I havé a 2007 rx8. I know what everyone says, rx8 are not good on gas what do you expect, yet i’m getting barely 170 miles in a full tank of gas, and I understand that I do lots of city driving and it’s not like I drive the most economically, but a full tank city driving is at least supposed to be 270, where are those extra 100 miles going? Now I have run compression tests, all is good, car is never winter driven, cold starts are all done well, new spark plugs, i have a cat delete, no misfires; a lot of backfires i get though, though i don’t see this as a bad thing, car has 114k km which is about 71k miles. But the car really is mint and has never tasted regular gasoline
Could it be;
-ignition coils
-fuel line leak
-bad compression
-something i’m not aware of
Please, I’m in dire need of guidance

 

I barely got over 200 miles a tank driving mostly on interstate highways.
It's possible with mostly city driving to get less.

 

Kosta, I've never gotten 270 mi on a tank even all hwy driving. So, that m/b a bit unrealistic. Yes, coils, compression ,or a fuel line leak could contribute to poor mileage.

- Test the coils w/ an HEI tester
- you said you tested compression. What was the result?
- Do you smell or see signs, e.g. a pool, of leaking fuel?

Additionally, have you had the fuel pump retainer ring recall done? I recently saw a sudden and significant decline in fuel economy. Ultimately it was being caused by a crack in the passenger side retainer ring, which was only discernible by poor fuel economy and a fuel leak ONLY immediately after a fresh fillup. So, fill her up and check for leaks. Check out my build thread for pics if you like, Curt's Gr8t 8 Turbo Build.

 

I get 270miles (300 sometimes) on a 'tank' (14.5 gallons) with open road cruising no problem at all ...but around town that can drop to 180-190miles. A 'tank' is not a unit of measure BTW and everybody's interpretation of that can be different. How many gallons?

 

I double checked my mileage over time (boosted):
- ~ 260 mi: (best) during road trips...all highway
- ~ 225 mi: normal daily city driving.

Edit:

1. Also the two tank capacities s/b noted:2. Given the fuel capacities above...my range is definitely farther ...as my fillups never exceed ~13.5 gal. Therefore, I estimate I'd achieve ~ 260 city / ~300 hwy mpg ...were I willing to run her tank to near bone dry. Nah.

 

Could it be ignition coils? Yes. Very likely.
If you don't know how old they are, replace them. 25-30k miles is what you should expect from stock coils.

 

Same here on 2 different NA RX8s. Identical numbers in fact.

 

Not sure where the backfires are coming from. Not normal on stock tune/well running stock car in my experience, with no cat.

 

Look (see) harder. Backfires are unburnt fuel in the exhaust lighting off. If you backfire at all, it indicates a poor tune. If you backfire a lot, you've got a complete garbage tune. You're dumping fuel out the tailpipe, and that's where your 100 miles of range went. Exact same thing as diesel bros "rolling coal".

 

I usually get 17mpg whether I'm in the city or cross-country; doesn't matter if I'm driving like I stole it or like an old man. I'd consider plugs, wires, coils in that order.

 

Yes and no… I speak with not having a cat, it could be throwing off the amount of fuel being used by the ecu. If you have a check engine light and pull the numbers that may answer your question. I can honestly say if your looking to improve fuel mileage do the necessary preventative maintenance possible with up to date parts as needed. Stay on your ignition and fuel system parts, After that you should consider an upgrade to your ecu. I can only speak on the platform of Versatune, it has saved me miles per gallon depending on the tune I flash. If you purchase there lite version you have a tune that is economical and uses less fuel, granted your car is close to stock. They state on there forum that the Ecu in the RX8 is naturally setup to be too rich. I run a tune with upgrades to coils, no cat and catback and I will get anywhere from 200-225 mpg

 

I ws getting very good mpg. 18 - 19 city, and 22 on hwy. However, i ran fuel cleaner recently. It improved the performance a !ittle and the exhaust is a little louder. Wondering if it cleaned out the CAT a little. However the gas mileage diminished to 16 mpg. Havent done hwy driving yet.