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Injector setup (find offset table)
Posted: Tue May 12, 2020 5:47 am
by JPh
Every tuner has to setup injector dead time before working on the tune.
I asked the question on the slack channel and Crazy Stricker proposed using a switch between sequential and batch fueling to test if dead time is correctly set.
This method certainly work.
I want to try an other method but I need help to see if it is possible with Rusefi.
The idea is to power only the injectors with a regulated adjustable power supply, so we can see if dead time has a good correction through all the voltage span we need. The feeback is given by a WBO sensor.
But for this to work, we must have a vsense acting only for the injector correction table.
Is it possible to hook an analog voltage input to this table ?
Re: Injector setup (find dead time)
Posted: Tue May 12, 2020 4:24 pm
by mk e
Deadtime or offset is a function of voltage and fuel pressure so you will almost certainly NOT get a good correlation to a point value if you alter these parameters as you're describing.
You can find tables in a few different control scheme formats to see what it should look like at places like this:
http://injectordynamics.com/injectors/id1000/#tabs_20850685925ebab1d269638-tab_3
To keep life simple you just set your fuel pressure, the car's voltage regulator holds voltage constant so deadtime appears constant and you tune. If you want to be able to maintain mixture at varying fuel pressures or voltages you need more tables and need to spend a LOT more time if you don't have the info for your injectors you're using. It's nice to be able to change fuel pressure and not re-tune or have the alternator fail and have the engine run right while you limp home.... (I have these in my setup and had a fuel pump failing and pressure dropped from 58psi to about 10psi before I saw a big change in mixture on my setu) but it does require a LOT more info about the injectors and more time to setup and if you're asking about a deadtime value not table you probably want to be holding voltage constant so it is in fact a value.
Re: Injector setup (find dead time)
Posted: Tue May 12, 2020 5:58 pm
by mck1117
I think that method would work. Repeat the "mode switching" trick at each voltage, and record results. I've done it at two points on my cars by repeating it once with the alternator unplugged, and once under normal conditions.
The method of switching between fueling modes is guaranteed to work because it's making a relative measurement at the same temperature, pressure, voltage, etc by simply changing how many shots we divide the same quantity of fuel in to.
If more shots makes it richer, you're overcompensated at the current voltage.
If more shots makes it leaner, you're undercompensated at the current voltage.
Just switch back and forth between sequential and simultaneous until the AFR matches in both cases, then your deadtime is correct.
Re: Injector setup (find dead time)
Posted: Tue May 12, 2020 6:01 pm
by mck1117
As for this:
JPh wrote: ↑Tue May 12, 2020 5:47 am
But for this to work, we must have a vsense acting only for the injector correction table.
Why? Why not just power the whole car (sans fuel pump, maybe) from an adjustable supply? The EFI system itself only pulls a few amps (average) at idle or light load where you'd be testing this.
Re: Injector setup (find dead time)
Posted: Tue May 12, 2020 6:04 pm
by JPh
Just one difference if you change global voltage you change also the dwell and you make two changes in one step
Re: Injector setup (find dead time)
Posted: Tue May 12, 2020 6:29 pm
by JPh
mk e wrote: ↑Tue May 12, 2020 4:24 pm
Deadtime or offset is a function of voltage and fuel pressure so you will almost certainly NOT get a good correlation to a point value if you alter these parameters as you're describing.
I power only the injector with the variable voltage supply. The pump will have normal supply during the test.
If your point is when I will be in a low voltage status while running the car my pump won't be able to supply nominal pressure, you are right. But under normal low voltage situations the pressure régulateur should be able to compensate. Could be a good test to see how low voltage you can go on the pump to maintain pressure but not so easy to figure out because it's also dependent on the requested flow.
You can find tables in a few different control scheme formats to see what it should look like at places like this:
http://injectordynamics.com/injectors/id1000/#tabs_20850685925ebab1d269638-tab_3
To keep life simple you just set your fuel pressure, the car's voltage regulator holds voltage constant so deadtime appears constant and you tune. If you want to be able to maintain mixture at varying fuel pressures or voltages you need more tables and need to spend a LOT more time if you don't have the info for your injectors you're using. It's nice to be able to change fuel pressure and not re-tune or have the alternator fail and have the engine run right while you limp home.... (I have these in my setup and had a fuel pump failing and pressure dropped from 58psi to about 10psi before I saw a big change in mixture on my setu) but it does require a LOT more info about the injectors and more time to setup and if you're asking about a deadtime value not table you probably want to be holding voltage constant so it is in fact a value.
Re: Injector setup (find offset table)
Posted: Tue May 12, 2020 6:44 pm
by mck1117
There's plenty of ignition energy at idle. You're not going to notice a different going up or down 20% on dwell at idle.
Re: Injector setup (find offset table)
Posted: Tue May 12, 2020 7:05 pm
by JPh
There is no doubt about that.
Re: Injector setup (find offset table)
Posted: Tue May 12, 2020 7:51 pm
by AndreyB
There is a dream of automating this approach
https://github.com/rusefi/rusefi/issues/492 but that's an old dream with not much progress.