Havent really drove the blaze in a while because of the service light has been on. Not very long ago I switched from the stock gas cap to a locking cap. Sometime later my service light came on, I went to autozone and they pulled the code (Cant remember exact one) but they told me it was the gas cap. I told them I replaced it and they told me to spray the cap with wd-40 to "soak the seal." Did that and the code went away, some time after that the code came up again. This time I went to a family mechanic, and what I was told was that the problem was that the "fuel purge valve" and needed replace. I havent ever heard of this so I was wondering what you guys think. I would rather deal with the problem myself because I feel as if our mechanic is kind of shady.

 

try putting back the stock gas cap to see if the problem goes away. you can get a new one at the dealer or used at the junkyards.........

 

Yeah I tried that and it yielded the same results, the light still on..

 

You can only use a GM stock gas cap to solve this problem. This is a problem in all new vehicles. Use only GM stock parts for your Blazer. all others will fail eventually

 

I put the stock one back though like I said, but the lights still on.

 

Your stock one may have an issue with it causing you to still get that light. You'd be better off trying a new one. Keep the package and receipt though just in case it doesn't work.

Also, the WD-40 probably didn't last because WD-40 evaporates pretty quick.

 

The WD-40 trick will cause the rubber seal to swell a bit allowing it to seal better. It will also cause the seal to degrade quicker.

Your problem is likely the vent solenoid which is located under the back of the truck just ahead of the rear axle either near the frame or on the back of the gas tank (depending on 4wd or 2wd). If you had the specific code, you could run a search. I cannot remember exactly what the code is (something like P0440 or P0442 comes to mind), but I do remember a good discussion on the causes.