Bad Gas Mileage [Archive] - Forum


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08-23-2005, 08:46 PM
Within the last two weeks, my gas mileage has dropped to just barely over 15 mpg.

I haven't noticed any performance drops or anything unusual like odd smells. Sometimes after driving it, it smells hot, but that's about it. I don't know what the cause of that is. I recently moved to Arizona, so it's hot here all the time.

I always have the air conditioning on, but I wouldn't image that would cause the drop. When I drove over a 1000 miles when I moved here, I was averaging around 25 or so on the highway with the AC on.

I suppose some of the drop would be due to more city driving, but that wouldn't explain all of it.

Any suggestions? (Btw, the car has about 94k miles.)

08-23-2005, 08:54 PM
i bet the ac has a lot to do with it, i rarely use it cuz ive noticed how much gas it really wastes

on another note, have u kept up with the usual maintenance...
fuel filter
pcv valve
fuel injection cleaning

08-23-2005, 09:48 PM
But wouldn't that mean the 10 mpg difference is entirely attribuatble to "city" driving? That seems like quite a stretch given the long, straight, fairly unclogged streets around here.

As for the maintenance, I haven't done anything with any of that. I've only had the car for 1500 miles or so. I've changed the oil, had the transmission flushed (that's a problem for another thread), and changed the tie rod ends. Other than that, it's just like when I drove it off the dealer's lot.

What can I do to figure out what the most likely causes of the gas mileage drop are? I'm a law student living off quite limited school loans, so I unfortunately don't have the funds to guess wrong about the cause too many times.

08-24-2005, 12:47 AM
Your Oxygen sensor may be giving false readings... You may want to look into replacing it.

08-24-2005, 08:31 AM
Just under two weeks ago, I had it in the shop for a transmission problem (of course the problem is pretty recent, so that could be irrelevant). They did the normal diagnonstic computer stuff and didn't notice any problems. Is the O2 sensor something that would show up on that?


08-24-2005, 10:29 AM
Also, does anyone know how much getting the O2 sensor (sensors?) would cost?

08-25-2005, 05:48 AM
I am having the same problem. I wasted 1/2 a tank of gas on 90 miles or highway driving. :( I dont know why but I did.

I did the test the manual mentioned to test the pressure on the fuel line. Well one of two things is messed up..

1) a clogged up return line
2) a bad fuel pressure regulator. My guess is the regulator so I am changing that this weekend. The car is pretty new for it to be a clog (but there can be).
I also posted a thead and has some good replies. Just search down this section or on the next page.

08-25-2005, 09:41 AM
Are there any good ways to test for that stuff if you don't have specialized tools?

08-25-2005, 10:17 AM
It is not a speacial tool. You can pick one up at autozone but they cost like 50 bucks. I am actually selling the part.

It is a gauge that that connects to the port on the fuel rail. There are 2 hoses (1- connects to the fuel rail connection and the other is used to release the gas from the lines).

Let me find the thread that has it for sale. You can see what I am talking about. I also have the Hanes book. It tells you some good info.


test the pressure..

if below the psi (should be 41-47psi).. then check this

if at the correct psi... check this

if above the psi.. check this.

so mine was above the psi range (at 60psi) and only two things. hoping it is the fuel pressure regulator and not a cloged line.

08-25-2005, 10:19 AM

no picture but tells you how to get to it. I can take a pic of it if you want.

09-01-2005, 09:38 AM

A little less than a week ago my battery and alternator died. I got them replaced and my gas mileage went back to normal.

09-02-2005, 07:08 PM

A little less than a week ago my battery and alternator died. I got them replaced and my gas mileage went back to normal.

Well, that solved problem lasted a couple days. Now my gas mileage is crap again.

I'm starting to think my purchase of a Grand Am GT was the worst purchase I've ever made in my life.

09-03-2005, 04:34 AM
When you changed the tid rod ends was there a wheel alignment done afterward?

09-03-2005, 05:48 AM
well if you are a bit hard on accelerating you will average around 18mpg, running that AC will kick you down a bit. I would recommend going on a full tank without running your AC once and recording your mpg.

Ive also found that the fuel gauge in our cars has a tendency to be off from time to time, so you might not be going through as much gas as you think you are. But I wouldnt recommend driving till you are completely empty. Empty gas tanks plus hot weather=destroyed fuel pump.

09-03-2005, 08:09 AM
Well, that solved problem lasted a couple days. Now my gas mileage is crap again.

I'm starting to think my purchase of a Grand Am GT was the worst purchase I've ever made in my life.

That is interesting. When you disconnect the battery and reconnect it, it will reset the PCM/BCM and driveability will change until the car "re-learns" the "best" engine management routine for your car.

Seems there is some reason, related to engine management, that your car is using so much gasoline. If you haven't already, you may want to check into the things people have mentioned--injector cleaning, fuel filter, fuel pressure, etc. in order to diagnose that problem. If you purchased the vehicle used, do you know if the fuel filter has ever been changed? At the mileage you have it is possible the filter has not been changed and it could use a changing at that mileage.

Also I would say that the A/C (in the V6 cars at least), in city driving, does adversely affect fuel economy in a considerable way. It may not be the most comfortable thing to do but try driving without the A/C and see how much your economy improves. The compressor is a variable stroke design, which is good, but if it is hot enough it will run full-stroke all the time anyway and will not be good from a fuel economy standpoint.

09-09-2005, 07:30 PM
I get 23 with my ac on. But at 3.39 a gallon every little bit helps

09-09-2005, 11:13 PM
Lets put it this way, driving all highway I can get 33mpg. Driving all city I can range from 17-21mpg. It is possible. A/C will ruin your milage by at least 30%. Changing your oil, fuel filter, air filter, spark plugs/wires (If need be, otherwise clean and re-gap spark plugs), and properly inflate your tires, and don't use your A/C and you should get better mileage.