RETed

That's the problem...you can't.

The Mazda rotary engine is an engineering marvel, *but* fuel economy is not one of it's strong point, period.

Due to the inherent design of the motor, fuel efficiency is not one of it's strong suits.
This is due to mainly...
1) The long, rectangular combustion chamber which cannot burn as completely like a multi-valve piston engine (which is round), and...
2) The aggressive exhaust port timing which ends up shooting a lot of the combustion forces out the exhaust.

If you baby your driving, you might gain 1 - 2mpg.
Running more air in your tires might gain another 1 - 2mpg; the downside is that you might end up prematurely wearing your tires (in the centers).
As Cybaster mentioned, a CDI box might get you another 1 - 2mpg; other will argue the CDI does nothing, and one real downside is that it eats spark plugs faster.

Driving all freeway miles will easily bump up mileage over 20mpg.
But this means you will usually end up filling up gas twice as fast!
So it's end up being a matter of $ / day and not miles / gallon...

If you're stuck doing "city" driving, you'd be hard pressed to get 20mpg on any 13B.

Bottom line, you're not going to significantly raise your mileage.
If you try some of the tricks mentioned above, you risk wearing other parts of the car faster.

I would seriously recommend you get another daily driving and get rid of the FC if mileage is a primary concern.

That's the long version of my answer.
You would've found all of this info posted if you did a proper search.


-Ted

RETed

The problem is that the stock ECU goes into "closed loop".
Do some research on "closed loop", and you will find why messing with fuel injector sizes does not significantly affect closed-loop driving unless we're talking extreme changes in fuel injector sizing.

S-AFC won't do jack for fuel economy - see above on "closed loop".

How do you know it runs rich?
Do you have a wide-band on the car?
An FC *normally* gets around 15mpg with city type driving.

See other post about trying to attain 20mpg.


-Ted

Cybaster

i am aware of it eating spark plugs faster while using the CDI, but i thought that the spark is strong enough so that even though the spark plug gap is bigger, it still gives a strong spark so u can keep the plugs in longer =D

so doesn't that mean it makes spark plugs last "longer"?

WonkoTheSane

iTrader: (2)

Longer than the gap would normally be allowed to grow to? yes.

Longer than the spark plug would last without CDI? no.

The problem is that it's goign to reach that criticle wear spot a lot sooner, even though it's allowing more room than without the CDI..

You'll definately change plugs a lot more often with any form of ignition booster.

NZConvertible

In that case I would've thought you'd be a lot more careful this time around. Contemplating smaller injectors would suggest you didn't learn much from your experience.

This is a very clear indication that something is wrong with the car. You do not fix fuel consumption problems with mods, you find what's broken and fix it. This applies to any situation when the car is not running normally.

This just shows you don't have enough understanding of EFI (the Mazda system in particular) to start modifying it in such a random manner. The primary injectors are the only ones used below 3800rpm, and no matter how gently you drove the engine would always be running incredibly lean, causing terrible drivability (if it ran at all). Not only that, but there would be a huge stumble at 3800rpm when the amount of fuel being injected suddenly jumped up by 60%. And if you did put your foot down at low revs, you would almost certainly run dangerously lean before the secondaries kicked in, and probably end up with another dead motor.

No it wouldn't. You would actually be trying to trick the ECU into thinking nothing's wrong when something obviously is. This approach usually comes back and bites you in the ***. Like I said, find out why it's running rich and fix it.

If you want to average 20mpg you're driving the wrong car. The only way to do that would be to restrict its performance and drive like an old lady, which defeats the purpose of having a sports car. Stop trying to achieve something so pointless. Note that if you're doing short trips every day, average fuel consumption will always be worse than normal because the engine spends a greater percentage of its running time warming up, which requires richer mixtures.

Then you shouldn't post stuff like this:It's pretty clear from your age and admitted lack of knowledge ("I lacked understanding of the operation of fuel injection components", your words) that while you may have owned these cars, you had little to do with improving their performance. Posting info like this in an attempt to get us to respect you just pisses off the people who really do know what they're doing, hence the responses you received. The faintest whiff of BS tends to set people off around here...

This is a myth. In my experience the difference between a brand new O2 sensor and no sensor at all is ~5% tops. In normal driving (i.e. excluding long trips) it's only used for a very small percentage of the car's total driving time, and then it's only making relatively minor adjustments.