03 Tahoe Z71 runs great, bad gas mileage.

[Brad Nelson]

I just picked up an 03 Tahoe Z71 With 180k on the clock. Runs very smoothly, and there are no check engine lights. It is the 5.3. I seem to be getting pretty crap fuel mileage, 12-13 around town and 14-15 highway. I have a fresh air filter, fresh oil change, I have ran Lucas injector cleaner, removed the Maf and hoses down with Maf cleaner. She sits on stock size tires at recommended pressure. Temp runs like it has a 185 t-stat in it, but I don’t think that should make THAT big of a difference. What gives? I was hoping you gurus would have an answer.

 

[HiHoeSilver]

I just picked up an 03 Tahoe Z71 With 180k on the clock. Runs very smoothly, and there are no check engine lights. It is the 5.3. I seem to be getting pretty crap fuel mileage, 12-13 around town and 14-15 highway. I have a fresh air filter, fresh oil change, I have ran Lucas injector cleaner, removed the Maf and hoses down with Maf cleaner. She sits on stock size tires at recommended pressure. Temp runs like it has a 185 t-stat in it, but I don’t think that should make THAT big of a difference. What gives? I was hoping you gurus would have an answer.

View attachment 217552

What kind of fuel are you using? And how do you drive it? Honestly, your numbers are pretty average.

 

[Brad Nelson]

What kind of fuel are you using? And how do you drive it? Honestly, your numbers are pretty average.

It’s rated 15 city and 19 highway.
I drive like a grandma. I normally get a cpl of mpgs better than advertised on previous vehicles I have owned due to my sensible driving. I have tried fuel from a few different stations to see if there would be a change. I always fill up with 87 e-10 everywhere around here.

 

[HiHoeSilver]

It’s rated 15 city and 19 highway.
I drive like a grandma. I normally get a cpl of mpgs better than advertised on previous vehicles I have owned due to my sensible driving. I have tried fuel from a few different stations to see if there would be a change. I always fill up with 87 e-10 everywhere around here.

You will likely see an extra mpg or 2 running at least 89. I promise there is not an 00-06 on this forum regularly getting much above 16-7, let alone 19.

 

[Brad Nelson]

I will give the 89 a try. I would be happy to get the rated 15 city. The 12 mpg I have been getting sucks.

 

[HiHoeSilver]

I will give the 89 a try. I would be happy to get the rated 15 city. The 12 mpg I have been getting sucks.

Do you have a traction control button? If so try turning it off.

Also, do you have a scan tool to look at your live data? You might look into your fuel trims and O2 sensor data.

History on plugs/wires? Any way you've got a brake caliper dragging or a beating going bad?

 

[Brad Nelson]

Do you have a traction control button? If so try turning it off.

Also, do you have a scan tool to look at your live data? You might look into your fuel trims and O2 sensor data.

History on plugs/wires? Any way you've got a brake caliper dragging or a beating going bad?

No traction control on this one.

I haven’t changed plugs/wires yet. No sign of a misfire though. The motor runs smoother than my 2014 HEMI. They are next on my maintenance list.

The truck runs incredibly straight and smooth. Wheel bearings are perfect. No sign of a sticky caliper. I will jack it up and check to be sure when I get a chance.

I only have a basic code reader. I could take it to a shop, but I am trying to avoid the cost.

I wonder if the o2s are bad enough to run super rich, but not bad enough to trigger a code?

 

[HiHoeSilver]

No traction control on this one.

I haven’t changed plugs/wires yet. No sign of a misfire though. The motor runs smoother than my 2014 HEMI. They are next on my maintenance list.

The truck runs incredibly straight and smooth. Wheel bearings are perfect. No sign of a sticky caliper. I will jack it up and check to be sure when I get a chance.

I only have a basic code reader. I could take it to a shop, but I am trying to avoid the cost.

I wonder if the o2s are bad enough to run super rich, but not bad enough to trigger a code?

A code will not usually appear until one of the long terms hits the +25 limit, at which point it will trigger a 0171 or 0174 lean code.

 

[cam3439]

What gears do you have in the differential(s)? 3.73 is a good midpoint, but if you have the 4.10’s then that’ll explain your mpg.

 

[Brad Nelson]

I am not sure, I will have to check the codes. They really came with 4.10 as an option? That is nuts.

 

[pt1965]

i previously drove an 02 yukon xl 2wd for 10 yrs from btwn 65k and 202k miles and on long trips i still only got 14-16mpg overall. maybe it got better than that 1 direction but probably lower coming back. mine had a 3.73 rear. i currently have a 2010 burban 4wd with 6speed, cylinder cancelling,3.08 rear and still only 16mpg overall, got 18mpg on 1 trip.
i figure its a full size truck that does everything, what do i expect. if it got the published 21mpg all the time everybody would own one!

