Single Fire/Double Fire

[festy]

Sorry to hijack, it looks like in the v112 blcf v8 stock bin the double fire option is natively set?

Does that mean it will run twice the set injector rate for crank/run if left unset?

Double fire Injects the fuel in two halves, single fire injects it all at once - but same amount all up. Because single fire only uses one of the two injection opportunities, the injectors are effectively limited to half their duty cycle.
...or at least that's my understanding of how it works.

With massive injectors and tiny BPWs at idle, it's hard to get the fuelling right in double fire because it halves the already small pulse width, and 2x dead time offsets etc.

[VX L67 Getrag]

Ahh cool that makes sense!!!

If it were a MAJOR code change it would have warning & implications but as it was a standard CODE change I didn't think it would be of significance, I will try my other settings & see how it goes!

[v6bucket]

Thanks Festy.
Dylan, injectors are Siemans Dekar 60lb.
VX L67 Getrag, don't worry about the hijack, as long as someone learns something.

[blownvp]

been experimenting with bigger injectors set up single fire below 2ms tuned the ve with a wideband then changed back to double fire and the afrs changed slightly on wideband between single and double fire running open loop so no correction.think its how the injectors flow at the lower pulsewidths in the non-linear area.another way is you could alter the injector deadband or offsets to bring it back in line.also sometimes you can feel the changeover point.running e85 now with deka 60 so i can get away leaving it double fire this is early batch 808.

[VL400]

LOL thanks Dylan, the way it started was trying to use your tune as a base for the other mentioned I another thread with a 106* lobe seperation & caused a immediate flood?

So I thought could be a coding error with single/double fire option!

No just tune related There is no issue with the single/double fire auto switching and will be helpful once you install larger injectors, its not needed with blue tops so leave it in double fire mode.

Double fire Injects the fuel in two halves, single fire injects it all at once - but same amount all up. Because single fire only uses one of the two injection opportunities, the injectors are effectively limited to half their duty cycle.
...or at least that's my understanding of how it works.

With massive injectors and tiny BPWs at idle, it's hard to get the fuelling right in double fire because it halves the already small pulse width, and 2x dead time offsets etc.

That is correct Its also a trap as logging will show > 50% duty cycle, but the hardware wont be delivering it (this is '808/'3082 etc only, later PCMs no such issue).

been experimenting with bigger injectors set up single fire below 2ms tuned the ve with a wideband then changed back to double fire and the afrs changed slightly on wideband between single and double fire running open loop so no correction.think its how the injectors flow at the lower pulsewidths in the non-linear area.another way is you could alter the injector deadband or offsets to bring it back in line.also sometimes you can feel the changeover point.running e85 now with deka 60 so i can get away leaving it double fire this is early batch 808.

With deka 60s and E85 you should have no difference between single and double fire and wont need to muck with the VE once the opening table is setup to match the injectors.

[antus]

Yep, single fire would only be used at low pulsewidths (as defined in the tune) so it wont cause you to run out of fuel at high load. If you have a stable idle and adjust the single/double fire thresholds so the mode changes at the delivered idle pulsewidth, you should see no changes in fuelling on the wideband. If you do then your injector dead time vs voltage settings are not accurate. You can use differences measured like this to fine tune the dead time settings @ your running voltage too. VL400 has the maths to calculate from the difference which I cant recall, but essentially you can toggle single/double and adjust dead time at running voltage untill the measured AFRs on the wideband dont change as you toggle. Then smooth your changes in to the nearby voltages. We use this on a nissan 300zx with unknown jap injectors where the car never gets over 20% duty cycle even at WOT full boost to give a stable idle where the injectors are struggling at idle to give stable fuel delivery at tiny pulse widths.

[v6bucket]

I'm probably getting out of my comfort zone here, what is "Injector Dead Time" listed in 12P? Can you give me an example?

[Dylan]

Dead time is how long the injector takes to open. There is a table with different voltages.
Not sure of the name it's "injector voltage offset" or similair. Its between spark tables and ve tables on the xdf.
And below it is the ms add on times. It's fairly important to have these pretty right.

[immortality]

Basically put it's the time between when voltage is applied to the injector and the time it actually starts to open and flow fuel.

[v6bucket]

Dylan, "Injector- Injector Bias vs Battery Voltage"
antus, there was a large change in afr when it changed between the two.
I've found some more info, http://pcmhacking.net/forums/viewtopic. ... 868#p32885 , so I'll keep reading.