Have done everything, but fuel economy has DECREASED

Asked by SharpGuy Nov 02, 2011 at 02:49 PM about the 2003 GMC Envoy XL SLE 4WD

Question type: Maintenance & Repair

Purchased this vehicle 2 years ago.  In 2010, I was
getting great fuel economy, I had no complaints.  
500-600lms (300-360 miles) on a tank.  I changed
the air filter in August, and was not getting 600-
700 kms on a tank. (360-420 miles) on highway
use.  A personal best of 740kms on a tank actually.

Roll into 2011.  My mileage was poorer, (I assumed
it was the "Winter Gas, and the additives) then I
added 4 new tires in April, and always keep to
correct pressure.   Tires are Firestone
Destinations...

My mileage was barely 500kms now, on perfect
highway conditions.  I brought it in for a full tune
up...  One of the  O2 sensor was bad.  Had this
replaced. Replaced all plugs with OEM Champion
plugs.  Replaced the fuel filter, and air filter again.  
Also had a universal joint, and rear axle seal
replaced, as it was beginning to leak.  

IT's the 4.2L SLE 4x4 model.   I started a
spreadsheet to keep track of my fuel economy.    I
burn 15L-16L per 100km on highway (at speed
limit) . This is averaging 14-155MPG on highway.  

CITY MPG  - it is now getting 9.5MPG in the city.  It
burns 24L per 100KMS.   This means I can barely
go 300kms in town for $95.00 (30 cents a KM)

Compared to what I got last August/September,
(21MPG or 10.7L per 100km) this is just horrible..

Frustrated, don't know what to do next.  Love my
truck, need to remedy - any helpful advice?  So
much appreciated....

5 Answers

285

I did a custom tune of my PCM (Wait4Me Custom Tunes out of IN) on my 03 Chevy Trailblazer LT. I can pull 25 MPG on longer trips if I am steady on the pedal. I'd replace your plugs with AC-Delco's. What oil are you running? Amsoil is my 1st choice, then Mobil1. Tire pressure is VERY important and so is the AIrfilter (AC-Delco), which are 2 areas you've already covered. I also removed my roof racks to cut down on resistance. The grade/type of gas you use has an effect. Do you run a fuel system cleaner with your oil changes? I run Seafoam or Chevron for my fuel system. Hope this helps.

2 people found this helpful.
60

My gmc envoy burns gas and why do I need to clean the intake or something to get better gas mileage

6 people found this helpful.
30

Hey MKZ, my dog eats food. Why do I need an enema if I can't poop?

3 people found this helpful.
10

All said and done, what about the human factor? There's need for human tune up as well. What about applying a little of truck driving fuel saving techniques? Drive at constant speed, stop over speeding, allowing car to roll on, reduce braking often and sudden, looking ahead, distancing oneself from front runner, etc. There are also fuel saving apps out there.

1 people found this helpful.

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