Blue87Sport

If you're cruising, then you're in closed loop mode. The ECU will determine the amount of fuel to inject based on the O2 readings. Whether it uses one or two injectors is irrelevant, the amount of fuel is the same. So there's no significant fuel efficiency differences at just under 3750 vs just over it. The only difference is that higher speed = more drag which results in higher fuel consumption.

For everyone telling him to redline it, remember he just got the car and is still in his break-in period. Take it easy for the first 600 miles and then let it unwind. Think of it as foreplay.

Foamy

I am getting the distinct feeling that something might be wrong with my motor, less than 6 - 10 MPG is just ridiculous, and on a long trip 19 mpg was the most I ever got.
One thing I should mention about my warm ups, most of the time the temp gauge needle has hardly moved (Note most mornings here are 10 - 20F even in my garage), and I know the motor is not fully warmed because the revs are limited - so I don't think I am idling for and excessive amount of time.
With all that said I stilll love the lively performance of the RX8 and did not get the car for fuel economy.
Does anyone know if the repair shop can test for something that would lead to high fuel consumption? It's due for a service in a couple of weeks any advice on what to ask them to look for will be appreciated - Thanks.

zoom44

they can run many tests for operation status and fuel consumption but you will have to leave your car with them for many days and they might make you pay for the diagnostic work.

tell us how you calculate your mpg.

yiksing

I keep hearig about this closed loop and open loop but still had no idea how it works, should I just search or can you just share some summary of what it is?

Anyway there are two beliefs regarding break-in, one is baby it and the other is thrash it.

rx8wannahave

Really....has this been proven or who said this works this way? I would like more information on this also.

Foamy, have the car checked out but again I just don't think you need to leave your car idle for such a long time in the morning. You will warm it up faster by driving it. 1 minute tops should be enough.

Foamy

Hi Zoom44 - in answer to your question on how I calculate mpg;
Typically I let my fuel run down to about 1/4 full, then fill it right up, noting the amount (11 gals usually) and the odometer reading. Then drive the car until again I get to about 1/4 full. Note the odometer and fill right up again. The miles driven divided by the amount of fuel required to fill up is the mpg for this cycle. I have done this at every fill up since new (Sept 04) and I have it on a spread sheet. (Would attach it if I new how ?).
RX8wannahave - If I limit idle to one minute I would be in trouble as the car is not warm enough.
I know this because when I push the gas the car speed is slow and there is that strange "woomping" sound from the engine and it goes slowly because of the RPM limiter at low engine temp- Whamm some one rear ends me.

max5roadster

Odd^ I have given 0 warm-up time before, but kept the revs under 2.7k-3k and slowly accelerate with no engine sounds or ECU interference.

DarkBrew

My warmup is always just until the idle is down to 1500 RPM and then I stay below 4000 RPM until the temp is up and don't thrash it until it is fully warm. I average a bit over 17 US MPG in mixed Canadian winter driving.
I have not had drivability issues even when cold other that the shifting issue.

rx8wannahave

Hmmm, like stated once the RPM's hit 1.5K you should take off. At that point you shouldn't have any issue with the engine. Now, it will still keep you under certain RPM's but remember you shouldn't be revving high when the engine is cold anyway. Heck...once it's at operating temperatures you should still wait a bit longer before pushing it to higher rpm's.

I honestly don't have experience with negative temp's (0 in NY is the coldest I’ve felt) but it's gotten to 35 here before and I know it takes a bit longer before I start driving the 8 but again 5-10 minutes just sounds excessive to me.

Once your rpm's fall to 1.5K...take off. Try that and see what happens…and then let us know.

You know if there is an engine that needs an engine block heater, it's the rotary.

Blue87Sport

Well, by definition, closed loop means the ECU reads the signal from the O2 sensor and adjusts fuel to reach a target AFR. See http://www.autoshop101.com/forms/h44.pdf for good background information.

So the question is whether the ECU is in closed loop or open loop when cruising. From the information posted by experts like Mazdamaniac, Rotarygod, Rasputin and others, as seen in threads like https://www.rx8club.com/showthread.php?t=53406 and https://www.rx8club.com/series-i-tech-garage-22/why-wide-band-oxygen-sensor-rx8-64509/ it appears that with the coolant temp > 130F, throttle load <35%, engine RPMs < 5500 and constant speed, the ECU will be closed loop mode. In fact, running with cruise control on is the ideal condition for closed loop operation.

