lgilbert50

iTrader: (1)

No, slightly modified, exhaust, ignition and remap of the ECU (Best mod thanks to Mazdamaniac.)

thewatcher101

I got an extra 2 mpg using a 09 tranny.........only 375 fill up and i can break even

sweatr

I can see where RIWWP has a point about MPG being important in respect to being a barometer of sorts. I do track mine every tank. The MPG varies on a lot of things, so as long as I am getting 210 or more per tank full I feel ok about it. I drive mine pretty hard, I hear the warning bell several time per time I drive it so I am not worried about MPG per say.

MrEd2

speed still bugs me. I do a work circuit between fill ups, always 220 miles, 90% open freeway in S-II manual. If I drive mostly below 74 mph, I use ~11.4 gallons, 74+? ~10.6. If I drive 60, I still use 11+. There seems to be no way to maximize fuel economy when cruising below 3850 RPMs. Slowing down doesn't appear to matter. Wish this had a instant mileage readout like the Mazda3

sweatr

At the end of the day the 8 isn't any kind of high MPG car, it's just for fun.

AlShinka

Is it possible to make the Rx8 more efficient( fuel mixture adjustment etc.) via a tuner like cobb AP?

sweatr

This is true.

phantom257

Hey all, since this is trouble shooting have low mpg that i have done all i can (almost) to correct it and still to no avail.

from riwwp post:
- coils -BHR NEW
- plug wires -BHR NEW
- plugs- CORRECT NGKs NEW
- engine compression - ENGINE NEW/mazda 700 miles on it
- Front O2 sensor- DEALER check and graphed good
- Rear O2 sensor-DEALER check and graphed good
- clogged cat- DEALER check and graphed good and inspected twice
- clogged air filter- NEW OEM paper style
- engine block grounds- Unkown after new engine install
- fuel trims- Reset
- vacuum leak- NONE dealer and personally checked and tested
- MAF fouling- CHECK graphed good at dealer, is clean
- ESS fouling- clean and 100% on data from dealer
- brake pads dragging- not dragging
- tire pressures far too low- 32-40 no difference
- engine coolant temps at cruise- measured at dealer and my self multpiple times, normal
- Driving style- Easy break in, also hard driven on old motor no differences

so with all those already covered here is what i have, bought car used as the second owner, car had 8-10 mpg since day one, i did many of the normal checks and tests (from reading the forums and tsb's here, thank you) over the course of 7 months. decided to do the last one and get bhr ign and wires new plugs etc.. car smoked a ton when i did all these took off after the work and CEL flashed and shut down. took it in dealer tested and engine barely failed tests so i got the new warranty engine (a reman from reading here i guess) i also had new rear end, trans, fluid done at that time. new clutch oem. after getting it back and driving it for about 700 miles the mileage is no longer 8-10 has gone to 10-11. according to everything i read this indicates there is still a problem.....

i drive 95% city i go about 12 miles each day on average driven every single day no exceptions. i have driven it nice (under 5k) and hard not much difference. this is based on 12.8-13.3 gallons getting 119-145 miles measured over the course of 8 months. Dealer left me scratching my head, i am an experinced auto tech with non of my tools they are in another state atm... dealer suggests the ethanol is the reason ie poor fuel is all i have to go on? is the premix the solution to that or an additive package? or any other thoughts suggestions?

not getting another car... this is not a complaint about mpg this is a serious inquiry as to what i should check or try to get the mpg most others avg in a city. just trying to figure out if something else is wrong. if it only ever gets this mpg i will be fine with it as i love to drive it every day.

driven in NH, cold or hot sun, rain, snow. i let it run about 20-45 secs before i drive it out, nothing over 4k until at operating temp.

RIWWP

iTrader: (2)

The problem is likely due to the following points:

1) As you have ~95% city driving, your mileage is only about 3-4mpg too low, rather than 9-11mpg too low. A 25% gap to close.

2) I assume your 12miles per day average is not in single trips per day, but at least 2 trips. With such short trips, you are spending a rather large portion of your trip below normal operating temperature. Under ~160f coolant temp, the ECU is adding quite a bit more fuel than when above it (the source of the extra fuel that causes the infamous flooding). You could idle longer, though this will have it's own fuel penalty that would offset the gains of a larger percentage of miles in operation temp.

3) Your engine is not even broken in yet. 1,000 miles is the standard, but even then, many people believe the rotary still hasn't broken in until around 6,000 miles. Your engine still isn't sealing as ideally as it can be yet.

phantom257

yes your assumtion is correct 2 trips each short. i tried letting it warm as well you are right it has its own penalties for gas use. as for break in i thought of that, but i just had to make the inquiry. thanks for the good response, i am thankful. i will finish the break-in and monitor, so i will have more data in a few months.
thanks.

