Autonerdz forums

I got my WPS and I had to start playing with it.
Could not do a cranking compression on this car but the next one will not  get away 

PRESTON wrote on Mar 29^th, 2013 at 9:32pm:

Evap? I got learn about that I think you mention in one post that you use a snap on universal fuel cap or something like that.

Erik_1940 wrote on Mar 29^th, 2013 at 3:51pm:

SWEET,  Have fun man.

  Erik, that's the same fuel tank adapter I use, except mines blue  .  The main reason I use the WPS for EVAP testing is it can show me the entire picture of what's going on in the system.  The image I'm attaching is from a Toyota while running the in bay EVAP test with the Modis.  If you have ever done this test while looking at the modis screen, it can be difficult to keep track of which valve is doing what and what the pressure was then changed to!  It gets murky, at least for me.  If using the WPS, you can "sync" from the purge or vent valve, or both.  This testing also works very well with Chrysler LDP systems.
  In the image, you can clearly see where the purge was commanded on with the vent open, the very first part where the pressure decreases, but not by much.  I like this part to tell me there isn't a large restriction of debris or a stuck closed EVAP vent valve.  There are codes that can be spit out on some of the earlier EVAP systems across the board that may say there is a Large leak, but in reality it is a large restriction before, say, the fuel tank pressure sensor.  Sure would be nice to see the huge decrease in pressure but no change on the FTP reading.  Of course, the WPS may need to actually be hooked to the EVAP test port in that instance.