I'm sure someone with a CAN bus scanning tool could verify this.

Nopstnz

The warm up time had puzzled me for a long time. I assumed that I was supposed to do what the dealer said and let her warm up for 2-3 min before leaving. But I soon got really tired of this and most people on here seem to agree to the 1 minute or less warm up time. I wanted to see what the dealer had to say again and after clarifying a simple question many times the guy said, "No, no warm up time is necessary, as long as it is not shut off cold. He really knew the part about shutting it off cold but not the part about the warm up. So, in order for better fuel mileage and a feeling of being "safe" I'm gonna let her warm up for about a minute or less. This works out well too because it's enough time to put the seat belt on, find a good song on the ipod, then throw it in gear.

It might be an interesting idea to call other dealers and see what their opinions are...

LiveBlues

My typical 8 day goes like this. I let my 8 warm up for ~5 minutes before I leave for work in the morning. When I leave my house, I drive about 3 blocks before I have to enter the highway. At that point, I need all the power I can get usually. I typically redline it twice at that point. Between the 5 minute idle and a couple of redlines, I still get around 19 mpg all city.

Like Whoa

125F to be exact
open loop condition when engines cold, hard accel, wot, & decel

zoom44

good - we have some people in the past who did not calculate properly. they would run it down to the ligth came on or whatever fill up and then use gallons for an entire tank instead of the amount of the fill. so im glad you have that straight

the rest of that- "woomping sound" car wont speed up so people rear end you... thats really somethign i cant fathom. the rpm limiter when cold is about 6- 65 k rpm. that is plenty of rpm to get you to what ever speed you need. i seem to hav emissed any previous mention of womping- can you go over that again?

im thinking you have a clogged cat btw. no air out =no power= bad gas mileage.

zoom44

on decel- the car actually cuts fuel injection. afr goes to like 20!

Raptor75

This is the only real problem with this can for me. Performance is good, looks are great, ride is great but MPG is bad and Mazda is doing nothing to fix it.

I get 11 to 12mpg city driving very conservatively, Highway is around 17mpg, other RXs are getting much better why? I'm bringing the car in next week but from all I've read the dealer will not do much if a flash and spark plug change don't fix it. They will write it off as driving style and dismiss me, which is bull.

I read all the posts before buying and expect 15mpg which I thought was bad but at least I bought it with this lower expectation, then I get 11 to 12mpg. I have only read of two people on this board who had their mpg increased after a visit to the dealer so I am not optimistic. I have read of dozens who have been turned away by Mazda and told to live with it.

Now lets look what Mazda's in action has cost them, one potentially loyal customer disgruntled and feeling abandoned. Every person that this individuals talks to about his RX is warned about the dismal fuel mileage and lack of resolution by Mazda, those people walk away from the RX after hearing of the problems and the word spreads. Mazda's RX sales are down and we wonder why.

I know this is a recurring complaint but it really pisses me off that Mazda know there is a problem but has no resolution.

yiksing

We shouldn't use oil consumption on piston engine as a benchmark for one on rotary engine.

Foamy

Hi Zoom44 - the "woomping sound" and speed limitation is bit like throttle is open but fuel and air to the engine is being strangled, at least that's what goes through my mind when it happens. RPM's are definitely limited to much lower than the 6k you mention, lucky to get above 2.5k.
This sympton goes away very quickly, maybe 1/4 mile driving and it only happens when it is really cold < 20F.
I called a new Mazda place today and they are going to look over my car next week, I mentioned possible clogged Cat' they said most unlikely if I did not have a check engine light and performance would be very poor at any temperature.
Will let you know what they find (If anything)

Foamy

At the risk of beating this subject to death - does anyone have a reliable technical explanation why the RX8 rotary engine gets such low mpg compared to a "Similar" piston powered sports car.
Also, to be specific why at idle does the fuel consumption appears to be significantly higher than a piston engine at idle, is this true ?? it certainly seems to a factor.

bao0518

i just got the car and i get about 14.5 mpg. that jusk suck too