25% decrease in MPG

[KenC]

I've noticed that my gas mileage has decreased from ~30 combined to 22-24 mpg combined.

I've changed within the past 10k miles:
- plugs, wires
- cap, rotor
- fuel filter
- thermostat and coolant
- O2 sensor

I'm wondering if it's just the cold weather 30-45 most days and the increased ethanol content in the gas during the winter months...

[browntown]

i think portland i.e. (Multnomah, Clackamas, Washington and Yamhill counties) are the only places in oregon that have the winter fuel rule. I was under the impression that they repealed it too. I don't believe the valley uses it but I could be wrong. For your changes I would think you would get better mileage, but its always possible your car wasn't running at full force before the changes, and now that your car is burning the gas more completely you're using all the gas and hopefully getting a little better throttle performance out of it. Dunno, snow tires will definitely drop your mileage.

[KenC]

I'm pretty sure we still have the 10% Ethanol here during the winter. I recall seeing one of the stickers on the pump.

[EtaSport]

Pretty much all fuel has ethanol in it today. Increased alcohol content in the fuel will make your car run lean. Which should help with the excessive usage. My car comes from 28 in the summer to 26 in the winter, but your drop is a little high.

You may want to check fuel pressure and afm output.

[KenC]

You may want to check fuel pressure and afm output.

How?

[Charlie]

Even though it's new(er), I'd check the O2 sensor. That big a change in mileage usually sounds to me like the car is running wide open rich. Are you running an OEM BMW O2 sensor or a modified one?

-Charlie

[EtaSport]

Best way to check the regulator is to hook up an inline pressure gauge. Then unhook the vacuum line to the regulator, you should see a slight increase in pressure, if there is no increase the regulator is sticking open and giving you full pressure even at idle which will cause a rich condition.

I agree with the o2 suggestion. It would suck to go out again, but it sounds like an open loop issue. Oh yea, check your coolant sensors too as they affect open/closed loop conditions.

[Hick]

Easy! Speed holes!

[KenC]

The O2 sensor was brand new OEM Bosch (not a modified one). I replaced the coolant temp sensor not too long ago... the temp seems to be fine, too.

Where to I get an inline pressure gauge to check the FPR? Does any one have a picture of one?

Thanks for all of the help.

[Jordan]

Quit your bitching Ken. Suck it up.

-Jordan, 18-22mpg.

[redcarbon]

I found the gas mileage in my jetta went to crap when during the winter when it got really cold in rural new york and I made a lot of short drives around campus. The computer dumps a lot of fuel in for cold starts and my mileage suffered. Not much you can do about that. Maybe that's all it is.

[EtaSport]

Go to an autozone or something to find a pressure gauge. When I need to do check mine real quick, I hook up an oil pressure gauge to it. Any type of pressure gauge rated to at least 50 psi will work.

[KenC]

How do I test the AFM?

[SpecM]

-With an ohmsmeter. Unplug the AFM and raed the ohms accross the termanals.
-Which termanals? How much? Ill leave that to someone else.

[EtaSport]

I dont have my bentley in here right now, but you've got to test the resistance as you move the flap over the pot (potentiometer) and look for a change. You can do it at the unit by unplugging it, and if it checks out, you need to recheck it at the ecu plug. You will have to find which pins are input for the afm. I dont have an L jet diagram.