Ledfoot

Thanks for the heads-up Go48! I haven't gotten through all the TSB reports yet, but I'm certainly trying. It's a lot easier learning about them here than when I had to go through the same deal with the S2000.... The reports for the first two model years of that car look like something a NASA computer might spit out... No joke!

Looking forward to my first brand new car!

Go48

You're certainly welcome. And when you do get the car, you might consider joining us at the Mazda Sportscar Club of Washington (www.mscw.com or maybe it's org). It's a great club with a variety of activities ranging from autocross to scenic tours to shows.

Ledfoot

Wow...checked out MSCW... I'll definitely join! Your next couple of meets are at Tysons....five minutes from my front door!

Go48

Yeah, that's why I suggested that you check them out. Unfortunately, I'm nearly 2 hours away from Tysons so I don't attend the meetings.

Raptor75

I have a new 05 (8/05 build date) with about 400 miles on it. With 90% city driving I get about 12.5 mpg. Very poor, was expecting 15 to 17mpg. I have been doing a lot of reading and feel the most likely cause of some RX-8s that rate so poor could be as follows.

1) Thermostat: could cause trouble but I think it would be rare.
2) Catalytic converter clogged: Maybe but I would expect poor performance to go with it.
3) Engine Compression: Easy check and performance would suffer
4) Bad MAFs: This I feel holds real promise, I understand that the MAFs in the RX-8 can have a wide difference in voltage from car to car. If the air density is miss reported so would the gas delivery…true?

Has any one here with bad mpg ever switched their MAF with a RX-8 with good mileage to see the effect on both cars?

zoom44

ive seen 2 bad tstats and only one bad MAF. lots of dirty MAFs tho.. the voltage difference is highly overstated and not something to even bother about. we're talking a difference of .01v between some (not many) cars(less than a oily dirty MAF) which could be a result of inaccurate rpm readings. that will not translate into a huge mpg disparity.

what will is 1 car staying in open loop while others are in closed loop. this makes the car look at a table for its AFR and will keep the AFR in the 12s or 13s instead of hunting for 14.7 like it does in closed loop.

compression dropping may not be felt at all. might show in a dyno if you dyno often. but it could cause mpg losses well before its felt in performance.

Raptor75

What is the tstats?

I thought open and close loop transition was at a preset event (rmp/ throttle setting etc...) would not all cars transition the same. If not what controls the transition?

Also how dose the car determine what the accrual real time AFR is, I believe the 02 sensors tell the computer this. If this is the case could there be discrepancies between 02 sensors misreporting the AFR?

agoodcave

Raptor,
How much time is spent sitting at lights/traffic. To improve your milage, take a long trek by freeway or better yet, back roads. I get 17-18 mpg in the city but its not a lot of sitting in traffic. What shocked me was country road mountain driving I got over 20mpg and never let the tach fall below 4K. Idling just sucks gas on this engine.

Mike

zoom44

Thermostat. when you start the engine the car stay in Open Loop until it is warmed up. It then switches to Closed Loop until the Load/RPM transition that is programmed into the PCM. If you have a bad T(hermo)stat then the PCM never goes into Closed Loop.

If there was an issue with your O2 sensor your PCM would tell you by lighting a CEL. It compares BOTH O2 sensors against other information to determine if they are working correctly.

Raptor75

My city driving is suburban city driving. Drive for 2 to 5 blocks sit at a light for about 7 miles to work then back home another 7 miles. Chicago weather 32 lately. I’ll be doing a long Highway drive soon.

Zoom44,
What would be signs of a stuck t-stat? My car takes about 7 minutes to warm up but the inside of the car take over 15 minutes to start getting warm air. Is this normal? My temp gauge reads a notch below half way once warmed up.

What is your gut feeling as to the large discrepancy between cars?

Cooder

Are you warming up the car in the mornings?

RX8PDX

This I have noticed has been killing mine lately.

I can almost watch the needle go down as I sit there and shiver.

Cooder

Exactly, if it's "only" around 30 degrees F, don't bother warming up. Start it for 15 seconds and go, but go real light on the throttle until the car warms up in about 5 minutes.

