Injector opening delay

[dcb]

I understand, maybe if you provided some info about indicated and actual refill amounts and related driving style and mileage, something might click.

[smonson]

Will do

[mwebb]

scan data does not measure
ACTUAL injector on time

you can use a high resolution scope .
it is easiest to measure injector open with injector current waveform and it is easiest to measure injector close with injector signal voltage

the open time is about 70% of signal time but varies with different systems



above the Blue trace is Injector current , the red trace is Injector signal voltage - BUT
this waveform was captured using an injector tester pulsing 4ms signals , it is NOT the same as what you will see on a running car / system
BUT
you can see the "gull" in the current waveform which is caused when the magnetic field changes because the pintle has moved opening or closing the injector's opening

an operating system looks like this
pintle movement is clearer and easier to see , this what an actual system waveforms will look like , black is voltage green is current


=================================

Originally Posted by smonson

Hi,

I've built a similar gauge for my '99 Nissan Pulsar (which I think is Almera or Altima or something like that in the USA) after being impressed by the MPGuino when it got mentioned on hackaday. My hardware is similar but totally different software.

My question applies to the OpenGauge/MPGuino as well as my thing. Has anyone actually measured the opening and closing delay of a fuel injector? How do we know it's ~500uS? If the opening time is because of the physical movement of the valve, wouldn't there also be a similar closing delay?

Thanks. -Simon

[smonson]

That's excellent information. So for that Volvo the total delay is around 0.8ms - quite a difference from the Bosch one. That definitely looks like the best way to measure the open/close delay for a given injector.

[mwebb]

hmm yes it is but
i think you are looking for total Open time , the delay itself is only part of the equation as
there is a delay in injector pintle closing as well.

you would need to subtract the delay in closing from the delay in opening and then

use software to subtract that total from total injector pulse width
so the software would know
total injector open time

imho
that is BANK injection , where all injectors squirt at the same time
sequential injection will be similar IN OBD1 systems
but
ThrottleBodyInjection waveforms are very different


that value is going to be different on different system s and
if you are not accounting for
asynchronous pulse , extra fuel at the pleasure of the ECM
you probably should

Originally Posted by smonson

That's excellent information. So for that Volvo the total delay is around 0.8ms - quite a difference from the Bosch one. That definitely looks like the best way to measure the open/close delay for a given injector.

[smonson]

Right. So, if I read the graph axis correctly, 1.6ms opening delay minus 0.8ms closing delay is 0.8ms total delay, subtracted from the pulse width to get the injector operating time.

I'm working on the mathematical approach suggested by dcb now as I don't have a DC current clamp to measure my injector directly.

[mwebb]

since you do have a DSO
Digital Storage Oscilloscope ?

you can use a 1 ohm 10 watt resistor in series with an Injector

since E=I x R or Voltage equals current multiplied by resistance
if resistance equals one E=I x 1 or E=I

or voltage = current , in that circuit , as per OHM's Law

you can connect your scope test leads across the 1 ohm resistor in series with an injector
you will see the SAME current image that i posted for your injector
in voltage
sequential injectors use less than 1 amp so set scope scale to 0 to 1 volt at about .5 ms per division to start then adjust to see image full screen .

place your cursors to get your actual injector on time

[smonson]

Thanks, I know how electricity works. I don't want to go disconnecting everything in the middle of collecting some mileage data, but if I can't get an accurate result this way I will try a current measurement.

[smonson]

Here are the results of my observations

The following maths treat all cylinders as a single measurement. Figures will be 4 times higher than the real value for a single injector.

WARNING: PEDANTIC GUY AHEAD

Tank 1 (country):
- predicted 28405mL
- actually 28360mL (error: 0.15%)
- PWM fired 332468 times for 2195.598 seconds
- average pulse width: 6603uS
- average fuel quantity injected: 85.301uL

Tank 2 (city):
- predicted 30954mL
- actually 30950mL (error: close enough)
- PWM fired 385078 times for 2403.540 seconds
- average pulse width: 6241uS
- average fuel quantity injected: 80.373uL

The difference in pulse widths is 362uS and the difference in fuel injected is 4.928uL. From this we can infer that the fuel pumping rate is 0.01361325 uL per uS. Converting units, that's 204cc per minute which is in the expected ballpark for a small car.

The total time to transmit the average injected fuel amount into the cylinder is then 6266uS (tank 1) or 5904uS (tank 2). This predicts the injector time delay at 337uS for both, depending on how inaccurate those particular fuel pumps were.

Thanks dcb and everyone else for all the advice!

[dcb]

put your car make and model somewhere so folks can use that info pls.