Does anyone else on here have a gmt800 5.3 with 4.10 gears? So I'm just trying to figure out what is causing poor gas mileage in my 04 or if it's even really anything to worry about since it's still not too bad. Just got done with a 700 mile trip and averaged 14.5 mpgs all highway. What's weird is I get 15 or 16 in the city. I just fixed the egr vent valve and the CEL hasn't come back on. I was hoping this was the issue and would boost gas mileage. Is there anything else I should check? Or is this just normal for a 04 suburban with full time 4wd and 4.10 gears? Thanks.
Bad Gas Mileage?
- Thread starter 04Beast
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FrankU
Full Access Member
That is normal for a vehicle with 4:10 gears and 5800 lbs
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osiris94ej
Full Access Member
For reference my 04 with 3.73 and a heavy wheel Tire setup with a roughly 95lbs per corner. My city average is 13.1 mpg. This is on a 32" a/t's with a 10" wide wheel. About to make a 600 mile round trip mini vaca and I can give you a comparison for highway mpg.
I honestly think that's the normal range. Are they factory 4.10's? If not did you have the computer recalibrated for the steeper gear?. I have been looking to jump from my 3.73's to a 4.11 to reduce the slouchyness this heavy suv has.
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I honestly think that's the normal range. Are they factory 4.10's? If not did you have the computer recalibrated for the steeper gear?. I have been looking to jump from my 3.73's to a 4.11 to reduce the slouchyness this heavy suv has.
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Factory 4.10. After doing more reading it appears I may have a fuel pressure regulator or fuel pump issue. Can this affect mpg? Truck starts hard the first time and usually have to wait a few seconds to prime it so it will start the first time. Run's great after that though.
osiris94ej
Full Access Member
After the first 150 miles or so average is only up to 13.8 so I think it's about normal for numers.
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osiris94ej
Full Access Member
Pretty sure that's normal now. This is 80mph the whole way with wind and heavy traffic.
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Pretty sure that's normal now. This is 80mph the whole way with wind and heavy traffic.
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Thanks for the info!
retiredsparky
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you could try experimenting with different speeds on longer trips. Maybe lower would increase mileage.
osiris94ej
Full Access Member
Sorry didn't realize you asked about the fuel pump issue. If you have to prime to start it or its hard starting. Check the fuel pressure key on engine off, 55-62psi is the specification. If it won't hold that pressure with the key off for at least 15min I'd say the pump is allowing pressure to bleed off and lets the fuel backwards through it.
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I have an 04 XL 5.3 flex fuel,
I have an 04 XL 5.3 ff, gt4 3:73 gear, currently getting 14.9 highway and 15.2 combo, not sure what has changed but until recently I was getting 19 - 22 highway and 15.7 combo/city, still runs great, no codes, no lights, no answers just miss the great highway mpg it had. My 4th one, all have pushed 18-20 on the highway. When i get time I'll check into it an share the results
