Things to check for low mpg

[Brians4x4]

I have a 2005 5.3 and have gotten around 14-15mpg in town since new. Recently I've been getting around 7.5-8mpg. I have no check engine light and am wondering what I can check. I had a bad injector on another vehicle that caused a severe change in mpg but it was blowing loads of smoke out the exhaust.

Thanks.

 

[Scottydoggs]

could be tune up time.

 

[swathdiver]

Plugs, wires, parking brake shoes, brake pads, rear drums hangning if you have them, fuel trims messed up, O2 sensors, stuck open thermostat, crummy fuel, winter fuel, etc. etc. etc.

Have any trouble codes? Access to a good scan tool to monitor various engine functions?

 

[6speedblazer]

to be that low i would check the fuel trims. get a scanner on it and see what the oxygen sensors are doing. sensors can get pretty "lazy" before they throw a code.

 

[Rocket Man]

Make sure you're not in boost too much of the time lol.

 

[BlueCollarTahoe]

if you figure it out im in the same boat with this 8 mpg ********. please let me know.

2004 5.3 v8 no CEL codes.

got a tune up 18 months ago with all ac delco stuff.

changed out the 02 sensors on driver side. was getting rough idle and misfires. fixed it.

had the computer reprogrammed. diagnostics said this is the issue not fuel injectors as there is no code and the numbers were all off on the scan due to old programming. waiting to see a couple tank fulls see if it worked.

what are normal fuel trims?

 

[Rocket Man]

I can't believe you guys are getting that kind of MPG; I just got 7.8 on my last tank and I have a cam, longtubes and a blower and I drive with a heavy foot all city driving. In boost half of the time.

 

[BlueCollarTahoe]

I can't believe you guys are getting that kind of MPG; I just got 7.8 on my last tank and I have a cam, longtubes and a blower and I drive with a heavy foot all city driving. In boost half of the time.

wtf is boost? lol all i got is like 75 lbs of accessories on the car so far everything else is stock. keep about 50 lbs of crap in the back without the last row in there.

 

[HiHoeSilver]

wtf is boost? lol all i got is like 75 lbs of accessories on the car so far everything else is stock. keep about 50 lbs of crap in the back without the last row in there.

His "Beast" be Whipplefied, yo.

 

[Rocket Man]

Yo.