Adjusting Stoich on tune

[Fastmax32168]

Got it. Best explanation I have seen. Thanks

[Turnshredder]

14.7 is only for closed loop. I have tried to adjust mine to say 15.5 or 15 to 1, for better fuel economy, and it didn't seem to do anything. I did this under scalars/open loop afr parameters/stoichiometric afr. ??

[steveo]

most fuels do not burn at 14.7:1 anymore. no matter what you do to 'change the stoich ratio' in your ecm, when in closed loop your narrowband o2 sensors will try to get to half a volt or whatever is configured, which is stoich of whatever fuel you're burning. o2 sensors can't target a ratio, only stoich.

the only reason you would change the 'stoich' parameter in your ECM is so it doesn't have to trim as much to get there, the ecm does not have the ability to maintaining that ratio in closed loop.

if you want to try to burn a bit leaner than stoich, you can try to tune the o2 voltage that closed loop tries to get to. you might be able to tune it to 420-450mv without losing stability which ends up being very slightly leaner.

lets say you want to run 15:1 on gasoline that burns at 14.7:1 stoich so you adjust your o2 voltage

15:1 with regular gasoline usually ends up being like 200mv on the o2 sensor

that's fine but on a lot of o2 sensors, 17:1 is like 150mv and 20:1 is around 100mv

so what ends up happening is it just flutters back and forth from lean to barely running at all and runs like crap

the only real way to run leaner than stoich is open loop or get some kind of closed loop with a wideband rig of some kind