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Author Topic: FKSTT with bigger injectors  (Read 334 times)
nupustas
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« on: January 12, 2022, 11:56:32 AM »

Hi,
1,8t engine, ME7.5 ecu. Running on A98 petrol with zero ethanol. In the summer i installed bigger injectors (bosch EV14 731cc, 0280158235). KRKTE 0,0445, TVUB cannot find for these injectors, so using tvub from 750cc ev14 (1.9202   1.3308 1.0295 0.7708   0.6908 ). Car runs good, fuel trims in few percents, but now weather bacame colder (0°C...-10°C), and i need to crank about 2...3 seconds till engine starts. When it starts-everything ok, no pulsation or smth, car runs like from factory while warming (i have to lower KFFWL maps a little bit). Earlier i was installed 440cc, 550cc injectors, but doesnt have any problems with cold start. So questions:
1. Do i need to adjust FKSTT maps, if i'm stay at A98 petrol? From that i understand, i shouldn't touch it's, because these maps are just phisics - how many fuel evaporates at temperature levels?
2. Maybe different injector angle or big port head can affect it? For example, more fuel stays on wall?
3. While cranking cold engine, voltage about 10V, so maybe in this area TVUB is realy wrong and can causes problems with cold start?
4. From atached log i see, that injection time drops while cranking till engine starts, this is normal?

Maybe someone have any ideas?
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nupustas
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« Reply #1 on: January 14, 2022, 11:01:19 AM »

After reading FR, i found that not only FKSTT is for cold start - also important KFWKSTT (0, 1). Looks like i should leave TVUB alone
From my log i guess, that i'm flooding engine, and it starts only when injection time drops (lets say "cylinders are ventilated from overfuel". Maybe cold start factor with bigger injectors bacame too big in cold weather? So what i done:
1. Set TVUB to stock (for 750cc injectors)
2. Set FKSTT to stock
3.Lowered KFWKSTT table 20perc

And car stars easily. But there is some question. I'm on the right way, tweaking right maps? If yes, how to properly calculate KFWKSTT? It correction factor for every revolution of engine during start - i have no idea how to look into cylinder and see that it's happening(overfueling or lean)
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