95 lt1 injector offset questions

[Fast355]

Just a quick question along those lines steveo - do you know, is the pulsewidth reported in the $EE datastream before of after this adder?

Your point is valid however - the operating range we're talking about here is going to be very rarely encountered for reasonably sized injectors.



No, you'd need to skew the entire offset table. The slope of the injector is assumed by the fueling equations to be a linear constant (even though it rarely is).

Edit: also, it's not a flow rate modifier. It's correcting delivered fuel mass for a region of the injectors flow curve that doesn't match the injector flow constant slope.

Though I'm scarcely qualified to teach a remedial course in fuel injection flow characterization, if I get bored enough I'll try to draw up a couple graphs to illustrate the difference between older type 1 / 2 knees and what a type 3 injector looks like. The graphs Fast355 referenced on injectordynamics are of type 3 injectors.

The topic I'm more interested in is how would you advise yoheer to proceed given the injector characterization posted here?

ACCEL 150136 - 36# Hr Fuel Injector Specifications
Drive Circuit: "Saturated", R-C Voltage Suppression, 14.0 VDC
Coil Resistance: 14.5 ohms
Fuel Compatibility: Standard Gasolines and Ethanol Flex Fuels
Fuel Pressure: 300 kPa (43.5 psi)
Static Flow Rate: 252 gm/min n-Heptane
Dynamic Flow Rate: 7.56 mg/pulse at 2.5 ms, 10 ms period (100 Hz)
Approximated Time Offset: 0.70 ms
Approximated Slope: 4.20 mg/ms
Minimum Linear PW: 1.38 ms
Linear Flow Range (SAE): 15.3
Opening Time: 1.35 ms
Closing Time: 0.67 ms
SMOV: 4.23 volts

The point you are missing is that the angle of the knee does not matter. It still going to deliver less than the theoretical delivery base off pulsewidth thus the numbers will still need to be a positive number. The injector that has more initial delivery will just have lower values in the adder table. The injector that has less flow initially will have larger numbers. Either way you still have to add to the total pulse width to get the full fuel charge.

I spent some time messing around getting the injector data correct on the 42# Ford 6.2L "Raptor" injectors in my P59 run 383 with a L31 Marine intake. Using the data in the Ford Raptor PCM, at a differential pressure of 58 psi, the break point corresponds to 1.667 msec. Over 1.6 msec the injector flow is characterized by the high slope values, under 1.6 msec it is the low slope. The low slope value has a higher flow rate, but the values are 0.121% different. I used an exponential curve to mathematically approximate the difference. At 0.06 msec commanded pulse width the injector in theory needs 0.2 msec more to get that 0.06 msec desired flow amount from that point on the difference reduces until it disappears into a number the P59 will not even save at 1.64 msec. In the grand scheme of things that is almost nothing. My idle pulse width is ~3.5 msec at hot idle. During deceleration the pulse width drops to 2.2 msec. I would need roughly double the injector size before the short pulse adder really came into play. As said before this would make a difference on an engine with really large injectors like a turbo build, but with reasonably sized injectors its not something that would ever come into play. Even with double the injector size, it would still likely idle above 1.6 msec and any issue in deceleration could be compensated for by activating DFCO for a brief period. Ford did exactly that on the mid 90s Cobras with the 351 to get them past emissions and smooth out surging that might otherwise exist from inconsistent fueling during deceleration.