Mines set at 15.7, and so oscillates between 15.4 and 16.1ish on cruise

 

I don't think I got any better mileage, but it may be due to my setup. The AFR oscillations are pretty large in closed loop with my setup. If I move the sensor further up the DP, I think it will tighten up the swings and show some benefits. I'm also going to look for the algorithm in the ECU that controls the amplitude of the swings.

The leaner-than-stoich strategy is used in some newer cars.

 

figure you get less than 4 miles to the gallon at wot*. 4 vrs 25 or so cruising, you can see how much impact a wot means.

14.7 vrs 15, 16 or even 17 is a small percentage compared to the wot/cruise percent. So you have about a 1.x% supposed improvement in mileage by changing cruise afr. Low air pressure in a couple of tires would make a bigger difference.

* 5 miles to the gallon on a road course is typical, even if you figure half the time at wot and the rest of the time decelerating the real figure has got to be 2.5 and actual time at wot vrs the rest of the road course would indicate a wot mileage of less than 2 mpg.

It is neat seeing a leaner cruise, not sure why.

 

Your post isn't very clear..

I'm not sure if you are trying to say that its not a big deal because more fuel is used at WOT... I don't know about you but I spend about 99% of my drive-time off the racetrack idling or cruising... so a 6-10% (15.6 over 14.7) change in fueling there should be significant over time.

 

point was, one wot will kill any savings you might incur raising your afr.

but really it was an attempt to give a reason no one is seeing actual gas savings from making their afr leaner. Now, you might see a savings, but there have been a number of posts claiming the change did nothing, savings wise. To be fair most people are in the process of tuning their car so wot runs are part of the daily drive.

Nevertheless, I encourage people to do the mod. I just can't relate a reason. IOW I can't keep off the go pedal.

 

The main reason I cruise lean of stoich, and moderate throttle for that matter, is because it keeps the cyl head cooler, so when I do blast into WOT there is an initial thermal advantage in terms of margin of safety.

 

good, then there is a reason.
IT is news to me, I thought leaner was hotter. happy to hear what is really happening.?

 

Interesting article on fuel economy:

http://www.hondatuningmagazine.com/t...ing/index.html

First plot suggests 15.5:1 is optimum AFR for gasoline fuel economy even though it makes less power (higher manifold pressure required).

 

Any savings should still trend... I can tell you that I drive some full tanks of gas without stepping on it at all, mostly on the highway and sometimes get less fuel economy than times that I get on it 10-20 times through a few gears on that tank of gas.

...but yeah, as you said its still a good idea to save what you can... for both your wallet and the earth.

Yup... I don't remember the source but I thought we had previously established that 15.5 was the best for fuel econ.... but its good to remind everyone that less fuel is less combustible material.

 

Any updates with regard to the swinging AFR?

I found an article from the PLX wideband (http://www.plxdevices.com/AppNotes/PLXApp004.pdf) which says to increase closed loop targeting you can install noise filtering capacitors. They also show the wiring.

Supposedly that allows the ECU to see a common ground which increases the accuracy of the simulated narrowband signal read into the ECU.

I have no idea if it works or not but it seems that no one has mentioned this trick. PLX's wideband can't adjust the narrowband switchover, but their document was helpful non the less.

I'm about ready to purchase a ZT-3 plus ZR-1 gauge. Any reason to get the ZT2? I have no need for the extra features it seems.

 

The reason for a filtering cap is that this particular unit has a lot of noise on the output.

 

Both leaner and richer produce less heat. Near stoichiometric (14.5), the most heat is produced, so anything lean will use less fuel per output until it starts misfiring, which is about 15.3 (1.05 lambda) for gasoline, little leaner than 1.05 for alcohol.

The only reason for NB closed loop operation at stoich is to allow catalytic oxidation of carbon and nitrogen (CO to CO2, no to no2) with the cat, otherwise there is no reason to cruise at 14.7 - it wastes gas and heat soaks the engine.

 

any reports of this working on the 94170715 rom. I wish I could get this working.

 

One thing that's interesting is that a hot engine is more efficient than a cold engine.

Some truckers install big restrictive shielding over their huge radiators to cover half of it. When not towing they don't need all the cooling and it hurts economy, so by blocking the airflow the truck runs hotter and gets better highway mileage.

So knowing that stoich burn is the hottest, even though you save fuel by going leaner, you still have the loss of heat which can slightly hurt your mpg gains. I wonder what that trade off is and whether some method of increasing heat combined with a lean burn would help even more?

 

For spark ignition engines, 15.0 - 15.6 to 1 air to fuel is where peak efficiency is. Compression ignition and spark ignition are completely different fruits