Why cold start?

[gpvecchi]

I think cold start help raising fast the first catalyzer temperature, in order to reduce pollution, right?
Wouldn't it reduce its life, as it's pushing unburnt fuel inside the catalyzer?
In this wouldn't it better to tune it out?
And, it's useless with uncatted headers, right?

[mav1178]

unburnt fuel inside the catalytic converter isn't the issue, it is excessive temps beyond 1700F that only happens when the car runs excessively rich after operating temperatures are reached. so when the catalytic converter is cold, it doesn't matter.

beyond 1700F you start to melt/destroy the honeycomb and metals inside the cat.

high idle cold start isn't needed for cars without a cat.

[gpvecchi]

Thanks! And for cars with just the cat in the front pipe?

[tomm.brz]

Cold start is hard coded, you can t tune it out
only reduce rpm and anticipate timing if you want, still the ecu will split the injection and make a late stratified injection directly into exhaust stroke

you don t need torque to be produced i nthe very beginning of engine starting, so just keep timing a bit retarded to help the lambda and whole exhaust warm up easier

[Westen86]

Originally Posted by tomm.brz

Cold start is hard coded, you can t tune it out
only reduce rpm and anticipate timing if you want, still the ecu will split the injection and make a late stratified injection directly into exhaust stroke

you don t need torque to be produced i nthe very beginning of engine starting, so just keep timing a bit retarded to help the lambda and whole exhaust warm up easier

This is not entirely true. My OFT tune has the cold start tuned out. There is no bark when it first cranks over, just a normal smooth idle. Like if I was starting it warm. I have catless header, stock FP.

[Tcoat]

Originally Posted by mav1178

high idle cold start isn't needed for cars without a cat.

The high idle, rich mixture, cold start process has existed since about the Model A. It just used to be done with a choke instead of a computer. Cold start high idle is about more than just heating up the cats. It is also about building oil pressure and reaching proper operating temperature more efficiently.

[RToyo86]

Originally Posted by Westen86

This is not entirely true. My OFT tune has the cold start tuned out. There is no bark when it first cranks over, just a normal smooth idle. Like if I was starting it warm. I have catless header, stock FP.

That's just idle speed and timing adjustments as Tomm mentioned. It's still coded in just not OEM specs. After a certain amount of time you will see the idle speed and timing change.

Standard RPM is around 1500 and timing is around 11° retarded. OFT adjust idle speed around 1100 and timing closer to 0°

[mav1178]

Originally Posted by Tcoat

The high idle, rich mixture, cold start process has existed since about the Model A. It just used to be done with a choke instead of a computer. Cold start high idle is about more than just heating up the cats. It is also about building oil pressure and reaching proper operating temperature more efficiently.

I forgot about the choke, I took a motorcycle class once and they had us use this to start the bike.

people also forget that high idle used to be via coolant temp sensor/ECU control + IACV which usually had a bimetal element that caused intake air to be bypassed, thus resulting in a cold start high idle. modern engines don't have quite the same system anymore.

and yes, warming up the engine was critical. not everyone has the luxury of slowly driving your car to reach operating temps ...

[mav1178]

Originally Posted by gpvecchi

Thanks! And for cars with just the cat in the front pipe?

see my first post, nothing changes with 1 or with 50 cats other than stupidity of design

[tomm.brz]

Originally Posted by Westen86

This is not entirely true. My OFT tune has the cold start tuned out. There is no bark when it first cranks over, just a normal smooth idle. Like if I was starting it warm. I have catless header, stock FP.

As I said, the cold start is hard coded and you can t tune it out


you can tame it down, as yours is right now


During cold start injection is stratified with early Port injection at 50%, and the other 50% is late injected by direct injection basically directly into exhaust


Tameing it down as you did just reduce the bark, and produce more torque into the crankshaft and less heat is diverted into exhaust


nonetheless, just do what you like, not so important anyway, I keep normally -3 of advance timing during cold start, and rpm under 1200

[tomm.brz]

Originally Posted by RToyo86

That's just idle speed and timing adjustments as Tomm mentioned. It's still coded in just not OEM specs. After a certain amount of time you will see the idle speed and timing change.

Standard RPM is around 1500 and timing is around 11° retarded. OFT adjust idle speed around 1100 and timing closer to 0°

Late models have actually around -19/-20 of advance timing, that's the software reachable limit for the ecu
Probably to get faster hot temp in exhaust when you crank on the car
Exhaust temp climbs really fast from ambient to more than 600 Celsius in like half a minute

[tomm.brz]

Originally Posted by Tcoat

The high idle, rich mixture, cold start process has existed since about the Model A. It just used to be done with a choke instead of a computer. Cold start high idle is about more than just heating up the cats. It is also about building oil pressure and reaching proper operating temperature more efficiently.

Yes


and the engine warms up faster by the friction of the pistons other than the combustion itself
High rpm help in this regard


I see people all the time trying to warm up the car letting it idle for many minutes and then lugging the engine changing gear under 2000rpm and then they use too much throttle to move because there is no torque there


My warm up is always: move right away, and change gear at at least 3000-3200 rpm with very light throttle

[Compelica]

Slightly related - is there a learning component for the ECU when starting the engine? Starting the engine after the first flash always requires more cranks as compared to a car driven for a while.

[tomm.brz]

Originally Posted by Compelica

Slightly related - is there a learning component for the ECU when starting the engine? Starting the engine after the first flash always requires more cranks as compared to a car driven for a while.

That s not always true
cold start is a open loop moment, so it depends on how the tune is set
Also, after a reflash, vvt is always off, compared to after a while, when vvt is most of the time already on almost immediately


but, yes. there is some kind of fuel trim that is learnt and then set also during cold start