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By digmorepaka
#49549
Hi, I just thought I'd share this injector dead time tester I made. It produces an adjustable pulse and has a voltage readout to determine injector dead time opening time at particular voltages.

I will be posting the code and schematic very soon!

Image

EDIT: Currently spending a lot of time getting my project car fully working, so it will take a bit to publish the schematic and code. I will be publishing it once i add pulse count function to determine the true dead time not just open time(thanks to the guys who commented pointing out that I mistook one for the other)
Last edited by digmorepaka on Sun May 02, 2021 10:50 am, edited 1 time in total.
By digmorepaka
#49560
NickZ wrote:
Sun Apr 11, 2021 10:10 pm
How does it calculate the dead time?
It creates an adjustable pulse length(seems to have a precision of roughly 10 microseconds) and you watch for the injector squirting a small amount of fuel out.
By moonie223
#49567
The only way to maybe do it correctly without measuring fluid volume is by watching coil current, which will waiver as the needle starts to move. Trying to ride the injector right on the deadtime is not a useful measurement for anything. That's not how it works while it's on the car. You need to fully open and close the injector, not bounce it off the seat.

If you made something that can pulse the injectors reliably and you've got a rail feeding pressure and you're sure you won't light your ass on fire, then measuring volume is what you and the ECU actually wants. You are already 99% towards something useful, may as well close it off. Just run 20%, 60% 80% and 100% duty or so and measure the difference between results to find the actual deadtime. If you have a ECU that can, you can even start figuring small pulsewidth corrections.

If your injector driver isn't damn near identical to whatever you are using in the ECU then you are kinda wasting time. Better hope you don't have a flyback diode on there at the very least.
By digmorepaka
#49570
moonie223 wrote:
Mon Apr 12, 2021 8:04 pm
The only way to maybe do it correctly without measuring fluid volume is by watching coil current, which will waiver as the needle starts to move. Trying to ride the injector right on the deadtime is not a useful measurement for anything. That's not how it works while it's on the car. You need to fully open and close the injector, not bounce it off the seat.

If you made something that can pulse the injectors reliably and you've got a rail feeding pressure and you're sure you won't light your ass on fire, then measuring volume is what you and the ECU actually wants. You are already 99% towards something useful, may as well close it off. Just run 20%, 60% 80% and 100% duty or so and measure the difference between results to find the actual deadtime. If you have a ECU that can, you can even start figuring small pulsewidth corrections.

If your injector driver isn't damn near identical to whatever you are using in the ECU then you are kinda wasting time. Better hope you don't have a flyback diode on there at the very least.
Adding an opening count option and measuring the injected volume should let me calculate the correct dead time, which would make it accurate. Going to work on that.

Switching circuit has extremely close properties in terms of delays and resistances compared to my target ECU. There is no flyback diode, ECU doesn't have one so it would screw it up compared to the target application.
User avatar
By PSIG
#49619
digmorepaka wrote:
Mon Apr 12, 2021 11:17 am
… do I understand it correctly that the inaccuracy comes from not incorporating the closing time?
No, dead-time (injector latency) measured by flow-testing contains both opening and closing times. A live setup should assume using both values, as that is what is seen during real-world operation. During the pulse-width, fuel flow is reduced while waiting for the opening, but fuel is still flowing (added) while waiting for the injector to close after the end-of-signal. While the separate values are useful for other purposes; the combination of both values is how we arrive at useful "dead-time" when operating.

As a side-note, many other factors can play into latency besides voltage, such as fuel pressure or current capacity*, so be sure to rate, graph or compare with all the same parameters. Many online references fail to include factors such as rail pressure and inadvertently ends with inaccurate results. Likewise, the injector usually flows differently at low pulse-widths (non-linear flow range), where latency values are not correct. So, be sure to stay out of that range unless intentionally testing for the variation.

Finally, and no matter how awesome the bench tests the final results are what count, and so testing latency on the running engine is always a good idea. Because I always test running latency, I only use latency references or defaults as a starting point, to be tuned in the real-world. If any running parameters are different than tested parameters, then tuning tests are a requirement. For basic tuning tasks with typical injectors, dead-time tuning makes injector bench testing unnecessary for most users.

* If using a small battery or power supply, the supply voltage may read correctly when unloaded, but actual voltage and current drops when the circuit is loaded. Verify your test conditions relative to installed/running with a 'scope before relying on the results. ;)
By moonie223
#49630
My injectors drift super hard with heat. 1100CC at 4 bar, "deadtime" around 1ms when it's stone cold and a deadtime closer to 1.4ms when it's stupid hot after sitting for a few minutes to an hour. After it cools off or cycles plenty of fuel it calms back down.

Since my injectors are so damn big it gets to being a serious pain in the ass to keep fueling right at low loads. 0.5ms is more than a quarter of the entire fuel pulse around idle.

While fuel density might have something to do with it I doubt it's all of it, manly because priming the return pump for a while doesn't change anything.

Besides all this, measuring deadtime by switching pulse counts on a running car has always ballparked it enough for my needs.
User avatar
By jonbill
#49632
That might be part of the problem I have with heatsoak on mine, although mine did get a fair bit better with a return on the end of the fuel rail.
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