Injector driver patterns Tutorial 1

[Spook1205]

I took some pics of my Fortuna from today's lesson I gave to stage 3 light vehicle students.
first two photos I have put a description of what's going on. Third photo shows the pilot injection gone and just pre injection and main injection.
ill add more in tutorial 2 (doing this on a phone has limitations).

[White One]

so does that waveform show 3 squirts per compression cycle ? I understand the large pulse , and the associated current draw for each , but what does the smaller low amplitude ripple mean? is that back emf from the collapse of the coil current?

[Spook1205]

The large pulse is on for 60 micro seconds, the smaller ripple is alternator voltage on solenoid holding the solenoid on which intern keeps fuel pressure above control needle bleeding off and injector staying on.
The whole pulse width you see on main injection phase at idle is less than .8 millisecond.
I put lots of detail under first pic about injection phases but I realise I can't read it on a phone. So yes it shows 3 injections of fuel for one combustion event.

[White One]

Thanks Luke , I would not have expected alternator ripple so far into the ECU after all the filtering the DC is put through. Excuse my lack of understanding with newer stuff - I trained as an electronics tech ( radar ) in the very early 80's and have not worked in that industry since . Back then the blokes who saw a new 1.8 Camira or a VK Commodore thought it was the end of the world lol.

[Spook1205]

sorry my writing can be confusing, it's not alternator ripple but alternator voltage /battery voltage. It looks rippled due to duty cycle. So the power is turned on and off very quickly. More % it's off the less current draw that's why in tutorial 2 you see the red pattern drop towards end of pulse width.
I wrote lengthy information under the photos uploaded but you can't see it. I will know better next time.
Posting information on forums is not something I have ever done, but I like this community and Fortuna's so I thought I would share. Most Mechanics don't divulge too much but after 30 years of being a mechanic and over a decade of teaching at Tafe I thought I can share some stuff.
I am happy to explain anything I can to people if they want to know.

[Spook1205]

Something also really cool is the current draw is only on every second injection voltage. This is because the injector drivers drive 1 & 4 cylinders together and 2 & 3 are paired up as companion cylinders.
so injector driver supplies voltage to two injectors (say 1 & 4) and then the ECU earthes out the injector it wants to operate hence current draw being a complete circuit.
The Ford Ranger has Piezo injectors and injector drivers supply all 5 injectors the voltage but ECU will only earth outbthe one it wants to work.
I love talking about this stuff so hopefully it interests some people.
cheers, Luke

[White One]

Something also really cool is the current draw is only on every second injection voltage. This is because the injector drivers drive 1 & 4 cylinders together and 2 & 3 are paired up as companion cylinders.
so injector driver supplies voltage to two injectors (say 1 & 4) and then the ECU earthes out the injector it wants to operate hence current draw being a complete circuit.

cool , maybe done that way to reduce the possibility of the injectors crossfiring ? only a guess though. keep the information flowing , im always listening

[Spook1205]

Most actuators (something that does some work, like injector, EGR valve) on engine management systems are earth switched.
By using companion cylinders and earth switching they can reduce 4 injector drivers down to two.
The back EMF from collapsing solenoid coil is actually fed back into injector drive unit (capacitors) for next cycle.
On Piezo style injectors (normally 120v) all current that is fed into them to saturate and expand piezo stack is spat back out into injector driver. That's why I believe they can get away with only one injector drive unit (Hence all injectors get voltage)