Crank Tuning

Holden/Delco Tuning. ALDL, OBD 1.5. Circa 1989 to 2004.
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Re: Crank Tuning

Postby Dylan » Tue Sep 15, 2020 9:24 pm

I don't remember the threshold off hand, but there's two stages of cranking fuel. Stage one is the initial then once that decay's either after time period or meeting an RPM threshold the code reads from the second table.
And from experience I'd scale the first stage as suggested by Vlad then reduce the second stage untill it starts successful.
Remembering that once the engine is above 400rpm it's deemed as running and then these tables aren't in affect.
So if it starts and stalls for example there's other tables to look at.

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Re: Crank Tuning

Postby h4x0r » Wed Sep 16, 2020 4:33 pm

Well... My current idea on how crank fueling works

When you first crank the car it gets the BPW from the "First Stage Crank Base Pulse Width vs Coolant Temp" table which is probably also adjusted by the "Injector Opening Time vs Battery Voltage" table. It then uses the Number of reference pulses before "initial crank fuel decay scaler" to subtract the "Crank decay step size (4 mSec for v8 factory). If it cranks pass "Number of ref pulses before secondary crank fuel" scalar then it moves onto the "Second stage crank base pulse width vs coolant temp" table. The the cycle repeats.

So I have managed to get the car to start when its hot!!!!


What I did is maxed out the number of reference pulses so it sticks on the First stage table just to get the bpw right. The battery voltage does drop while cranking so I lowered the bpw at lower voltages just incase that was causing it to over fuel.

I think the biggest difference was the fuel decay setting. Factory V8 is 4 mSec I was running 2 mSec and I lowered it to 0.5 mSec. Maybe I missed something in the newbie manual but I'm guessing my 60lb injectors should be 1/3 original which would be 1.33 mSec decay size.

The car is starting hot now. Hopefully I no longer need to pump the throttle open to get it to start.

Out of curiosity does anybody know how many pulses a 304 has per cycle? I assume its the amount of teeth for the dizzy hall effect sensor....?

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Re: Crank Tuning

Postby antus » Wed Sep 23, 2020 1:43 pm

Fuel decay is to do with timing. im a bit late to this thread, but what i'd normally do is calculate the percentage difference in size between the factory injectors and the new ones, and assuming the same fuel type and fuel pressure, change the stage 1 and 2 tables by that difference.

So if factory is 19lb (?) and the siemens are 60lb, 19/60=0.32, so then highlight all the cells in the stage 1 table and multiply the stock values by 0.32. Repeat for stage 2. In theory with everything else stock, that should be enough.

If your fuel pressure is 20% higher, take another 20% out of the timing.

Its only using this fueling to get the engine moving enough that the regular timing logic will work (above 450rpm) so its not using these tables for very long at all.

Having said all that Im not sure why you had to do what you did, but glad you got it working :thumbup:
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