I have an 03 silverado stock 5.3 i went from apprx 400-450 miles to a tank to 200 miles a tank and i have no codes and engine seems to run fine not missing? Any ideas on what this could be? Thanks for the help im new to this site lots of great info here. Thanks again

 

someones stealing your gas... but seriously thats pretty bad mileage

 

check for the hole in the gas tank. its leaking out somewhere ?

i dont know

 

Try this...

Clean MAF with CRC maf cleaner.
Clean airfilter
check Fuel filter
Plug wires

....pray

 

If the above don't work re-place your O2 sensors. I had some bad ones on a 5.0 Mustang, and I got close 5 city 3 Highway back.

Hell even just check to see if there damaged while you check the above.

 

I would surely check for a leak..
and do all of the above and let us know what happens..

have you started using Fuel with Ethanol?i know that will kill your mileage pretty good, but i dont know about that bad..

 

Good luck! Mine is getting 2-3 mpg less recently. I cleaned the air cleaner; also the TB and MAF wires with CRC tb cleaner about 100 miles ago.

 

Get rid of those 35's and that lift and drop a LQ4 in it .

 

thats some bad mileage thank god i never gotten that bad

 

Cleaned MAF alot better now. Didnt know it could make that big of a diffrence. Thanks again