Very poor fuel mileage

Hello everyone!!! New to the site, so far I'm very impressed.

In 2000 I bought a 2000 GAGT coupe and loved the car. It got 22-24 mpg in city and 28-30 on freeway. I sold it in 2003 and bought a 2003 GMC 1\2 ton EXT. cab truck to tow my snowmachine and dirt bike.

Since then I got married in 2004, my wife also has a 2000 Chevy 1\2 ton EXT. cab truck for the same reasons as me.

But with gas prices so high it was killing us to have two trucks. So we bought a Black 1999 GAGT sedan with 34,000 miles on it, very nice car. The car runs great, plenty of power, my only complaint is that in town it is getting 17 mpg and on the freeway at 75 mph it gets 23mpg. I know it is winter so it will get a little worse mpg, but I think this is to low. I have replaced the fuel filter, air filter, engine oil, checked the spark plugs (they are fine), had computer scanned (no error codes).

Any ideas please.

I did a search on this forum and found some threads with the same problem. Could you guys please post what fixed your car?

I think the catalytic converter is fine, it does not smell like rotten eggs while running, the engine does not sputter or hesitates.

Could it be an O2 sensor, plugs and wires, or a pcv valve?

Any advice would be greatly appreciated.

Thank you in advance.

[H.O. Driver]

The best bet is the o2 sensor, but the car is almost 7 years old now, so it wouldn't be a bad idea to have the fuel injectors cleaned and flow matched to make sure they are good to go.

This may seem out in left feild, but it can't hurt to check, pull the intake tube after the maf and see if there is a tornado or something like that in there, there have been a few people that have bought used cars (not all GA's) that have those in there and they hurt fuel mileage.

[Panacea]

I average 17-19 mpg in the winter.

[nascarnate326]

Originally Posted by Panacea

I average 17-19 mpg in the winter.

So do I.

[excitement]

I get around 24-25 mpg in the winter. 26 mpg if I play nice. Check the fuel pressure regulator. I had a leaky one that caused my mpg to drop. Also, have them check to see that the car is executing the correct programming for engine management. The default values could have be changed for more power by the previous owner.

[nascarnate326]

My cars got 130k miles on it. Im lookin for a diff car anyways.

[Panacea]

Originally Posted by excitement

I get around 24-25 mpg in the winter. 26 mpg if I play nice. Check the fuel pressure regulator. I had a leaky one that caused my mpg to drop. Also, have them check to see that the car is executing the correct programming for engine management. The default values could have be changed for more power by the previous owner.

Is that all highway, or a mixture of highway/city?

17-19 is all city.

I can get 27-33mpg all highway.

And I get 21-25 mixture.

[excitement]

Originally Posted by Panacea

Is that all highway, or a mixture of highway/city?

17-19 is all city.

I can get 27-33mpg all highway.

And I get 21-25 mixture.

Right now, it's about a 60/40 (highway/city) split so I get the 24-25 mpg result. All highway my best was 29.7 mpg. That was last summer with the AC running. For city, my best 24 mpg. During the summer, I get 26-27 mpg doing the 60/40.

[SikMindz]

Seafoam?

[Panacea]

Originally Posted by SikMindz

Seafoam?

Definitely wouldn't hurt, but if it's cold like it is here, I would say it's normal.

[tomh]

i normally get like 25-26 normally now.. i used to get close to 30.. i put new plugs and wires in my car.. got me 29 for the first tank.. now as of today the second tank is back down to 25... so now im going to try to find a pvc value and repalce it cause they are cheap im told. and look into the price of an o2 to see if that will help me any

Well I changed the 02 sensor in front of the cat, PCV valve, and spark plugs. I will see if this improves my gas mileage. On the last tank I went 185 miles on 12 gallons of gas, which is 15.4 mpg in town driving (I get that good with my truck). If I can't get any better mileage then I am going to sell the car.

How many RPM's are you guys turning at 75 mph? I am turning 2200.

[Panacea]

Change your oil/oil filter, change your air filter, fuel filter, get your injectors cleaned at the dealership, don't let the RPM's get above 22-2500rpms while accelerating. Also, make sure your tires are properly inflated. Also, you may want to make sure your coil packs are okay as well as your spark plug wires.

As for driving at 75mph, that sounds about right.

[DrFabulous]

I get around 21-25 mixed driving, 28 or so highway this winter. But I have the 2.4.

[Chevylover54]

Don't be surprised if it is your catalytic converter. Mine never smelled. Just lost power and gas mileage. First to go was the mileage.

[CrucialTK]

at 75, I turn 2250 rpm (approx)

[sleighbor]

I just bought a 2002 GT with 32,000 and am only getting 20 mpg with mostly highway driving. I thought I was supposed to better than that with this car. Any info on this would be greatly appreciated!

Kevin

[DrFabulous]

Did you, I don't know, READ THIS THREAD first?

[sleighbor]

I read the entire thread first and all the others. It seems there are varying theories out there. People have change filters, batteries, sensors. They get decent mileage for a tank and then back to poor mileage. I was hoping someone may have found the right answer. That's all I meant.
Kevin

[Slim]

Originally Posted by sleighbor

I was hoping someone may have found the right answer. That's all I meant.
Kevin

There is an easy answer. Go easy on the go pedal. GAs get thirsty very quickly. You baby it and the gas mileage is good. Drive it even a bit hard and it gulps fuel like mad.