How to run leaner then 14.7 on e85

[Foose04]

Hey guys, is there any way to run leaner then 14.7 in closed loop to aid in fuel mileage? Mine actually seems to run more around 14.2-14.4 and I know it's hurting mileage. This is on a 2004 gmc with SD tune.

Thanks!

[Throttle]

e85 is 9.7 not 14.7

[Foose04]

Yeah same page on that. If I input a higher stoich will it run leaner during close loop?

[wyochimneysweep]

no the trims will put it back to stoich. you can try changing the o2 switch points

[LSxpwrdZ]

the stock o2's don't know AFR. All it knows is lambda 1.0. Your wideband may read 14.7 on e85 but that is just because your wideband is reporting lambda 1.0 as 14.7 when actually it's more like 9.7:1 afr. Do yourself a favor and learn Lambda! Makes things much much easier.

Now on to your tune, as long as you have your stoich value correct to your fuel type and the tune dialed in you can play with the switchpoints of various airflow modes to obtain a desired wideband reading. Switchpoints are in mV and the higher the mV reading the richer it is, so to lean it out you would want to lower those numbers.

You can run in open loop with your wideband and adjust the tune to where you want it to stay at and log just the o2 mV readings to see where they stay at at the afr your wanting to achieve.

[RWTD]

I have never seen E85 run more efficient when you have it running leaner than its true stoich point.