Injector Dead Time Testing

[BennVenn]

A set of refurbished XR6 turbo injectors arrived and with no dead time data that I could find (and what I did find is clearly incorrect), decided to put a few parts together to build up a 12P deadtime table.

You'll need

A fuel rail with injectors and reg
Fuel pump (If your fuel rail is out of your car, just use that - jumper the diagnostic port to keep the fuel pump on)
High sensitivity scales ($10 set from ebay, good up to 200gms)
A bench power supply to adjust the voltage to the injectors
An arduino
2 push buttons and a MOSFET (I'm using IRFB4110 because I had a bag of them, but just about any N channel MOSFET rated at 40v or higher, and say 20amps or higher will be fine - It should also contain a freewheeling diode )

The aduino code is simple, two buttons, one will trigger the injector for a solid 10 seconds. This will give the flow rate of the injector and the fuel weight per second. The second button will fire the injector in 2000 x 5mS bursts. If zero dead time, both weights will match. Calculate the difference in fuel delivered, use this to find the injector dead time (or use my excel sheet). You can adjust the injector time and pulse number if you have super high flow injectors etc.

Repeat at whatever voltages the dead time table in your ecu needs. Only took 20min or so to run through all the voltages 3 times and we've got ourselves a very accurate injector dead time table.

DeadTimeFinder.rar

(688 Bytes) Downloaded 116 times

injector dead time calc.xls

(10 KiB) Downloaded 122 times

[In-Tech]

Thanks very much for sharing.

I will add this to my injector cleaning benches. I have done very little with arduino's. I think I have some uno's around somewhere. Which 'duino did you use in case I need to connect to different pins?

[BennVenn]

Yeah just a Uno, and an old shield proto board I found in the shed.

I can draw up what goes where If you like.

If you used normal sized tactile switches you could code in the option for various injection durations to cater for 100cc/Min up to 4000cc/min or larger/smaller.

[In-Tech]

Way cool, Thanks
I'm excited to try this. When I get to it later this week I am sure I will have some questions.

I am just finishing up my capacitor bridge for fine tuning noise filtration. The automotive environment is crazy at times.

Capacitor_Bank.JPG (50.07 KiB) Viewed 5102 times

[BennVenn]

Interesting! Power rail filtering? If there's specific spikes you're trying to remove an inductor in series with the supply, before those caps will greatly attenuate it.

[In-Tech]

Hiya, mainly what I am fixing is not really noise related but power issues. I'll go into greater detail after testing. Imagine a horrendous environment where power is lost for milliseconds. The ecu resets the baro and blammo it thinks you are at 10,000 ft elevation because it happened during a decel or part throttle. Basically I am using the caps as a "battery" on the ign on circuit. I am also installing a 20,000uf cap on the main batt 12v to clean that before it feeds the dashes and such.

[The1]

Nice work.

Been down all the paths with this which is why i modded code for VS ECU and used that to do all testing. As that's what im using the injectors on!

Alot of help from charlay86 to he's been very indepth with this as well.

Easiest methods ive found is dribble test, run at a voltage, run pressure to spec, then increase pulse width until you get repeatable amounts, i use 10ml, most current gen injectors can do 5-6ml stability repeat, then go through each voltage range.

Other method is do the same thing but with scope hooked up and watch a wide range of the pulse, you'l see when the coil starts to become stable.

In saying this different ecu's all call deadtime different things unfortunately, but i think the main thing at a minimum is to have the same fuel output across the voltage range.

viewtopic.php?f=27&t=7214

Unstable

PXL_20220731_134729994~2.jpg (270.92 KiB) Viewed 5009 times

Stable

[BennVenn]

The1 so you're mapping the nonlinear and linear range of the injectors, not necessarily just the deadtime?

As far as deadtime goes, my method seems very accurate - I can switch between single and double fire and get an identical AFR both down near idle and under load which wouldn't happen unless dead times were dialed in.

[The1]

Difference between single and double fire doesn't have anything to do with voltage offset table, the voltage offset table for example if all conditions are the same but the voltage is different the flow amount should still be the same because of the offset in the table as the injector coil does not operate the same across voltage range.

See attached spreadsheet, you can measure voltage offset another way via 2 pulse widths and measure the output, this was worked out by Charlay86 and then using math give a voltage offset table.

In the other tab you can see the low pulse adder testing and then prediction given and then you can workout the adjustment needed.

[BennVenn]

Please correct me if I'm wrong, this is my understanding:

In 12p, the voltage offset IS the dead time table. Injector dead time changes quite largely with the voltage at the injector.

In double fire mode:
Commanded injector pulse width = dead time + BPW

In single fire mode:
Commanded injector pulse width = dead time + (2*BPW)

For example, if the dead time is 2mS, and BPW=3mS:

Double fire = 2ms + 3ms = 5ms every spark event
Single fire = 2ms + 6ms = 8ms ever second spark event.

The amount of fuel at the valve, every intake stroke will be the same in both modes.

If we get dead time wrong, let's use 1ms

Double fire= 1ms + 3ms = 4ms every spark event
Single fire = 1ms + 6ms = 7ms every second spark event

In this case the actual fuel delivered in double = 2ms and in single = 5ms ( /2 = 2.5ms)

So when ticking the single fire box you'd see your AFRs richen up significantly. This is a simple indication your dead time values are incorrect. I can confirm this is what happens in 12p.

The voltage offset table is simply a way the ecu approximates the dead time at any particular battery voltage.

Injector flow is a constant regardless of voltage, and assuming correctly sized injectors running in the linear range, independant or pulse width. A 10 second continuous flow will give an almost exact flow rate of the injector /min etc.

There is a second offset table in 12p to make the flow characteristics more linear when firing in the nonlinear region.