At the risk of being flamed into a smoldering little burnt marshmallow......

What would be your best educated guess as to why some of our RX-8 get very poor mileage. I'm talking around 12mpg mark and I'm ruling out a drivers lead foot. I'm looking for why one car get 17mpg while a similarly driven RX gets 12mpg.

I am wounding if it could be a sensor sending incorrect info so the car uses too much fuel. Any info. on how the main computer decides how much fuel to use would also be appreciated. I was thinking about the engine itself but if the compression ratio is OK and there no obvious signs of trouble I ruled it out. From every thing I have read I feel it is the main computer.

You guys are my starting point on what my turn into a fruitless trip.

 

bad Tstat. check that first. a quick search for low mpg posts turne dup this list from some guy named zoom44 https://www.rx8club.com/search.php?searchid=1230071

add dirty MAF to that list

search for a thread about open and closed loop fueling for the info on how the car knows how much fuel to use.

 

Just wondering, why are you rulling out the drivers lead foot?
There are probably a variety of reasons why the 8 gets such crappy mileage, and a combination of these factors probably lead to the inconsistent mileage from different drivers/cars...
ill add to that list zoom put up...
1. "drivers lead foot" as you say you ruled out, but still a factor nonetheless
2. The car itself runs pretty rich anyways
3. Shot distance trips
4. Stop and go trips (heavy traffic/city)
5. Some people still idle in the morning to warm up the car
6. Newer cars seem to get worse mileage

 

I myself have driven the car gently and seen 12mpg so when I see others say the same I believe it. Likewise I have seen others say they hammer the car and get 17/18mpg. Because of these I feel safe in saying that thee is just something wrong with some RX-8. If you take a look at it like this you will quickly rule out most of your reasons.

There is something wrong here and I'm just trying to find out what it could be.

 

Thanks zoomer I'll read up on it.

 

I would suggest you drive with another RX8 owner who gets "normal" or better mileage on his/her car. You can go to a Chicago RX8 meet when they want to do a driving trip. You could swap cars or even have another owner hop a ride in your car (except you let him drive your car), and then calculate mileage.

I have thought about this before and this is the only solution I was able to come up with.

 

The car is new about 400 miles, so it is far from broken in but I have heard from others who are getting 17mpg right off the show room floor. I need to understand how similar cars that are driven similarly get such varied mpg.

I'm getting ready to bring it into the dealer and knowledge is power. Sometimes the search can be a problem if you don't know what to search for so even if people point me in the right direction it is appreciated. I could also be looking for a silver bullet that no one knows how to find.

As for the post about meeting up with other users, I have already gotten on the Chicago users group mail list so I hope to leverage their experience in the next few months.

 

My first tank from the dealership was a little over 20.57 mpg but I can't be sure the dealership filled it up all the way. Second tanks was 18.78. Third was 20.06.

 

41k miles 18mpg low 24mpg hi. ~21 ave.

beers

 

32K miles .......7mpg low Track!
22MPG High 14.8 Av

I drive 10 miles to and from work...stop and go.....get poor mileage
Plus I have a lead foot

 

We have a running thread about this in Issues & Problems.