Raptor, you said you were doing mostly city driving. That tells me you are doing many, many startups over a single tank (as opposed to doing one or a couple of startups for a long distance trip at least 300 miles). As I mentioned before, the more startups you do, the lower your mpg. This is a factor that no one else has really mentioned. In fact, mpg falls quickly over many startups, even if you don't warm up the car. Now imagine what it would do to someone who is warming his car during all those startups! Even 10 to 15 startups will bring you down real good. I bet you are doing at least twice as many for city driving over one tank of gas.

Raptor75

Only about a minute then driving below 4k till warmed up. Engine warms up in about 6-7 min.

Raptor75

I think you are right cooder but based on what I'm reading there are other who do similar driving and are getting much better mileage. I'm looking into setting up a mpg tracking web site that will go into far more detail on driving habits, temp, distances then is possible with the simple pole method here. I hope to get a clearer picture of the RX-8 gas consumption.

zoom44

ONE IS BAD GAS MILEAGE

My gut feeling is the disparity is caused by 3 things-

1. amount of short trips. those trips around the block for lunch KILL mpg
2. short mileage/long time daily trips. going 7miles sounds short but if it takes 30 minuted thats alot of time not going anywhere. car gulps gas at idle
3. not shifting. people spend alot of time in 2nd and 3rd gear whenthey should be in 5th and 6th. you can be in 6th at 42mph. for fuel efficiencey you should be. thats why the shift points suggested in the owners manual are the way they are.

then there are the people who actually have a problem my gut on these is

1.bad Tstat
2.bad plugs
3. bad cat

warming and not moving for more than a minute is a waste of time and fuel

zoom44

data gathering https://www.rx8club.com/showthread.p...ht=statistical


results

https://www.rx8club.com/showthread.p...ht=statistical

Raptor75

This is just what I was looking for, There should be an area on this board that holds all this related info. A lot of what I was looking for I find exists but it is not always easily found on searches.

Thanks agian, you've been very helpful.

Animagix

mazda techs are driving my car around right now because i complained about poor gas mileage (13mpg) to see for themselves. =/

Not sure if anything could possibly done but, I've gotten those figures with fairly conservative driving all year round. =/

willsrx

I am averaging a little less than 10 mpg, I have less than 600 miles on my car and I am shifting before 3,750 rpms to try to conserve fuel. I hope the mileage gets better, I was hoping to get between 17-20 mpgs. I was getting that on my wrx that I traded in.

zenmoused

Yeah I hear you guys. I'm at 2300 miles, and the best I've averaged has been 14 mpg. I have driven conservatively for a couple tanks, and have gotten no more than 200 miles before the empty light. I haven't done my inaugeral oil and tranny/diff fluid change yet, so perhaps that will help a little. I dunno, I keep hoping the saying about rotarys getting better as they age is true, but right now I'm filling up every couple days. Ouch.

zenmoused

Is there any kind of formal complaint customers can make to Mazda for their 18/24 estimates? I've spent two entire tanks on a 400 mile trip, with cruise control on, no a/c. I would say those estimates are a tad bogus.

Animagix

so my gas light came on after 200 miles of driving, I go fill it up and only managed to put in 12.8 gallons to fill it up... is the car that paranoid of the fuel tank despite having 3.1 gallons left? i should theoretically get 40-60 more miles of driving. would be nice to break 200 with all city driving without having the fear of running out of fuel so soon.

willsrx

my empty light went on at 195 then I could only get 13.25 gallons in, I guess there was about 2.65 gallons left. Anyway I tried 89 octane this fillup and I am at 122.5 at my half tank line. I am usually at 100 miles with premium, plus my tailpipes are not black. I did not really notice a change in performance when I got on it.

jammiman

Ok,

I just filled up my tank this morning, and I got 114.5 miles on the last tank! If this is a 14 gallon tank, then I am getting 8.1 MPG! This is the lowest that I have seen on any thread? What should I do? Also, does downshifting or "engine braking" burn gas in a rotary? I can't see what I am doing wrong. The car has 32000 on it, and they are all city miles. I drive it moderately hard, but nothing crazy?! Whats up mazda? I love the car, but my Ram 3200 gets better mileage!