my wifes 99 blazer has started getting really bad fuel mileage.about 7.8 to 8.5 it fluctuates.she uses it to deliver mail and she used to get 11.5. heres the list of things i tried so far.new fuel filter,new cap and rotor plugs and wires.plugs looked clean no evidence of running rich.it runs great.heres one thing i dont know if it would affect it.in the hot summer 85 degrees and up once in a while it will throw a po452 evap emmissions control system pressure sensor/switch low input.if you pop the gas cap or let it sit overnite it goes away.its done this since new fuel pump but gas mileage just started going downhill this year.like i said it runs great.checked for fuel leaks.really lost on this one any help would be appreciated.thanks in advance

 

Were you able to find a solution to your decrease in mpg? I have a similiar problem with my 99 after replacing the fp.

 

I ran some sea foam through it every month.half bottle to a tank of gas.it helps but not a real good answer.

 

I've put it on a scanner and drove it everything checks out normal.

 

If your scanner can show live data, check the fuel trims. That will let you know if it's actually running rich, or what.

Maybe you've got an O2 sensor or two getting lazy, but not bad enough to throw a code?

Heck, maybe they're sneaking in more ethanol into your fuel! That won't help mileage any,lol!

 

yes it was a live scanner.everything was in specs.local garage ran it for me while I was there

 

how are the injectors?

 

been in there for 150,000 miles

 

might be time to check them out