Fuel Economy!

XJay · Dec 11, 2006

My fuel economy on my '99 has progressively gotten worse over the last two years, and I've seen a change (for the worse) in the last three weeks. Next weekend, I'm changing the air filter along with Seafoaming the upper end of the engine - would it be helpful to run some through the gas tank/fuel system as well? I'll also be changing the fuel filter, plugs, and wires come February.

My questions are simply, what could be killing my fuel economy, and what else can I do to improve it?

Also, my engine stumbles a bit between 1100 and 1400 RPM, could this play into the problem with the fuel?

One more -will a coldair induction kit improve or worsen fuel economy?

Thanks in advance...

Adverse2Change · Dec 11, 2006

You're taking the proper steps to improve it. A drop in K&N will help a small bit with MPG, as will a CAI. Are you also keeping up with your tire inflation and wear?

02ponypackage · Dec 11, 2006

Check tires, maybe a better intake CAI with K&N or any good filter, fuel filter change, along with ne other needed filter changes

XJay · Jan 25, 2007

I've changed the air filter, fuel filter, and plugs/wires. I've Sea-Foamed the fuel system (via the gas tank) and the cylinders (via the intake vacuum hose). Tires are correct size and inflation.

Still, fuel economy is getting *ridiculously* worse. What else is there to do?????

ChingonStang · Jan 25, 2007

It's probably the gas. This ethanol mix is crap.

232Mustang95 · Jan 25, 2007

ChingonStang said:
It's probably the gas. This ethanol mix is crap.

ChingonStang · Jan 25, 2007

232Mustang95 said:

V6muscle00 · Jan 25, 2007

im with chingon.. the ethanol mix sucks
but more importantly we def need more wookie and maybe some cowbell too

raz54 · Jan 25, 2007

You can never have too much cowbell......

Have you had the cats checked to see if any are plugged?

XJay · Jan 26, 2007

I read in another fuel economy thread where someone suggested making sure that the Overdrive is still on.

What is 'Overdrive', and how does it affect fuel economy? I'm assuming that since the light on the dash comes on when it's off, that Overdrive is meant to usually be on?

I know where the overdrive button on my automatic stick shift is, but when I press it, nothing happens (no light on the dash) - what does this mean, and could it be affecting my fuel economy?

XJay · Jan 29, 2007

Help?

232Mustang95 · Jan 29, 2007

The bulb might be busted and yes that will hurt your milage if it's off.

ChingonStang · Jan 29, 2007

232Mustang95 said:
The bulb might be busted and yes that will hurt your milage if it's off.

Give Me TP · Jan 29, 2007

OD is on by default every time you start the car, so it is unlikely that OD being off is the source of the problem. To comfirm though, find out what the rpm is at a given speed and compare that to what others on here experience with similarly equipped 99 models.

Also +2 on need more kowbell

TheCrazy1 · Feb 8, 2007

The rpm should be around 2200 or so at 70mph. At least somewhere in the low 2000 range. If it's way higher, then overdrive has left the vehicle! Sounds like you've done everything there is to do as far as basics to improve the mileage. What exactly is it getting per gallon? My g/f has a 2001v6 with manual trans and she averages about 23 to 24mpg. On a road trip, it'll do around 30! You say it stumbles a bit too... it might be worth your while to replace the coil pack... they seem to go out and cause misfiring, stumbling, etc.... How many miles are on your car?

XJay · May 26, 2007

I've around 135,000 miles on my car. I'm wondering if I need to replace the fuel injectors......am I getting ethanol at the pump now?

AP1995V6 · May 26, 2007

I usually get around 300 miles before I fill up - in the neighborhood of 1/4 tank.

Is your CEL on? Running rich will definitely cause your gas mileage to crap out. Driving habits affect mileage alot. I dogged my car one tank and got around 18mpg. "Normal" driving got me around 22. And Casual driving got me 24. Most of my driving is on interstate or city driving so I never see anything over 25.

Another thing you could do is to pop out the spark plugs and check their appearance. Make sure they're gapped correctly and such. Check brake pads for wear. A siezed brake caliper will make your gas mileage drop as well. Check the emergency brake to make sure it isn't sticking.

XJay · May 26, 2007

AP1995V6 said:
I usually get around 300 miles before I fill up - in the neighborhood of 1/4 tank.

Is your CEL on? Running rich will definitely cause your gas mileage to crap out.

Forgive me, what is a CEL?

232Mustang95 · May 27, 2007

CEL = Check Engine Light

jefferz · May 27, 2007

XJay said:
Forgive me, what is a CEL?

I think on the 99-04s they will say Service Engine Soon instead of Check Engine...just so you know. I just cant remember off the top of my head cause mines never been on in my 02 GT

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