I keep throwing a p0455 code, for large evap leak
on my 1997 1.5 with 130K
of course I replaced the gas cap, but that wasn't it
the leak is larger
intelli fix, is recommending the canister drain cut valve....
I've pulled the fender liner a couple of times and inspected all of the lines and connections
I've also lightly pressurized the gas tank (7-8 psi) and sprayed soapy water on all of the lines and connections
none of the connections are leaking
some of the 1 way valves show soap bubbles
I'm not certain though of the working steps of the 3 different one way valves and two different electrical connections in the system
I realize it could actually be a failed pressure sensor with no leak really existing....
does anyone have a laymans explanation (pictures?) of the evap system in the back of the car/tank.
I will then need to next move to the front/engine bay part of the system also
but so far nothing visually stands out.
any help appreciated
thanks in advance everyone!
brant

 

smoke test the EVAP system to find out what is leaking, shouldn't cost much at a independent mechanic shop to do.

 

The evap syatem consists of a vent valve ( as fuel is removed from the tank the pcm opens the vent valve to replace the fuel that is removed to keep the tank from imploding)
A purge valve ( this valve opens to the charcoal cannister to expel excess pressure so the tank does not expand and burst)
A pressure sensor ( the sensor mounts on top of the tank and reports pressure to the PCM)
The purge valve vents to the intake so that fuel vapors are burned
The system is a low pressure system, never more than 1 psi. More than likely you have a vent valve stuck open. Vent valves suck in outside air and over time suck in dirt/dust which causes them to stick. A bad purge valve generally sets a code specific to the purge valve. If you put 7-8 psi on the evap system you will likely cause a leak.

 

hixx,

thank you a ton
this is exactly what I was hoping to learn
and thank you for explaining the different roles and components.

do you know where the vent valve is located specifically?
(I will start testing components and begin with this one)

also do you know if there is an OHM test value or other means to assess the pressure sensor?

thank you again for your time
brant

 

Mazda calls it a tank pressure control valve on that model/year. If you google that and click images you should find a complete diagram of the system. Once you see what the valve looks like you will find it easily. The pressure sensor is almost foolproof and will set a code if it goes bad. Testing of the vent valve is a bit involved as it requires a vacuum pump and ohm meter. Generally you should be able to apply 12 volts to it and it will open and close. You can blow air through it in one position and not in the other position. Good luck

 

After thinking about it for a minute that valve should be closed with no power to it. So remove it and try to blow through it. If you can it is bad. When you get it off bang it on something and see if dirt comes out.

 

hixx: thanks a ton, this is a very useful explanation!

 

Mazda Protege Workshop Manuals


Look down the table of contents and check out Section 01-16 Emissions ... click on 01-16 and it takes you to the EVAP pdf