12 mpg update
 

So we've changed out the spark plugs, wires, and 1 coil, as my car did have a misfire, but I was planning to do it eventually, as I hoped it would lead to better mpg. And I was out of luck. Finally did a refill after getting a fresh one after changing everything, and it looks like almost exactly 13 gallons got me exactly 160 miles, which is about 12.3 mpg.

It's been 12 mpg constant for about 3 months since I got the car. Why did I drive it like that for so long? I thought it was just the way I drove because that car is so fun to drive. But now I'm spending too much on gas alone, and the price of a barrel of oil just went up too..

I investigated my low mpg by dedicating a tank of gas to very good driving with limited asswipe driving not too long ago. About 40-50 miles in, i was already down to a 3/4 tank, so with that being that crappy, I decided my dedicated tank was gone and went back to "normal" driving habits.

I believe I do smell a faint gas odor inside of the cabin, but only very faint, it's not that obvious, I think. Is a gas leak a probable cause of this horrendously low mpg?

Where would the most probable place for a leak to be at? Note: this car had been sitting in an impound yard for almost a year (sad, I know).

Please give me an idea of wth I'm looking at here. I love this car, but with the combined fuel economy and insurance costs I'm getting, I'm not sure how much longer this will last me.

Thanks.

P.S. It just occurred to me that if there was a fuel leak, I probably would NOT have passed a smog test.. So now I really have no idea at wtf is going on. :(

How's your compression? How's your catalyzer?
Did you clean the MAF\IAT sensor?

I have no idea for all of those.. And have only come across compression once, and I asked my dad about it, who asked me what the point of that was, because if I had low compression, then I'd need a new engine.. And I'd hate to resolve to that. I have no time or money to do that

Well, if you plan on keeping the car and want to resolve the fuel consumption problem, then the items mentioned by bse50 would be very likely causes. So, you can either get it checked out and fix what is needed, or live with the fuel consumption. But keep in mind, not resolving the issue may have worse consequences for your motor later on. You do realize that if the motor is low on compression, or if the catalytic converter is faulty, you may be eligible for a replacement under warranty... right?

If you can't afford the time or money to maintain it, maybe it's time to consider other transportation...

Yep, ignoring the problem will never be a solution.
In the end it is the OP's fault so he has to blame himself for not checking those things prior to the purchase.

Given that the car was in an impound yard for a year I think that he is no longer eligible for a warranty claim. Doesn't the manual state that you have to respect a mileage\timeframe for the maintenance to be done, whatever comes first? :)

Get a compression test done and check what we told you to or just sell the car and buy a beater you can afford. Just because you can buy a rotary for dirt cheap doesn't mean that it is a cheap car to maintain (well it is, if you do it right).

Ah, now I see. And he only paid $5,000 for it. Well then, this might come under the heading of "you don't get something for nothing".

An '04 automatic with over 80,000 miles on it and no maintenance history might be on borrowed time. The catalyst might still be covered under the emissions warranty though...

I've seen this happen at least a dozen times here too.
Buy the car cheap, cry when you see the repair bill to make it perform again as new.

It is also worth noting...that depending on how you drive the RX8...13mpg might be what you should expect and there might be nothing wrong at all. Find a nice group of locals to help you out would be the best thing you could do.

Warranty on the cat is 8yrs/80k miles. It looks like your out of luck there. The warranty on the engine core is 8/100k miles, so if your engine has low compression it will be replaced by Mazda.

I'd like to note that under normal driving, I get about 55 miles on the first 1/4 tank and then like 75 on the second 1/4 tank. It's not the same across the board (in other words the fuel gauge is not accurate by the 1/4 tank).

While 40-50 is a little low, you need to go a full tank of gas test (if you have the patience for it). You still definitely have a problem, but 'going back to normal driving' after 1/4 tank tells you nothing. I can drive pedal to the metal and still get around 15-16 and very easy driving still only yields 19 max.

