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06 Maxx SS MPG

4654 Views 28 Replies 8 Participants Last post by  Alan06
My 2006 Malibu Maxx SS (3.9L V6) is averaging 13.67 mpg. My last fill up was 11.6 mpg!
I purchased this vehicle a month ago and track my mileage on every fill up. This is not the information coming from the computer, these are my calculations based on miles driven between fill ups.
I replaced the EVAP purge valve and got a new gas cap after a code. The CEL hasn't gone off since.

Any ideas on why the vehicle is getting HORRIBLE gas mileage?
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There are tons of things that can affect MPG. The state of maintenance on the engine in general, spark plugs, O2 sensors, catalytic converters, MAF sensor, clogged intake or throttle body. What possibilities have you eliminated?
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1. Absolutely check and replace the plugs with OEM spec, you're due.
2. Open and inspect the air intake box and filter. Remove the filter and look for clogs, install new OEM paper filter if necessary.
3. Pull the MAF sensor and visually inspect the filament for crud (do NOT touch the filament, buy a dedicated touchless MAF cleaner spray).
3. Open and inspect the throttle body. Spray a rag with throttle body cleaner and thoroughly clean it out if dirty.
4. Add a bottle of techron injector cleaner to a half tank of gas and drive the car aggressively to clean out ports and injectors.

Techron injector cleaner:

CRC MAF Cleaner

CRC Throttle Body Cleaner
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If none of that works, then examine/replace the downstream O2 sensor. After that check the cats.
Change the O2 sensors also, use only AC plugs and sensors, the upstream sensors that are closest to the engine as they control fuel mixture.
Dang, I had it backwards and said downstream. I over thought it.
AC = ACDelco brand OEM parts, in case that's confusing. With rare exception, use factory parts for replacements.
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What are you basing your fuel economy estimates on? If you're using the gauge cluster average readout, have you reset it since doing all the work?
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