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.

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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.