Cold Cranking Tables
Posted: Wed Oct 13, 2010 2:11 pm
Hey guys,
Spent a lot of time playing on the bench with an S13 KA24DE (53F10) ECU last night to try and get some answers for cranking enrichement. Some guys have had trouble with engines flooding on startup when using large (740cc+) injectors.
I set it up for Coolant temp = 26 degrees (as low as my bench setup currently goes), TPS = closed, AFM = 1.1V, RPM = 500 and Start = ON. I noticed that the injector pulsewidth sounded like it was changing even though the Consult reported pulsewidth remained constant. So I hooked up the CRO and monitored the actual pulsewidth. Sure enough it was changing.
The table to change for cranking is correct in NIStune - “Crank Enrich”. The confusing part is that the cranking inj pulsewidth is NOT reported by consult. AND the KA24 ECU goes to "batch fire" mode while cranking! It truly is a percentage based table. If you put 255's in there the injectors will open 100% of the time. That's right - like putting a 12V battery across them! A value of 0 gave 1ms (which must somehow be limited to 1ms instead of actually going to 0 – even with TTPmin at 0). A value of only 10 gave 10ms. That’s quite a lot of fuel if you have 740cc injectors!
Other points of note – After you’ve been cranking for a few seconds (Start signal = 12V) the ECU will start pulling the pulsewidth back. Presumably to avoid totally flooding the engine if a user is silly enough to just keep cranking when the engine doesn’t start. Other thing is after starting (Start signal = 0V) the ECU interpolates between the cranking pulsewidth and the normal idle pulsewidth – presumably so there’s a smooth transition from starting to idling.
So, bottom line is to multiply the values in that table by your injector ratio old vs new – as NIStune does automatically now. So if you've got 740's and std were 270's (are KA's 270 or 370??) then you'd divide all values by 2.7.
I’m yet to try other ECU’s. But I'd expect ECU's from the same family (S13, U13, RNN14 SR20DET) to behave the same.
PL
Spent a lot of time playing on the bench with an S13 KA24DE (53F10) ECU last night to try and get some answers for cranking enrichement. Some guys have had trouble with engines flooding on startup when using large (740cc+) injectors.
I set it up for Coolant temp = 26 degrees (as low as my bench setup currently goes), TPS = closed, AFM = 1.1V, RPM = 500 and Start = ON. I noticed that the injector pulsewidth sounded like it was changing even though the Consult reported pulsewidth remained constant. So I hooked up the CRO and monitored the actual pulsewidth. Sure enough it was changing.
The table to change for cranking is correct in NIStune - “Crank Enrich”. The confusing part is that the cranking inj pulsewidth is NOT reported by consult. AND the KA24 ECU goes to "batch fire" mode while cranking! It truly is a percentage based table. If you put 255's in there the injectors will open 100% of the time. That's right - like putting a 12V battery across them! A value of 0 gave 1ms (which must somehow be limited to 1ms instead of actually going to 0 – even with TTPmin at 0). A value of only 10 gave 10ms. That’s quite a lot of fuel if you have 740cc injectors!
Other points of note – After you’ve been cranking for a few seconds (Start signal = 12V) the ECU will start pulling the pulsewidth back. Presumably to avoid totally flooding the engine if a user is silly enough to just keep cranking when the engine doesn’t start. Other thing is after starting (Start signal = 0V) the ECU interpolates between the cranking pulsewidth and the normal idle pulsewidth – presumably so there’s a smooth transition from starting to idling.
So, bottom line is to multiply the values in that table by your injector ratio old vs new – as NIStune does automatically now. So if you've got 740's and std were 270's (are KA's 270 or 370??) then you'd divide all values by 2.7.
I’m yet to try other ECU’s. But I'd expect ECU's from the same family (S13, U13, RNN14 SR20DET) to behave the same.
PL
