more fuel economy issues...UPDATE! PROBLEM SOLVED!

[FirebirdHatesRice]

Alright, here's the deal. About 2 months ago I started getting annoyed by my terrible fuel economy, so I changed my PCV valve and fuel filter. After those were done, there's still no change.

In general I'm getting 150-200 miles per tank with about 80% city 20% highway. Even when I drive "perfect" (easy on gas, easy on brakes, etc.) I get 200 miles per tank max. Aren't the 3.8's supposed to be getting between 20-30mpg? I worked my ecomomy out, and it's between 13-15mpg. Is there anything else you guys can think of thats accounting for the bad fuel economy?

[ December 19, 2003: Message edited by: FirebirdHatesRice ]

[ January 11, 2004: Message edited by: FirebirdHatesRice ]</p>

[Camaro_SLP]

Spark plugs and wires.

[FirebirdHatesRice]

Would Seafoam make a difference?

[V6Bob]

Something in the fuel injection system???

Oxygen sensor????

[hawgs]

Check your tire pressure... sounds crazy but it does effect gas mileage.

[OneQuickV6]

Agreed, tire pressure can cause as much as 10% difference in your mileage. SeaFoam or GM Top Engine Cleaner (same stuff really, different packaging) can help. If you leave some top engine cleaner in every cylinder overnight, and the next morning get it out, you'll see a bunch of carbon junk come out with it. Don't just spray it in, you can actually put it in through the sprak plug hole (don't try to start the car) and let it sit. The next morning with no plugs in, turn the motor over to kind of pump the cleaner out of the cylinders. This is a little more effective than using it in a vacuum line.

[Sean37]

Hey man I'm having gas mileage issues too, even if I drive conservatively I'm barely able to crack 200 miles to a tank. Already done spark plugs, wires, fuel filter, changed out the pcv valve, cleaned the air filter, inflated the tires properly, and it still sucks. I've never gotten an SES light before either. What else could it be?

[snatch]

Yeah Im having the same exact problems, barely any more than 200 mile per tank. I have replaced the plug wires(made a difference), fuel filter, pcv, cleaned the air filter and inflated my tires to 32 PSI. Im not gonna put new plugs in cause Ill be changing them to a colder spark once I get the turbo kit.
Are you guys experiencing any problems with your A4's?
Shane

[memphis_raines]

Sean, part of your problem is the 160* thermostat. I had one in mine for about 3 weeks, then decided to go with the 180* because my car was sucking down too much gas. Mine usually gets about 320 to 350 miles to a tank. You might want to change out your stat. It should help at least a little.

[snatch]

I have a 180* thermo and mileage still blows. Someone mentioned O2 sensors, is their a way to tell when they are going bad, any signs?
Shane

[ December 20, 2003: Message edited by: snatch ]</p>

[awesomeame]

my car, 2002 camaro l36, rarely gets more than 200 miles per tank...230 if i'm lucky. i bought it new, and it has always been like this. i don't understand how ppl are getting 30mpg outta their fbody

--matt

[memphis_raines]

Like I said before, I get between 320 and 350, and it used to be better than that when the car was stock. The most I ever got out of a tank was 417. But there's definitely something wrong if your mileage isn't any better than that.

[magic1872]

Cold weather could have an issue as well

[staticpike]

My recommendation for this:

Start by doing a complete tune-up, get crazy. Wires, plugs, pcv, fuel filter, air filter, thermostat, change the oil, change tranny fluid, change differential fluid, clean the radiator, tire pressures, and the list keeps going... do all the easy "cheap stuff" that you can. Might even consider a pcm reset.

Next, go to the parts store and invest in some fuel injecotr cleaner, sea foam and some restore.

Take it for a test drive when you can. My recommendation would be to pick a day when you have a couple of hours, drive until you need to refill, fill it with the expensive stuff, and then drive back. 2 tanks should give you a good estimate of your mileage and see if you are improving/or staying the same.

If you found you haven't improved, then I would start looking at those O2's. Before I replaced them (~$50 a pop at the auto parts store) I'd get ahold of a scan tool and run some a/f ratio's. how does she sit at idle? While cruising? Full throttle? As a last resort, I'd recommend changing one or both to see if your numbers have improved.

If that doesn't do it, then I'm stumped. The lower thermo's (160 or so) will show a decrease in mpg, but it shouldn't be that low...

[snatch]

Well, I forgot to mention that I changed the oil, reset the PCM as well as ran 2 cans of seafoam through it(vacuum line, oil and gas tank). Hopefully Ill be adding my new tranny so I can change the fluid(redline baby). I am also waiting on my new rearend cover from summit(P/N SME-8510400)to add redline gear oil as well.
The only things I have not done are flush the radiator and change the plugs(going colder range once I get the turbo). With less than 40K miles on her I dont think I need to do the restore.
Can an exhaust leak attribute to poor gas mileage? That and a slipping tranny are the only things that I can think of. I have a new catco cat on their so I dont think its bad yet.
Shane