Lean AFR during cold start

[tomm.brz]

Curious about what you guys get as AFR during start with cold engine
tuned many cars remotely and locally and always see around 15.44 target afr during cold start.. then slowly going to stoich as it warms up
Still haven't figured out how to hijack this leaning as it seems to me hard coded into ecu and/or not defined in ecutek tunes


Why do these cars lean out during start? I thought OEMs usually made the cold start rich to provide a more stable idle

[steve99]

O2 sensors dont work accuratly till they are warmed up to a few hundred degrees


Check fuel system status is not 1 warmup mode.

[tomm.brz]

it persist a bit also after the fuel system status 1
it starts 15.44 then 14.99, then 14.90 then 14.7 after a while
also I have a aem wideband that pre heat itself, and actually even when cold, the stock lambda seems pretty good when not warmed up totally

Also even if fuel system status is "1".. why do this car target a leaner afr during this status and during cold start, when logically should be rich?

Anyway looking at Catalyst#1 temp, i think the sensor go in temperature pretty soon since i reach 600 celsius in less than 30 seconds, after 5 seconds is already at 200 celsius

[nikitopo]

Originally Posted by tomm.brz

Anyway looking at Catalyst#1 temp, i think the sensor go in temperature pretty soon since i reach 600 celsius in less than 30 seconds, after 5 seconds is already at 200 celsius

I guess you mean 100 celsis in the first 30 seconds. I was thinking maybe they do this to warm up the catalyst sooner?

[tomm.brz]

Originally Posted by nikitopo

I guess you mean 100 celsis in the first 30 seconds. I was thinking maybe they do this to warm up the catalyst sooner?

In the cold start, even with lower idle and less retard than a stock tune, it heats up so much quicker than you think.. try log catalyst#1 temp

[steve99]

Originally Posted by tomm.brz

it persist a bit also after the fuel system status 1
it starts 15.44 then 14.99, then 14.90 then 14.7 after a while
also I have a aem wideband that pre heat itself, and actually even when cold, the stock lambda seems pretty good when not warmed up totally

Also even if fuel system status is "1".. why do this car target a leaner afr during this status and during cold start, when logically should be rich?

Anyway looking at Catalyst#1 temp, i think the sensor go in temperature pretty soon since i reach 600 celsius in less than 30 seconds, after 5 seconds is already at 200 celsius

Yeah its not going to provide accurate reading till its arround 600 plus celcius


And theirs a lot of offsets applied during cold start phase. Probably many not known or not defined in tables

[tomm.brz]

i do see the fuel quantity total going down while it warms up, but the wideband says it's lean.. is it really for cat warming up faster?

[steve99]

Originally Posted by tomm.brz

i do see the fuel quantity total going down while it warms up, but the wideband says it's lean.. is it really for cat warming up faster?

Believe so, retarded timing and lean afr will create heat.