Poor Gas Mileage 2002 5.3 Z71

XRMAN · January 30, 2012

I have a 2002 Z71 5.3 , 4l60,3.73, Power programmer,K&N 77 series w/power core filter. running 265/75/16 tires. Hooker Muffler single stock tailpipe. I can only get at best 13.6 MPG going back and forth to work, not a lot of stopping. During the summer that is not running A/C. Running 89 octane.

00Silverado4x4 · January 30, 2012

How many miles driven, how many stops, what kind of terrain, speeds driven, power programmer settings, tire size (stock?), tire psi?

Lots of factors that effect mileage.

I drive 8 miles to work one way but I have 4 stop lights, LOTS of "crazy" drivers, drive agressively & always use AC during summer so I don't even see 13.

Stevens03 · January 30, 2012

I'd look at the basics. First since your running K&N, clean your MAF sensor with a good electrical contact cleaner and make sure the filter is clean too. Next I'd look a the plugs and wires depending on mileage. Also for me on my 03, a transmission fluid swap to full synthectic gave it a solid 1-2 mpg better. I used Royal Purple Max ATF and saw a huge improvement all around.

Your muffler swap, did you recently do that? Depending on how much back pressure you lost, you could have lost mileage with that swap too. I know that on my 03, the Flowmaster I had (30-series, 50-series, and 40-series) all caused a loss of low end torque and loss of mileage. I installed a Magnaflow exhaust and got the mileage back. Just another thought.

Otherwise make sure your tire pressure is optimum otherwise that can cost you a few mpg too.

XRMAN · January 30, 2012

I don't have the K&N filter anymore when to Volant filter the pleeted paper filter,gained little low end under 2000 RPM. I do clean the M.A.F. on a regular basis, running maxi-flo Hooker muffler. I don't drive real aggressive either. I have close to 150,000 on the truck I bought it new. I am damn anal on changing fluids,tire pressure. I changed the plug wire couple yrs ago to Bosch,also changed plugs. I do stop a lot now you made a point of it.

Seems like the truck spark knocks bad and blows a lot of carbon clouds when I get into hard some times. I use Lucas injector cleaner also,I found this to be the best out on the market. I'm a Tech. by trade. Thanks for any in put if any more!

Stevens03 · January 30, 2012

I've heard very mixed results with using "non stock" plugs in GM motors. I've always had the best luck sticking with the Ac-Delco plugs. Its worth considering.

XRMAN · January 30, 2012

The funny thing is the truck came stock with NGK plugs....

Stevens03 · January 30, 2012

The funny thing is the truck came stock with NGK plugs....

Then thats what I'd put back in

00Silverado4x4 · January 30, 2012

O2 sensors been checked/changed? CATs possibly getting plugged? EGR/throttle body may need cleaning?

Few more possible checks. Keep us updated, hope you can find the answer.

txab · January 30, 2012

Fuel quality?

XRMAN · January 31, 2012

Changed all 4 O2 sensors 2 yrs ago. I don't have EGR, that I can tell. Did have problem with the EVAP system,the the dealer put some update on it. The the mileage really got crappy. Seemed to get better mileage before the update, I was talking to my friend at work and he said his mothers 4.8 did the same thing. I'm leaning toward that causing my problem now. Well anyone have any other Idea PLEASE put them up. Yes gas quality don't help either.

GMstrong · January 31, 2012

Bosch plugs are no good.Start there go back to NGK's thats all i run.Do the wires also.

XRMAN · January 31, 2012

Yeah good point. How about E3 plugs? See good reviews on them. I'll have to ohm my wires cause there not too old. Anyone use Lucas fuel treatment that is green? OK Thanks I'll keep posting if I get any where.

txab · January 31, 2012

Stay away from E3 plugs too. AC Delco or NGK. Use Cheveron Techron concentrate plus for a fuel injector/system cleaner. Buy your fuel from a listed Top Tier fuel dispenser.