GK1707

iTrader: (10)

Sounds about spot on .. I get the exact same MPG all city driving. Usually anywhere from 100-150 miles per tank. Ignition system still new and all sensors checked out to be functional. The 8s not a great city car, kinda just gotta live with it.

lgilbert50

iTrader: (1)

Ditto for me in the city.
06 Shinka

phantom257

thanks guys, just really wanted to check as i said did a ton of research and really thought something was still off, still going to look for a better fuel station and try premix after the 1k mark.

as for living with it... i am used to an old 1970 ford truck i know all about 8 mpg this is just more fun by 100 times. LOL

sweatr

My gas mileage went up a good bit when I started premixing. My last tank I went 260 miles and prior to premix I got around 220 a tank, but that is mixed city and freeway so the only thing I know for sure is that my MPG increased. I am on my 3 rd tank full/w premix. Best of luck.

mono4lamar

All stock and 240 a tank.

beeker100

All I know is the car get terrible gas mileage. It is purpose built.. to run high RPM. If we wanted gas mileage, we wouldn't be driving RX-8's.

cpet

This cars gas mileage isn't as bad as everyone has led me to believe.

Bought the car with 22,097 miles and a full tank. Filled up when the orange light came on and that put 14.227 gallons in her tank. It's a 15.9 gallon tank so I just did the math. Filled her up for the first time at 22,354.

So I got 257 miles before the orange light came on and that was with 1.673 gallons still in the tank.

My Mitsubishi Eclipse wasn't getting that much!

I'm going to keep track of the milage and maybe try chevron vs shell. I stopped using BP when they had that spill. I should have never trusted BP anyway as they aren't top tier gas. They weren't for years anyway.

That was with a mix of city and hwy driving.

djfa

iTrader: (3)

you're one of the lucky ones, I do mostly highway driving and I get around 200 miles to the light. The car has just a little under 100k and I never had a tank over 215 miles to the light! I wish I could do 260+ like you it would make me want to keep the car a little longer. Im going to get rid of it this year and get something that consumes 66% less in gas. The saving alone is gas will be half the monthly car payment. LoLz

RotaryP7

I'm pretty much 70/30 highway during the week. I did try to push it last week. I actually hit 299.9 (lol) I could of probably gone over 300 but didn't want to risk it. My best.

J8635621

iTrader: (10)

Damn I hit over 300 miles at a half tank in my DD and it has a smaller tank lol. And it has more torque. It isn't as much fun though and I can't pick up chicks as easy.

To not be entirely off topic, I routinely hit 320 per tank in the 8 before I moved to Houston.

RIWWP

iTrader: (2)

Luck doesn't have much to do with it. If you can't get ~280 miles over the 13.1 gallons will the light with highway miles, there is either something wrong with your car and it's entirely fixable, or it's something wrong with how you drive, which is also fixable.

djfa

iTrader: (3)

Ok so let's go over what could be wrong. First off we can eliminate ignition system as my coils plugs wires are changed every year. My engine is a year old, healthy and gets the same mileage as the old one. Air filter is always clean as well as ESS and MAF. Tire pressure is 33. I can also assure you that aside from my daily redline I usually shift around 4k ish and try to drive/coast above 3k.


Now Im running an AP midpipe with mazdaspeed exhaust but I was told that it doesn't affect mpg numerous times on these threads. So what's left? Faulty injectors? Front O2 sensor would be a hunch? my car has 100k miles and it's an 04. If I could somehow consistently get over 200 miles a tank, I would consider keeping my ride. But my salary is getting less and gas is getting more expensive!


Do you think it's worth investing in a new O2 sensor? I went to the dealer once with this mpg issue and they told me everybody gets the same mpg and sent me on my way with 1 hour labor of 109.99

gendry

Stock here and I am lucky to get ~250 per tank

Edit to clarify after I did some calculations: I usually get between 150 and 200 per tank. 250 is in best conditions possible and is rare. I drive in a lot of traffic and tend to have a heavy foot though.

I recently cleaned my MAF and it didn't seem to change anything

car5car

MPG of automatic tr. cars can be improved by reprogramming gear switching points.
Cars with wideband O2 sensors can be reprogrammed to run leaner.
Do 04 RXs have wideband sensors?

dodoman

21 mpg? sounds way too ideal, I thought the average with 50/50 city/highway was around 16mpg