Alright now that I can post again, here is the problem I am trying to diagnoise. I have been getting the SES light and when I scan it I get two P0420 codes. Which I know is a "Catalyst System Efficiency Below Threshold (Bank 1)" code generically. I have run a google search on this code and gotten lots of info about other vehicles and some solutions that worked on other cars.

Here are some more detailed symptoms of the truck. Just 5 weeks ago I drove home on the highways doing 65-67 mph and got 22mpg, now doing all highway like that trip I get nothing better than 17 and sometimes near 15mpg (this is all calculated by tank of gas with nearly all the same constants [tire pressure, speed, cruise, weather conditions]). After having driven aways on the highway (20+ miles) I slow down as I exit the highway, stop at the light, then when I go to accelerate the SES light comes on resulting in the P0420 codes. It generally only happens like this after warming up all the way, slowing down for something, and then speeding up. I have a handheld OBD2 scanner and have cleared the code many times and it keeps coming back the same way.

See next post for more info, as I am trying to bypass the currently limited post length system

 

My thought on this from the research I have done is a faulty upstream O2 sensor, a badCat., a leak in the manifolds or somewhere in the exhaust (everything is original with 141k miles). I have recently been getting a louder exhaust sound from a broken down muffler which I will be replacing shortly (see other thread). I am wondering if this might have an affect on the code being called.

So my questions are:
1) I was wondering if anyone had ever survived this code with the Blazer, without spending too much money?
2) What would be the best approach from the above details in solving this problem?
3) Any other thoughts on the subject? I am just a college student and am trying to save as much money as possible.
Sorry for the long post, thanks for the help in advance!

 

As the thread title and one reference in your first post state P0420, I will assume that the P0240 reference is a typo.

Don't know if you saw this or not, but I have a P0420 Explained post in the DIY section which runs down the list of causes for this problem. I did have to fix the post so it is complete, so it is all there now.

 

Yes I meant the P0420 code, thanks for the link and completing the post, I had not seen that when I ran my search. The forum bugs probably made me skip right over it. Thanks.