 

[Brad Nelson]

i previously drove an 02 yukon xl 2wd for 10 yrs from btwn 65k and 202k miles and on long trips i still only got 14-16mpg overall. maybe it got better than that 1 direction but probably lower coming back. mine had a 3.73 rear. i currently have a 2010 burban 4wd with 6speed, cylinder cancelling,3.08 rear and still only 16mpg overall, got 18mpg on 1 trip.
i figure its a full size truck that does everything, what do i expect. if it got the published 21mpg all the time everybody would own one!

No doubt, even if I am stuck getting 12mpg I am still happy with it. It still does everything it should. I just figure if a $100 fix saves me a few hundred in fuel over the next few years I might as well do it.

 

[latvius]

I get about 13 and change, works for me. All those foreign SUV's that I have ridden in that get a little better MPG all ride like tin cans and as roomy as a third class seat.

 

[08HoeCD]

This thread reminds me of a funny story:

A few years ago, one of my coworkers showed up Monday morning at the office with a '99 Toyota Land Cruiser. He had always loved their look and he found one in great shape at a great price. He was talking about it all day and seemed like a proud father boasting about his newborn baby.

Two days later, he is very depressed and says he needs to sell the Land Cruiser. I was surprised by this odd development, so I asked him why. He says that he never thought about fuel economy before buying the vehicle, since he had always driven smaller cars and it was never an issue. He was shocked to be getting only about 11 mpg on his long commute to & from work. He said he couldn't afford to operate the vehicle.

So he went from being the proudest, happiest vehicle owner on the planet to being totally bummed out. All in the space of about 48 hours. LOL

 

[Brad Nelson]

I would never ditch a ride I loved due to poor mileage. That’s just the price you pay to play imo.

I checked my codes in the glovebox. Mine is GT4 so that should be 3.73s That explains some. I still feel I could be doing better, but the reality is the issue is probably just a bunch of things getting old. Not likely that I will find any one major issue. I would like to hook it to a scanner to see what the O2 trims are. But that’s probably the extent of it.

 

[yukonxlv]

i previously drove an 02 yukon xl 2wd for 10 yrs from btwn 65k and 202k miles and on long trips i still only got 14-16mpg overall. maybe it got better than that 1 direction but probably lower coming back. mine had a 3.73 rear. i currently have a 2010 burban 4wd with 6speed, cylinder cancelling,3.08 rear and still only 16mpg overall, got 18mpg on 1 trip.
i figure its a full size truck that does everything, what do i expect. if it got the published 21mpg all the time everybody would own one!

Daughter was concerned with increase in fuel consumption on an 02 Yukon with 235000 miles. Found plugged pcv system. Pulled driver side valve cover off to clean carbon from the built in vent. Gm is on version 3 of redesigned valve cover to fix this problem. The jury is still out on fuel consumption but it sure helped on fixing the oil leaks of the 5.3.

 

[yukonxlv]

Plugged pcv system?

 

[SnowDrifter]

You will likely see an extra mpg or 2 running at least 89. I promise there is not an 00-06 on this forum regularly getting much above 16-7, let alone 19.

Hi

I'll generally average in the 19 to 22 range on a highway trip of I keep it below 70

Drops off pretty quick above that to the 16 to 17 range but I also drive around 80.

Around town average puts me at 15.7, at least according to the DIC

3.42 gears


I would agree that 14 highway is a bit on the low side unless it's 20 degrees and you're driving into a head wind the whole way

 

[grouch]

I just picked up an 03 Tahoe Z71 With 180k on the clock. Runs very smoothly, and there are no check engine lights. It is the 5.3. I seem to be getting pretty crap fuel mileage, 12-13 around town and 14-15 highway. I have a fresh air filter, fresh oil change, I have ran Lucas injector cleaner, removed the Maf and hoses down with Maf cleaner. She sits on stock size tires at recommended pressure. Temp runs like it has a 185 t-stat in it, but I don’t think that should make THAT big of a difference. What gives? I was hoping you gurus would have an answer.

View attachment 217552

I wish I got that good a fuel economy reading. I get 9 around town and 11 on the highway, with a tail wind. However, I have some really NASTY off road tires that eat snow and mud. Now, a cooler thermostat is BAD mojo on a fuel injected engine. You MUST run the OE temperature thermostat. FI uses "open loop" mode to compensate for the lack of a choke. Your computer is pumping extra fuel into the engine to try and warm it up. I have seen substantial changes by going back to the proper heat range. Your heater will work better too.

 

[swathdiver]

Brad, it's winter in most places. Winter brings along poorer road conditions that deliver less mileage. Winter blend fuels also hurt mpgs a little. Then you didn't say what kind of tires you're running. 3.73 gears are not likely to help your highway numbers either.

Run top tier fuels.