Bad Gas Mileage?

Paint King · July 30, 2008

I'm sure this topic has been beat to death. But, I have a 2000 chevy silverado with the 5.3 reg cab stepside short bed 4x4. I also do have 285's all around. I have fresh oil, new plugs and wires, and a fuel filter.

I'm pulling 10 town and 14 highway. My dads 2001 2 wheel drive gmc sierra 5.3 ext cab is getting around 16 town and a hair over 20 on highway.

Any idea why my mileage is so much lower. I under the bigger tires and the 4 wheel drives part but the rest of the truck would be lighter with the rreg cab and lightest bed they make.

I have also scanned the computer and nothing comes up.

Thanks,

Kyle

99silverado1500 · July 30, 2008

that seems close to average. I have a extended cab short bed 4x4 and i average 11-12 city, normally, on city stretches i can pull 13. Highway is anywhere from 14-15.

Paint King · July 31, 2008

Hm. I just assumed it'd be higher than that.

Paint King · July 31, 2008

I've also noticed over the last week my truck has been acting weird on start up which is why I changed plugs and wires but it wasn't the cause.

It starts slower sometimes two or three tries. But, if I let fuel pump prime it starts first try but doesn't always want to idle will idle down to 200 then up to 700 repeat and makes it to a steady 500. After takeoff never gives me a lick of truble. Just don't know why on startup it's been acting weird since I have no codes.

Kyle

99silverado1500 · July 31, 2008

Mine only does that if I start it up and give it a quick shot of pedal, it will go down to 200, go up to 700+ and when I let off go b ack to 500. My startup "issue" is if I dont hold the key in the Run position long enough it sounds like 2 pistons dont have fuel or like they shudder or knock real quick, thats the best way I can describe it. Ive heard it on many suburbans, silverados, and sierras, I dont like hte noise, but its normal I guess.

2000DV4.8 · July 31, 2008

Bad cats can cause a drop in fuel economy. Does the exhaust smell like rotten eggs?

99silverado1500 · July 31, 2008

My exhaust has a wierd smell. Its no way rotten eggs. Its like a almost hot smell, like its like running lean almost. Theres a slight fuel odor on start up, but it has 105000 miles so thast sorta normal, but Id describe it more being hot smelling, my pipes have NO carbon inside them which is wierd.

July 31, 2008

wow your gas mileage is bad!!!

i get 14.5 city and i have gotten 19 with a 4 wheeler in the back on only a 50 mile trip lol.... a little further and it would have gone up....

D&SYukonDenali · July 31, 2008

Change your pre-cat O2 sensors. These have a wide tolerance before they trigger a code, but will affect mileage long before that. They usually start to go around 75,000 - 100,000 miles.

Paint King · July 31, 2008

That was going to be the next thing I changed. Truck has a little under 110k miles. But, right now I'm more concerned with the stumble and slow start at idle than the bad mpgs. It seems to be getting worse. I've had the truck for two months and started like a champ for all but the last week.

Is there just two pre-cat 02's?

Kyle

Draenor · July 31, 2008

Have you reprogrammed the speedometer to compensate for the larger tires? That will throw the DIC or your calculations.

D&SYukonDenali · July 31, 2008

Yes, there should be two pre-cat O2 sensors. These sensor could (I'll stress could) be causing your problems.

Paint King · August 2, 2008

Speedometer has not been corrected but didn't think that it would throw off the reading too bad or myabe I'm mistaken? I think I've figured it reads 4 miles slower than I am actually going which means I'm going a little farther than it says. But, I didn't think spending the $300 plus on a handheld tuner would be worth it.

mudmaker · August 2, 2008

i have an 02 burb with the same start up problems. Seems like the fuel pump is getting weak. I thought maybe it had to do with using E-85 but now I think its something different. Maybe the pickup filter in the tank is getting clogged. I haven't run any injector cleaner through it for quite some time either. Ours has 125000 on it and has been starting a little hard for about 5000 miles.