06-16-2022, 03:52 PM | #1 |
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Why cold start?
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? |
06-16-2022, 05:34 PM | #2 |
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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. |
06-17-2022, 03:07 AM | #3 |
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Thanks! And for cars with just the cat in the front pipe?
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06-17-2022, 05:35 AM | #4 |
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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 |
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06-17-2022, 10:51 AM | #5 | |
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06-17-2022, 10:52 AM | #6 |
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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.
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06-17-2022, 11:48 AM | #7 | |
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Standard RPM is around 1500 and timing is around 11° retarded. OFT adjust idle speed around 1100 and timing closer to 0° |
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06-17-2022, 01:34 PM | #8 | |
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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 ... |
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06-17-2022, 01:35 PM | #9 |
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06-18-2022, 07:00 AM | #10 | |
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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 |
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06-18-2022, 07:03 AM | #11 | |
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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 |
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06-18-2022, 07:07 AM | #12 | |
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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 |
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07-09-2022, 12:08 PM | #13 |
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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.
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07-11-2022, 01:01 PM | #14 | |
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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 |
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