HORRIBLE gas mileage in my gm 4.8V8

[exalted512]

I have an 04 GMC extended with the 4.8. It has 32k on it and I'm getting absolutely horrible mileage. I average about 9.5mpg. Its all city driving, but I should be getting at least 14 at the lowest. I had a 96 3/4 ton w/ the 5.7, almost 200k and I was getting a regular 11 mpg and i drove it a lot harder than i do this truck.

I thought it might be the fuel filter, but its in the gas tank on the 04+ models and not supposed to need to be changed. Other than the air filter, I dont know what else it could be. Even then, I dont think an air filter would be so constrictive that it would hurt my gas mileage that bad.

Is this something I could take to GM under warranty??

Truck seems to be running great. Great pick up, I can chirp the tires at 30mph. Its been serviced by GM before for the power steering steering. Im not sure if they do a check on everything or not though. Ive hooked up my code reader to it and nothing came up. I changed the oil recently...Im lost...any suggestions?
-Cody

[disneyjoe7]

Sorry to say it's just my $.02.....


IT's the F'ing air quality ****.... Saving the F'ing world..... OK so we get ****ty gas mileage then we bitch about oil / gas usage we can't have it both ways....


I'm a bit pissed about my 99 4runner V6 4.0 engine gas mileage 17.5mpg. It's a timing issue it must be so F'ing retarded for emissions it forcing us to give it more gas for the same power needed to move your car / truck. I could build the 7.4L V8 Pontiac engine and get 20 mpg easy.

[nesticle]

Is this 9.5 around the city? You should be doing waaaay better than that. As you said, at least 13/14 even if you're heavy footed.

Well I can't complain about gas consumption.. I have a lead foot and I still get 30mpg (then again, my car has about 3 litres less displacement).

[RuSsMaN]

Change your Fuel Filter. - Nevermind, re-read your post.

Are you leaving the tailgate down?

[bobman1235]

I'd say you've got a plug not firing or something, but you wouldn't be running so smooth if that was the case.

Sucks man.

[aaharvel]

master cyl.?

[Dennis Gardner]

Warranty may not touch it, they will tell you its your driving habits. I have an employee that just bought a new '06 Civic 4 cyl and Honda is telling her tough **** on 20/27 city/highway. This should be a car that gets close to 40 shouldn't it?

[whitetruk]

i have heard that gas company`s leave ethynal(something like that) out of the gas from nov to march.and that will make for horrible gas milage,i myself have lost milage in both my car/truck.
i dunno tho thats just what i heard,ohwell gotta go fill up

[exalted512]

i dont leave my tailgate down, but i didnt on my old truck either. This is pretty insane, I get an 8 yr newer truck, almost a liter less, with over 150k less miles and i get worse gas mileage.
-Cody

[bobman1235]

I've heard somewhere that leaving your tailgate down actually DECREASES fuel economy in some cars, by some miracle of physics.

I have a tonneau cover so I never really tested the theory, but... figured I'd throw it out there.

[PolkThug]

Go to a dyno shop and get your Air/Fuel ratio measured, sounds like you're running too rich.

[beardog03]

you may have a injector problem..
rum her down to 1/4 tank, put a bottle of chevron techron in it, and fill up with mid or high grade..
take her out on the highway a few times and see if you can get the crap out..

when I first got my truck, they had ran it so low in the fuel tank, that the stuff at the bottom was making an injector stick..and not spray correctly, and the other started to follow suit...

[venomclan]

GM probably wont touch it for gas mileage warranty. Check your tires, make sure they are fully inflated. I would still also check the fuel filter, even though it should not need to be checked, its a GM-I have had too many GM products fail before they are due. Our Tahoe transmission failed at 32k.

Also make sure you are using the right grade os gas the manual calls for.
Venom

[howie777]

I've heard somewhere that leaving your tailgate down actually DECREASES fuel economy in some cars, by some miracle of physics.

