RomRaider

I can't change AFR's to 15.0 on the low det or high det tables. If I do it using ECUFLASH it will show AFR's of 4.99 instead of 15.0. I dont know if is safe.

Change your Closed Loop Target A/F to 15:1 if you want to conserve gas.
Then just leave the 14.7 in your maps alone. I have tried this and it works, but didn't save any gas really lol.

thats because of a misconception about what the fuel tables actually represent.

they don't represent AFR, they really represent how much injector pulsewidth to add to stoich at a certain load point, its just displayed as AFR for some reason.

So, it wont go lower than stoch?

Tuning with UTEC I got 15.5-16afrs. 28mpg @ 85mph for 75miles. Thats on a stg4 WRX

If this is true, doesnt that make MAF scaling to hit correct AFR during open loop based on the fuel map more or less invalid since an increase or decrease in pulsewidth cannot exactly translate to an AFR reading, especially with other than stock ignition timing and boost???

BTW, for anyone running cats in their system, it's a bad idea to run leaner than 14.7 as it will cause your cats to self destruct in a short amount of time.

But FWIW, when I was testing it, for some reason the only time going leaner worked for me was at idle. When moving, it seemed to run at stoich no matter what (had closed loop AFR set to 15.0:1).

ok, change stoich in my post to "what subaru/denso defined as stoich or base pulsewidth"

then it applies.

if you change what the airflow versus base fuel flow is, of course your AFRs are gonna be off.

like if I set my injector scalar to 125% of what it should be, its gonna run an equivalent amount leaner, until LTFTs bring it back into line.

2006+ models do not have this "Closed Loop AFR" setting found yet. The car runs between 14.2 and 14.6 during cruise. It could use some leaning.

If you are running leaner or richer than 14.7, then your EGT's are going to go down. Stoich for gas (14.7) is where you are going to see the hottest EGT's. Thats why they use it for emissions,it has the most complete burn, and the cat is hot enough to help reduce emmissions. You aren't going to do anything to the cat by running leaner -- only cool it off

I am sure that jfitzpat has a chart that can help explain.

A graph to help explain:


I was looking for an EGT vs Stoich chart but I havent found it yet.

Lower EGTs doesn't have anything to do with being being lean causing cats to overheat and self destruct. It has to do with the ratio of oxygen to hydrocarbons left over in the fuel.

The surplus oxygen in the cat is what causes the cat to overheat, even if EGTs go down.

To quote the Catalytic converter article from wikipedia:


You will notice the ECU running richer than stoich in closed loop after the the has run lean for a bit, for example after coasting in gear. That's the ECU dumping extra fuel into the system to cool down the cat.

I could very well be wrong, but according to this document http://www.autoshop101.com/forms/h64.pdf all your going to do by running leaner is fail emmisions. It does not say anything about running lean and destroying the converter.

It does however, state that running overly rich will cause the converter to overheat and "melt down" due to unburnt fuel being consumed by the converter.

Edit:
Here is another site http://www.fulllineexhaust.com/products/converterfailures.asp that is easier to read. Snippit from site listed above:

It's better to think of those tables as enrichment tables and each entry, after scaling, represents a percentage enrichment relative to stoichiometric. Negative values (i.e. enleanment) aren't supported.