Truck is Getting Horrible MPG

[Hunter.]

2004 5.3 Z71 is getting horrible MPG, no SES light, new acdelco plugs like 150 miles ago, 40 psi on stock size tires, I'm getting 10 city, 13 hwy, hand calculated driving with 2k shifts. Truck had a bullydog on it before I believe, could it be set on a 93 or 89 octane tune or something? Cats clogged?

 

[Bootstrap]

Mine was stock heigjt getting the same mpg... Cranked in mud tires. I just accepted it

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[Jared]

10 seems rather low

 

[Hunter.]

Mine was stock heigjt getting the same mpg... Cranked in mud tires. I just accepted it

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Stock NNBS sierra 17" wheels and Goodyear AT/S take offs, not agressive at all.

10 seems rather low

My dad had an identicle truck to this one and got 16 MPG consitently for the 5 years he owned it. Truck has 3.73 gears btw turns ~2100 rpms at 70 mph.

 

[Bootstrap]

Nnbs? Thought it was an 04.

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[Hunter.]

Has NNBS wheels.

 

[Dakota]

Nnbs? Thought it was an 04.

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Just nnbs 17s

 

[Bootstrap]

Oh. Idk never figured mominene out. You seafoam? I never did, but also heard its dangerous.

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[Jared]

dangerous, where did you hear that? I've done two cars.

 

[Bootstrap]

Maybe its engine flushes.. I know those are bad.


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[Jared]

I've heard mixed opinions, most saying not to flush them. I did have my plugs foul out doing seafoam.

 

[Bootstrap]

I've heard mixed opinions, most saying not to flush them. I did have my plugs foul out doing seafoam.

Damn, i have bramd new plugs in mine too

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[2005_Silverado]

I kept my old plugs in case i wanted to sf its not 100% that ur plugs will foul but its better to change them after

 

[Cuban.]

shit. I'm getting 6 mpg city with my obs leveled on 33's new plugs and wires > 50 miles ago. idk wtf I did to deserve the POS but id love to get rid of it lol it used to get about 10-12

 

[Jared]

One reason why it made me selling mine that much easier. I was getting 13 stock, wanted to lift, but held out. Then it went to shit with the misfire, sat for about 2 years, then I said fuck it, sold to a guy in Houston who built a trail rig out of it.

 

[slicksierra]

Stock NNBS sierra 17" wheels and Goodyear AT/S take offs, not agressive at all.


My dad had an identicle truck to this one and got 16 MPG consitently for the 5 years he owned it. Truck has 3.73 gears btw turns ~2100 rpms at 70 mph.

16 is what I get with my truck, good to me imo but gf's dads 05 silverado w/ 5.3 and 3.42's gets 17-18

 

[Dakota]

I average 17-18 on the highway, not sure about in town though never bothered to look

 

[Bootstrap]

Still, seems normal to me. Maybe a tune would help you., data log?

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[Ginger]

tune would help.


I personally HATE seafoam, caused more problems then help on a few of my trucks.

make sure your tires are properly inflated. any CEL at all?

you should be getting around 13-16 atleast, i get around 14-18 on mine

 

[ScottyBoy]

I consistently get about 11-12 in town and 15-17 on the hwy. But I drive a heavy ass Suburban too. I have 3.73's and I also have NNBS Sierra 17's with AT tires. Stock height, but front torsion bars are cranked about 3/4-1inch.
I remember back when gas stations sold pure gasoline with NO Ethanol, I used to average 14-15 in the city and 18-19 on the highway.