Horrible Gas Milage
 

So, i have a 1997 chevy blazer 4dr i have been recently been getting really bad gas milage (15 city/ 18 high way). I get an EGR valve code sometimes when its really cold (below 10 degrees F) but other than that, no problems. It still idles just fine and accelerates just fine. Would the EGR problem really be causing that much of an issue??

(note: Theres 70k on this baby)

I think 15/18 is pretty normal. That's exactly what I get in my 2001 Jimmy.

ALTHOUGH, the 2000 Blazer I had before this one, would regularly get 22 HWY, and I even got 24 HWY on one trip. I have no idea what could cause the discrepancy, though.

gassers get bad mileage when its cold out. I got 25.5mpg in my '96 4dr driving through Ohio last summer when it was about 78 degrees at 62mph on the expressway. With my daily 72 mile commute to/from work, I have been getting like 17mpg tops even though I do 65mph and 90% of it is expressway.

I spoke to a rep at O'Rilley about the same problems with my 97 Blazer. I was going to change out the O2 sensor and was pricing them when he asked why I was changing. I explained about the lousy milage and he asked two very simple questions. What plugs am I using and how old is my air filter. Well, I changed plugs after I bought the truck about 4 years ago to Bosch Platinum and havent changed the air filter but once. His recommendation.... ONLY USE AC DELCO plugs and get more air in. Recommends a K&N air filter. Seems the platinum plugs from ANY other brand will corrode away in no time due the the temps run in the combustion chamber. That included Bosch, Split Fire etc. Also an increase in air flow helps the spark burn more efficently. The two combined, better milage by 4 or 5 miles a gallon. Well, nothing confirmed yet, gonna make that this weekends project. However, I wonder if the axle ratio may be set for towing rather than my usual daily commuting. I am thinking about swapping rear ends for more economy and maybe even a cam swap.

That's about what I get, high 14's to mid 15's in the city and about 17-18 on the highway

Sounds about right to me too. My 5-speed gets about 16 city, 19 hwy, with the K&N filter and an unknown brand spark plugs.

Be careful on those oiled filters guys. If you drive in any dusty environments the K/N allows alot of dust through and this will slowly kill your engine. The oil will also clog up your MAF which will hurt your mpgs. I'd highly recommend you stick with a dry paper filter or Amsoil's new filter.

If you want better mileage, drive like a granny. On top of a new dry air filter and Delco plugs, clean you MAF sensor and put in a new fuel filter. And maybe clean your throttle body?

15/18 is completely normal, at least with most of the Blazer/Jimmys I've owned.
The exception? The 2000 Blazer I had last year, would get 22mpg on the highway. It even got 24!!! on one trip. I'm not sure HOW it was able to get such good mileage. But I hated those cloth seats, so I sold it. My mistake!

I also get 15/18. I tried using higher grade gas and it helped my mileage some but it wasnt worth paying extra for.

Boy you said it about K&N Filters. I proved your point on a Dodge Dakota 4x4 4.7. Running a K&N in 30,000 miles I pulled the air box to change plugs & I could not believe all the dirty & crap in my Air Box & Throttle Body. Went back to stock dry filters & the next 30 found the Air Box & Throttle Body clean.
USE ONLY AC DELCO PLATINUM PLUGS in your 4.3.
Our Blazer 4x4 has 3:73 gears & in the winter we get 16-18. In the summer I have got up to 24 mpg on the freeway running steady on cruise. But we get an avg of around 17.5 overall.