very bad gas mileage

Asked by Jan 09, 2011 at 08:03 PM about the 2003 Chevrolet Blazer LS 4-Door 4WD

Question type: Maintenance & Repair

I have owned my Blazer for almost two years, just had a major tune-up, replaced wires & plugs w/double platinum, rotor and cap, fuel and air filter.  Gas mileage went from 16mpg to just over 12mpg.  It runs smoothly, has good pick up, idles a little rough as it always has.  The mechanic said it was in bad need of a tune-up as he inspected parts removed.  I thought for sure it would increase the mpg, not decrease.  The cost at the gas pump is killing me!

11 Answers


I have the exact problem did major tuneup with all parts replaced as anniegirl replace and getting 12 miles to the gallon now also. Anyone have any ideas?

23 people found this helpful.

is it possible that your fuel injectors could be leaking also may want to check to make sure you have proper tire pressure

5 people found this helpful.

possibly could have sometihng to do with the winter gas mixtures. ive lost about 3 mpg because of that.

3 people found this helpful.

it could have the same problem mine has .i have a 94 blazer and just posted a question about my injectors spraying to much fuel and now its just flooding out with out starting at all.when its running does the exhaust smell really rich of fuel ?

5 people found this helpful.

my nieghbor has a 97 blazer he recomends k&n air filter with a pick up of bout 3-4 mpg....and he averages around 16...hope to help..

3 people found this helpful.

Check all vacuum lines, and re-check all of the plug gaps. I would also recommend using this type of gapper. Much more acurate and less chance of damaging the plug while gapping.

2 people found this helpful.

my 94 did the same thing, the spider under the intake was bad. @ 1st, it wasnt, the longer it went, the more i could smell gas.

2 people found this helpful.

Hi if your idle is a little rough after checking leads and plugs try checking the EGR valve just behind the thomastat on top at the front of the engine some times they can get a bit of carbon in them and they dont shut off completley ,,or they can just not work ,,we live in the hills in NZ and after tweeking everything I can the best I can get is 17 mpg US ,,these are a heavy little vehicle and could of used a V8,,,

6 people found this helpful.

These Chevy engines suffer from a leaky intake manifold gasket on the from driver's side corner. I redid mine and gas mileage finally went way up! Check for vacuum leaks too. Very important.

7 people found this helpful.

also the temp sensor it acks as a choke an also the number 17 wire comming of the ecm mine went from 18miles to 6 miles replaced temp sensor an know it back to 18

5 people found this helpful.

My gas mileage was horrible just before my transmission went out.

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