It could be because of the removed cat. I've noticed that my mileage has plummeted in the past few months, and I believe the cause is a plugged cat. With the non-restricted exhaust flow, your Blazer is probably getting great airflow from intake to exhaust. Proper combustion is all about the right mix of air and fuel; with no restrictions on the air flow in the exhaust, its allowed to take in more air with the mixture and further lean out the fuel. Its kind of like if you inhale deeply and only exhale half-way; if you restrict how much you exhale, you'll be limited on how much you're able to inhale. The more air in the mixture, the leaner the fuel burn. That will keep it on the lean side with the ability for the injection system to enrich where needed.

At least, thats my theory. Its illegal as hell, but I can see where removing the cat might increase fuel economy quite a bit. Out of curiosity, do you get a check engine light for the rear O2 sensor being removed?

 

It was mid year 2002 they removed the EGR valve etc.

 

Nope no cel for the rear o2 sensor

 

what was the reason for this? Did it end up being a good thing? I spend like a half hour looking for my egr one day then looked online and found out I dont have one. I told my autshop teacher they got rid of them in 02 and he told me I was wrong and every car on the road has an egr valve. Then I brought in my truck and had him look at it and he was like damn your right, thats weird lol

 

So, I had a 97 and was lucky to get 16-17 out of it. I've now got a 2000 ZR2, and 16mpg is a good day. Can removing the cat. really be that big of a help? I ask because I'll totally do it to my ZR2 if it helps that much. I would love if we could track down the reason for your great gas mileage, because I bet people on here would like to try it out for themselves.

 

Lol tell him a dog told ya so!
Seriously Swartlkk (Kyle, our admin) posted that bit of info in a thread I had read after I looked for 20 mins or so & couldn't find my EGR a few years back.
I'm not sure of the reason but I could guess if they could do away with the EGR or find another way of using return exhaust gasses, or manipulating them its place & there would be less issues - why the hell not?!

 

My old 96 always got 24 to 26 on a long trip so i wouldn't worry to much.

 

I have my pre cat removed, original cat is replaced with a high flow & my down stream 02 sensor has been made defunct in the way the PCM reads it. They put a "J clip" in the PCM in a way, just reprogrammed it that way.
See my sig about Wolf.
Now granted mine is not a normal ride, emissions, exhaust (sorta, just a single in/dual out but a free flow muffler - look in one end & straight out the other), fuel delivery etc so it's hard to say from my experiences.
You should do searches for cat removal, 02 sensor, downstream, best mileage... change up the wording & search around. You'll find lots on the subject of better mileage.

Not my intention to the OP but just some info about mods & mileage is all.

 

ya its been awhile since I've been on this forum. I've dabbled with Camaros too much and been on thirdgen.org most of the time.

But ya, I'm not even talking highway at all. Most of my driving is city. When we removed the cat on a friend's 99 k1500, it didn't do anything to mileage at all. My friend has a 99 blazer with no cat also, and he only gets about sixteen, I've been with him when he clocked it. I've literally looked at every angle and I can't think of anything it could be. Do I just have a really light foot?

When I first got the rig, it had a really dirty MAF sensor and I cleaned it and went around on a bunch of WOT runs for about thirty miles to make sure the trans was shifting normal again. I did the math and at WOT I was getting 18. Literally, that's all I was doing was complete pedal to the metal. Could the PO have done some really drastic mod that's hard to see or something? This can't just be the cat.

Today I drove six miles, never over twenty five, clocked it at the pump at 19...

 

My friends 96 got really good mileage and i never understood how because he drove it like it was stolen all the time and it had 210,000 miles on it!!

i just filled up today and got about 17 with about 80% of my driving under 40mph.

Maybe GM had a deal with the gas companies and some blazers got made without the "gas hog" option installed lol