing how it fits in the system? I'd like to study it if possible.