Bad Gas Mileage

[Arrowhead]

I've used K&N filters for a long time for both performance and economy.
Hard to beat $36.32 (shipped) for a reuseable filter.


http://www.amazon.com/33-2141-1-High-Pe ... automotive


This product fits your 2004 Pontiac Bonneville
Engine: 3.8L V6 Gas OHV Distributorless Naturally Aspirated SFI Electronic FI MFI
Trim: SE


Or.......$37.69
http://www.amazon.com/33-2063-1-High-Pe ... automotive

This product fits your 2005 Pontiac Bonneville
Engine: 4.6L V8 Gas DOHC Distributorless Naturally Aspirated TPI-SFI Electronic FI MFI
Trim: GXP

[00Beast]

The second one is what you need. It's a different filter between the two, with the GXP's being narrower and smaller overall...

[stevenmamos]

I got 19.2 mpg on my last fill up. Thats 50% highway and 50% city. Is this typical fuel economy?

[Arrowhead]

My 2000 SLE is usually at approx. 22 MPG in mixed driving.

[shipmanlights]

Clean your MAF sensor with MAF spray cleaner. This fixed my gas mileage issue. There are 2 elements. they should be silver. If they look dark,black, or brown. Get the cleaner and spray them. When these are dirty the computer will get wrong readings from the sensor and gas mileage will be effected.

[DRC]

As shipmanlights suggests above, cleaning a dirty MAF sensor can definitely improve fuel mileage. One other often overlooked thing that I found made a difference on more than one occasion is cleaning the IAC valve. A very simple job...2 small torx bolts hold it onto the TB (T20 I believe), once its out clean the tip with throttle body cleaner until all the carbon is removed.

When I bought my Bonneville 2 months ago - after getting what I believed to be poor mileage on my first tank of gas - I cleaned the MAF and IAC, and the next tank I noticed almost 4 mpg difference. So it's worth a shot.

[00Beast]

Another often overlooked sensor is the Oxygen Sensor (O2 sensor) in the exhaust. An old one will be slow or incorrect. When replacing, be sure to either get an AC Delco, Delphi or Denso part. The rest are inconsistent in quality, and NEVER get Bosch for the 3800.

[DRC]

I would suggest taking it into a local shop for a OBD reading...they are typically free of charge. You can get readings on most or all sensors, including both O2 to give you an idea if they are functioning properly or need replacement. Keep in mind a bad reading from exhaust O2 can also mean a bad catalytic converter.

Problem with sudden drop in fuel mileage is it could be so many things. I try the cheap (or free) fixes first such as MAF and IAC cleaning before looking anywhere else.

[kmann]

I have a 2004 Bonneville with the 3.8 motor. I bought the car used back in August last year. I used to get 360-400 miles per tank. Recently I've noticed that I'm getting significantly less mileage per tank. Sometimes not even 300 miles in a full tank of gas. I've also noticed that from full to half tank I'm getting usual gas mileage and after half a tank the gas mileage takes nose dive.

I'm was curious if anyone else has experienced similar problems and what the problem is, so I can get it fixed?

Thanks

[Arrowhead]

It might just be your fuel level float/sender that's acting up and giving false info to the gauge and DIC. ( Just a guess, though.

This is an old thread, might be better to start a new one.