The stock ecu will run closed loop on most crusing and idle conditions

In this mode the ecu adjusts the long term and short term fuel trims based upon the feed back of the front 02 sesnor to achieve a ideal a/f ratio of 14.7 at all times

When the car transitions to more load the car will switch to open loop operation where there is no feed back loop

A tuner will adjust the cross over point and open loop operation mode. Also the car will be trimed to minimize any corrections in closed loop mode to get the car close to a 0 (zero) correction.

However, the ideal a/f ratio target is not generally modfied as this is a law of physics not a tuneable parameter. It is possible to adjust the actual desired a/f target on closed loop the ecu looks for in many reflash programs, however, this is not generally something I adjust.

I hope this makes sense - if not feel free to follow up.

 

Noize, While it is true, weight and high rev at highway cruizing all adds to low mileage but I also think the OEM injector size (660 cc/min) are a very significant cause for the gas consumption in the X. The OEM 4G63 (eclipse/talon/laserGen1) was rated at 195hp and I got ~27-28 mpg on highway. The X is rated at 295 hp. So how did the X achieve the 100hp? Answer: bigger injectors (440cc/min in 4G63), more aggresive cams and bigger turbo, etc. The Gen1 elipses' were lighter but I think that the weight was less of a factor than lower performance parts.

Later, Ken

 

Honestly the X doesn't get that horrible of gas mileage. Go look at the new v6 auto accord. It gets a whopping 18/26 mpg. Thats like 2 mpg better than the X.

 

Let me help you out. The best gas mileage is achieved around 15.2-15.4:1 AFR. Unfortunately when you cruise the AFR is at 14.7:1. Why? Emissions. 14.7:1 gives the least emissions and keeps the Cat happy. 15.2-15.4:1 will destroy the cat in no time.

So the first step, if you want to run 15.2-15.4:1, is to get rid of the stock cat. You replace it with a test pipe.

The second step is to get yourself a wideband that simulates a narrowband sensor and get it installed. Then you disconnect the wire that sends the signal from the ECU to the stock O2 sensor. That signal keeps the car running at 14.7:1 in cruise and idle. Keep the heater O2 sensor signal connected so you will not get a CEL.

The third step is to take a wire from the analog out of your wideband and connect/tap into the wire that goes straight into the O2 sensor.

Finally, you can program your wideband to send a signal to the stock O2 sensor to allow the car to run at 15.2-15.4:1 at idle or cruise.

You are basically by-passing the stock O2 sensor and allowing your wideband to simulate a narrowband O2 sensor. Your are tricking the ECU into allowing your car to run at 15.2-15.4:1

This process should net you an improved mileage of about 2-3 mpg.

This is the most common way used to tune for mpg at cruise and idle.

Some have tried tuning the cruise/idle fuel map for better mpg, but the results have been mixed.

I have tried both ways and found the former to be more consistent.

 

Ken,

I can't agree with you. First of all, injector size has nothing to do with fuel economy if a car is mapped properly. My Evo VIII got the best fuel economy when it had 680cc injectors and a big turbo. Bigger injectors have greater flow potential when needed, but don't get worse fuel economy on the highway cruising.

Second, check this out: http://www.turbomagazine.com/tech/08..._manifold.html They claim that they pulled the engine and found that it uses 540cc injectors. This would help support why I am seeing nearly 90% IDCs at very high RPM. But injector size doesn't really have anything to do with the final point below.

The 1G Eclipse and 2G Eclipse had an even taller fifth gear than the Evo VIII which is taller than the IX, and the X has the same 5th as the IX with a shorter final drive. The gearing and lack of weight are why the older cars get the best fuel economy.

 

REPEAT AFTER ME: THE ONLY REASON OEM'S TARGET A CYCLING AFR AROUND STOICH IS FOR PROPER OPERATION OF THE CATALYTIC CONVERTER!
The converter stores oxygen while lean, then uses it when rich, in a cycle.


There is NO other reason for it.

There were, and are, special lean burn vehicles that used special converters that stoich means squat.

Where do y'all think wideband sensors came from? LEAN BURN VEHICLES!

 

The cat and warranty is also probably one of the main reasons its fueled so rich in open loop.

I can't really disagree with someone like you or Naji going half a point leaner than stoich at cruise. I do think 16.8 as mentioned earlier in the thread is very excessive.

Lots of people in my area run cats due to the type of emissions tests we have and the ramifications if you were to get caught without one. Others just care about the environment and don't want to run a test pipe.

 

16.8 is not excessive. I believe a new Honda engine runs at 22:1 during cruise. I ran 17.5 on my Evo 8 during cruise with no problems. During cruise there is very little load, so a lean mixture has no ill effects.

Check this out. Scroll down some for info on the Honda engines.
http://en.wikipedia.org/wiki/Lean_burn

 

Are you running your Evo that lean at cruise with a cat?

Coming clean, I fried a catalyst on an NA Mazda RX-8 Renesis engine. Those cars get just horrible fuel ecomomy. Granted, they have hotter EGTs than piston engines, but they don't take too kindly to being leaned out much, even a little at cruise. It didn't happen right away, but I believe the custom tune contributed to it over time.

I'm not set leaner than stoich in my X. I have hypermiled it and sustained 27.5mpg on the interstate. I can also drive like a head case and see 19mpg on the interstate.

 

Running lean for just the heck of it is pointless. From my reading, there is no point running beyond 15.5:1 to save gas. Did you test if running 16.8:1 gave you better gas mileage than running 15.5:1?

 

Carbureted Japanese cars were running much leaner than that in the late 70's/early 80's.

CVCC anybody?

Stratified charge?

They got away with it because they didn't need a catalyst to meet 48 state emissions.

Wake up people, its all been done before.

 

Grocmax,

Man I haven't spoken too you in years, good to see ya!

What does everyone think is the safest lean cruise to run with the cat? would 15.7:1 be acceptable and possibly gain 1-2mpg?

 

Noize, Ok I stand corrected; the injectors in the X are not 660 but 540. That said, they are larger than those in the OEM 4G63. I am a little confused about your results, however, namely larger injectors and turbo gave better mileage. I thought a smaller injector would meter out fuel more efficiently than a larger one under low load conditions vis., cruizing.
Additionally, if raising A/F ratio using a CAT increases mileage by 1-2 mpg (as per above posts), it does not seem worth the effort. So going down your road of either reducing vehicle weight and lowering engine rpm in 5th gear, I wonder how much one would have to lose in weight and what reductrion in gear ratio would be needed to get a significant increase in mileage, say at least 5 mpg? Your thoughts? What is interesting is we probably wouldn't even have these discussions/considerations if gas was <$3/gal or we were all very rich!!

Later, Ken