Hi, what is the best way to tune for cold start. It is open loop, correct. Should I put it in speed density, and lean it out. That put it back to use the MAF.

 

Cold start usually lasts 215 seconds till the timer runs out, coolant hits something like 120* F and the O2's heat up and start switching. So you are not there that long and during that time the PCM is adding fuel to maintain a richer mix depending on the coolant temp. Also more inportant the air pump us running during the cold start so it pumping pure air into the exhaust manifold making it impossible to get a good AFR reading. AND until the o2's hit 600* F they are not accurate. Bottom line you really can't tune a cold engine because the sensors are not dependable and all the crazy things the PCM is doing to keep the engine running smooth and trying to meet the emissions requirements. .. Idle on a warm engine after hitting closed loop is totally different, at that time you can start tweaking things..

 

Forgot to ask.. Are you having problems, you can do some seat of the pants changes to Open Loop AFR Vs Temp table to lean it out . Idle RPM Vs Coolant Temp to speed it up or slow it down when cold. Prime pulse width if it cranks rich and needs throttle to kick over. Crank Spark Advance, etc These settings are usually not changed but may need tweaking with cam, injector and head mods. Key is you have to guess at the settings and then see if problem conditions get worse or better..

 

Wideband would help you out with tuning cold starts.