Injector current trace shows slower opening when hot
07-31-2012, 12:33 AM
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Injector current trace shows slower opening when hot
These are both taken with Vbatt = 14.4 V
COLD (30°C)
HOT (restart 5 min after coolant at 99°C)
These are with hi impedance 600cc injectors.
There is at least a 100 us difference in dead time cold vs. hot.
This 100 us represents a 15% change in fueling at idle.
The reason for the above is that copper's resistance goes up with temperature. I saw a shift from 15-19 Ω.
With a higher resistance, it takes longer for the current to build and reach the point where it can begin to move the pintle.
What's worse is that if actual dead-time at hot is set too short, when the ECU calculates a narrower pulse (like if O2 feedback is swinging back down), it will lean out way more rapidly than intended and can cause stalling.
This explains why if I set my dead-times for warmed up conditions, when cold O2 feedback goes tto -15 to -20%.
If I set my dead-times for cold, it tends lean misfires at low MAP, and stalls abruptly when O2 correction swings negative. AFR will go slowly leaner, than abruptly go very lean.
I have an idea for a circuit to address this problem, but it would be neater if Reverant put it into his new enhanced board.
COLD (30°C)
HOT (restart 5 min after coolant at 99°C)
These are with hi impedance 600cc injectors.
There is at least a 100 us difference in dead time cold vs. hot.
This 100 us represents a 15% change in fueling at idle.
The reason for the above is that copper's resistance goes up with temperature. I saw a shift from 15-19 Ω.
With a higher resistance, it takes longer for the current to build and reach the point where it can begin to move the pintle.
What's worse is that if actual dead-time at hot is set too short, when the ECU calculates a narrower pulse (like if O2 feedback is swinging back down), it will lean out way more rapidly than intended and can cause stalling.
This explains why if I set my dead-times for warmed up conditions, when cold O2 feedback goes tto -15 to -20%.
If I set my dead-times for cold, it tends lean misfires at low MAP, and stalls abruptly when O2 correction swings negative. AFR will go slowly leaner, than abruptly go very lean.
I have an idea for a circuit to address this problem, but it would be neater if Reverant put it into his new enhanced board.
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