I have a tonneau cover so I never really tested the theory, but... figured I'd throw it out there.

Mythbusters did a show on this. They found the same result, gate up for bets MPG. Something to do with a air "bubble" being created in the bed which sends air up and over the bed instead of into it, thus creating less drag than with the gate down. The air "bubble" doesn't form if the gate is down.

Pretty interesting actually, they showed models of this occuring.

Howie

[bobman1235]

Nice! Good ole Mythbusters.

[beardog03]

they came out to work and sank a boat at the end of our pier...

They did it all wrong if ya ask me..

boats don`t sink like that...I know, I have lost a couple in the bay..
One in 60ft of water..three planks poped at night...
when I poped the hatch to have a look, it was waaaay too late...down she went...34ft Stevens...blub,blub ...friggin swoosh.....


sorry for the de-rail... ;)

[disneyjoe7]

Question is the low MPG is new, so when you got this truck it was higher MPG?

[MacLeod]

Mythbusters RULES!!!

Damn Cody, that is pretty horrid mileage. My Beloved Ram (4.7) gets about 13 around town and mine weighs 6000 pounds! My 2000 Ram with the 5.3 also got about 13 and Chevy makes outstanding engines.

Since its still under warranty it may not be a bad idea to run it up to your local Chevy dealer and let them have a look at it.

[danger boy]

you should of got a Ford... (runs and hides) :p

[exalted512]

next time i fill up ill use the good stuff and put a bottle of injector cleaner through it, maybe thats it.
-Cody

[exalted512]

you should of got a Ford... (runs and hides) :p

id rather get bad gas mileage than be humiliated on a daily basis :D
-Cody

[MrNightly]

Can't touch the 2006 F-150. Sharpest truck out there. Every chevy i've owned has rusted thru... pieces of crap. ;) Hehehe

[wodom1]

I only get around 9.5 mpg in the city in my '02 4.7L V8 Durango. The highest I've ever had it was on a trip to LA to visit my folks -- avg. mpg was 17.5 mpg for an 1800 mile trip. Good luck finding the cause/treatment. If you somehow increase your mpg, post how you did it. I'd be interested to see if it could improve my own.

[cam5860]

Tune it up man put some new plugs and wires on it. It don't have to be skipping to be getting bad gas milage. The gap on the plugs are probally burnt up. Also a wire should read between 6 to 12 kilovolts with these computer systems now they can make up for so much.

It's not uncommon for a wire to read high 18 to 21 kilovolts and you not be able to feel it miss or breakdown. When a wire reads high it's doesn't mean it's not sending fire to the plug. It's just the fire from the coil will be a lot weaker by the time it gets to the sparkplug.

Therefore the plug has a weaker fire in the combustion camber allowing a lot of gas not to be burned and sent out the exhaust.

[disneyjoe7]

Cam, by Kilovolts do you mean KiloOhms?

[cam5860]

No fire coming from a coil is measured in kilovolts.

[Tour2ma]

(Mythbusters) came out to work and sank a boat at the end of our pier...

That was the "refloat a boat with ping-pong balls myth"... CONFIRMED

I'm not sure the tailgate test wasn't flawed, but ut was entertaining as ususal. Fun show...

[hoosier21]

I have had Chevy 350 454 5.7 5.3 and one 4.6, the 4.6 was the worst friggin engine I ever drove, no pep, and as bad if not worst gas milage than the 350. I got the smaller engine for better gas milaage and it backfired on me, actually lost gas milage.

Good luck , trade it in for a 5.3 and you will be thankful you did.

[disneyjoe7]

No fire coming from a coil is measured in kilovolts.

Ok my bad....

[dkg999]

Get a 5.3L! I believe this is the old 327 Chevy motor. I have a 2004 Chevy 1500 extended, 3.73 rear end, and I get right at 20mpg running 75 mph on the interstate, and around 15 mpg pulling a 2500 lb enclosed trailer.