If you have a bad or clogged cat, every time you drive and especially every time you high rev, you can be slowly ruining your engine. It puts back pressure on your engine and you will blow a seal, definitely requiring a replacement, that may or may not fall under warranty if they determine it was abuse that caused it. (Not fixing a known issue is abuse).

I see, this is very valuable information.. FYI the price was 10k, but I bartered it down.. But since I bought if off of a lot, would I still be good for the warranty on the engine core? I currently have 84k miles.. theres a reputable mazda shop that is half a mile from my house, really nice owner.. or should i go to an actual mazda dealership?

Yes

thanks ^ and I don't care what I pay to fix it, as long as it's happy mpg comes back, but about how much should I expect something like the above cost? And about the 100k engine core warranty, what if they disregard that or don't apply it for my car? Or is it universal no matter?

I'm new to warranty stuff.. And would have had a bad experience in my old car if it were still under warranty, because chrysler was saying no to engine replacements on it's faulty 2.7L engine installed in the sebrings

"Happy mpg" ???

anything better than 12 city/13 hwy. However, my mom did point out an article to me about the winter gas mixture they have now, and people have seen lower mpg than they usually have.. But 3 months ago it was hot weather, it has to be something else

But you're only supposed to get 18mpg on average, 16 if you are primarily city. You could easily be doing 12 just by driving style.

Go take it to the dealer to get a compression test , buy the other 3 coils u need to replaceed all of them and buy a catless midpipe......

well aware my mpg can be greatly affected by my driving style. But it's hard to explain driving on the highway at 60 mph drafting my buddy in his 76 blazer who was draftin a tanker, and still going down to a 3/4 tank in 50-60 miles.. But yes, I will probably stop by a dealer tonight after work

Go to a Mazda dealership and get them to do a compression test, just like everyone has said. You're SOL for your cat, and OEM is pricey...
A compression test will run you anywhere from $150-200.
Cleaning your MAF is easy. Check the "First $100" thread

Good luck man

regarding the compression test: what good will that do? Just tell me if my engine is worn out or not?

pretty much. But, that will be your grounds for submitting for a new engine!

Im going to disagree with everyone here and say a compression test is not worth the money for your car. If you had a compression issue you would be noticing a lack of power among other things. When I first got my 8 I would get 12 - 14mpg because I was driving it like any other stick shift car. Once I changed my driving habits and learned more about the rotary engine I figured out why my mileage sucked. Then I got it up to 16mpg city before getting a tune from Jeff so I now can easily do 18 - 20mpg. You changing out 1 coil shows how much you really don't understand about the engine and how it operates. Sure...go drop the $2K by taking it to the dealer and getting a seafoam treatment, a new cat and a compression test. But I'm tellin ya...it's more than like how you are driving...but if it isn't it's cheaper and easier to drop the $200 on a midpipe and $400 on good coils and $5 on SeaFoam.

oh I understand now. So I'd just be better off checking the other things out first before doing all of that then.. I have read some really old threads lately and they were talking about an ecu flash gave them better mpg.. And I have no idea about my car's past, so could they have missed that? The only thing I know what they were doing was trying to be shady, as they removed the license plate light and blocked the driver door light somehow

what's wrong with changing just 1 coil? I have no idea if that was even the problem. But we got all the sparks and new wires in.. I see no difference in mpg. And I don't really feel any lack in power.. Unless low power in this car is more power than my normal operating old car? I find it weird putting the pedal all the way down at a stop on a rainy day won't even spin my tires at least.. But I realize this car has low torque at higher rpms

The OP may or may not know if he's experiencing a lack of power as he is new to the engine.
The fact that you're still under warranty to me justifies getting the compression test. A new motor far outweigh the benefits of replacing coils and exhaust mods...

Our cars run pig rich from the factory...so the Racing Beat Flash and the MazdaManiac AccessPort Tune do provide for a better mpg. This is also why you hear people say to drive the car like you stole it. Higher RPM ranges provide more air to fuel which in turn helps your gas mileage.