08' silverado, 12mpg??

[skeeter123]

Get a scanner that can show you "live data", and check the LTFT long-term fuel trim. If its high (~> 4% or so) the PCM is deciding to enrich the mixture for some reason, possibly ECT / O2 sensor problem / vacuum leaks.

Oh, and the scanner should tell you if it's running in open-loop or closed-loop mode. Open loop is usually when engine is cold, before O2 sensors start working; PCM enriches mixture till engine warms up. If it doesn't get into closed-loop mode, it's like running with the choke on all the time.

Also, do you smell gas at all? maybe it's just leaking out somewhere between fuel tank and injectors. You could also check fuel pressure to see if it's within spec.
Hope this helps.

ps check out:
http://www.automotiveforums.com/vbul...&highlight=ect

http://www.asashop.org/autoinc/may98/techtotech.htm

[ukrkoz]

27mpg hwy? on 5.3L? window sticker? was it handwritten? stop torturing yourself and your car, it's right mpg for it. best is 20 for 2wd, hwy; average is 11-15 mpg, depends on model.

27 mpg.... just shaking my head....

http://www.fueleconomy.gov/feg/bymod...ilverado.shtml

sorry, i have 2000 5.3 vortec, no active management or things of that nature. 17 average regular driving, 22 straight hwy. you did not know mpg IS NOT getting better?

[Elbert]

I get approx 14 mpg on hwy with 07 K2500HD with 6.0. You should be getting better than that with the 5.3. Assume no check engine light is on, clean air filter ...nothing obviously wrong. I would be tempted to change the 02 sensors but they can be expensive. I would order from Rock Auto or other place (over the dealer).

[someday31]

Originally Posted by j cAT

I would replace the plugs at 50,ooomi. check all for proper color . If color off check compression.


replace the ECT sensor not expensive or hard to do.

your fuel 87 octane shell is what I use . I get with my 2000 5.3L 19 MPG in the summer ...you should get 22 MPG..

you have a problem with this 12 MPG ..

I also use techron injector cleaner ONE 16 OZ bottle /tank .I at this time add 3-4 OZ of marvel mystery oil to fuel ..this all cleans and lubes the entire fuel system. replacing the fuel filter at the 30-40,000mi mark is also a good idea..

INjectors may be sticking dirty etc..

I have an '03 with 5.3 extended cab/short bed.....I consistently get 14.5mpg no matter how I drive, Im not heavy on the pedal....plugs are iridium with about 40,000 miles on them, been getting this mpg for a few years....thought I use to get 16 or so....

[j cAT]

Originally Posted by someday31

I have an '03 with 5.3 extended cab/short bed.....I consistently get 14.5mpg no matter how I drive, Im not heavy on the pedal....plugs are iridium with about 40,000 miles on them, been getting this mpg for a few years....thought I use to get 16 or so....

2003 5.3L should get around 16mpg ave. driving. with the 4wd.1500 truck..lower than this may be the O2 sensors or the MAF needs cleaning with CRC MAF cleaner..

also clean the throttle body and IAC at this time with throttlebody cleaner [no carb cleaner ! ]........

these items control fuel mixture..

injectors dirty leaking will reduce MPG ...........