GMC Repair: GMC Van Charcoal Canister, charcoal canister, gmc van

Question
I have a 190 GMC rally STX/G1500 5.7L that failed emmisions. FYI The Van has a new Motor. I sent the emmisions graph to a friend/Mechanic He thought the Van failed due to a small fuel leak. I have high HC but low CO. I spent some time looking fo a gas leak on the van and found nothing.  So I then thought that maybe a bad charcoale canister might have the same effect. I read some stuff including how to test it but it's not real clear or at least not to me. My canister has one line from the fuel tank and one going to the throttle body. I confimed the hose routing with the dealer. According to the instructions on how to test it. I should attach a hose to the inlet of the caister (the side with the fuel line attached) and try blowing through it. I did and air passed feely through it.  Accoring to the instruction this should not be true. The second test was to attach a vacum pump to the outlet ( The line going to the throttle body) and draw a vaccuum. Again, it fails because I'm  able to easily blow through the canister. I also read about a thermal or pressure switch. My vehical does not appear to have either one.  I'm therefore assuming the pressure switch is built into my canister. When I went to the dealer they were unable to confirm this. On the parts list for the van they had a pessure switch bu no diagrams of it's location. The dealer had one that I was able to look at. I can tell you that I currently do not have one on the van. It sas just a little plastic disk with a couple of hose fittings. This leads me to believe the pressure switch is built into the canister.

The questions I have are for one would this cause my vehical to fail emmisions?  Two, is this a valid test for the canister?  If my canister is bad could I just buy the pressure switch/valve and attach it to the outlet of the charcoale canister? There are two canisters on your parts list which one do I need.

Thanks


Answer
Are you absolutely POSITIVE that the NEW engine is the EXACT replacement for the OLD engine. ?.


You did NOT do the charcoal canister test correctly.

I have the tset procedure instructions and can e-mail them to you.

However, You would need to contact me at:


onlineautohelp@msn.com


so I can give you further information on e-mailing the procedure as there is no way to e-mail it on this website to you.

When you contact me, verify that your canister ONLY has TWO hoses.


autohelp