fuel injector timing (PWM)

[2N3055]

I guess OP wants to do something like this...

As Andreas said, for many years (before GDI) injectors are driven with constant current, and cleverly using injector own inductance to create high voltage for increased voltage compliance for current drive... But before that they used simply 12V and open collector type outputs...  Injector type needs to be known beforehand and proper drive type used.

[old gregg]

Why don't you just put a scope on one of the injector control signals on a real car? That should give you an idea. There shouldn't be any issue, it's just 12 V pulses coming from the ECU.

There's no big difference between cars, the signals are pretty much the same.

I don't have power in the garage to put the oscilloscope on the injectors. Would have been to easy, but that's the ultimate solution if I can't find the proper data. 

actually the project is alive and running, just need to fix two issues : the timing of the injection and a software related issue (stm32).

I guess OP wants to do something like this...

As Andreas said, for many years (before GDI) injectors are driven with constant current, and cleverly using injector own inductance to create high voltage for increased voltage compliance for current drive... But before that they used simply 12V and open collector type outputs...  Injector type needs to be known beforehand and proper drive type used.

indeed, looks a lot like it ! I've to read it. thanks !

[bdunham7]

I guess the OP's questions deserve an answer!

The first reply post from mikerj was the basic correct answer for that type of fuel injection.  However, since I have some actual experience with fuel injector testers, I can tell you that unless you have or can reverse engineer the specs for the particular, exact injector system you are wanting to test, you won't be able to do very much that is useful.  In other words, you have to know exactly how the injector functions in its normal environment and then reproduce that as best you can.

The variety of systems used over the years covers almost every way of doing things that you could imagine.  Here's a few tips on testing injectors.

Electrically, as james_s referred to, there are injectors that function at 12 volts without any current limiting and those that are lower impedance and need current control.  Ballast resistors were a sort of early Datsun 280-ish solution, the way it is typically implemented is to use full current for the turn on (say 1ms) and then use PWM current control after that.  If you can think of a different way to do it, someone has probably done it that way.  High pressure injectors such as modern GDI units have different drive systems and use higher voltage and power.  If you don't closely replicate the original control system, you will get incorrect test results.

Mechanically, injectors can fail in a variety of ways in service and it can be hard to spot some of these on a test bench.  For example, a typical port injector will have a pintle blocking the nozzle that is pulled back by the coil, allowing fuel to flow.  The pintle may vibrate and this helps in atomizing the fuel into a mist.  This pintle vibration may be delayed in a worn or contaminated injector, resulting in a non-atomized stream for the first few ms of operation.  On a test bench with continuous flow the pattern looks OK, but with a 2ms pulse, it isn't. 

I don't think generalized solutions are practical.  If you want advice on the subject, you'll have to be very specific as to what system or systems you want to test.

[langwadt]

Why don't you just put a scope on one of the injector control signals on a real car? That should give you an idea. There shouldn't be any issue, it's just 12 V pulses coming from the ECU.

There's no big difference between cars, the signals are pretty much the same.

I don't have power in the garage to put the oscilloscope on the injectors. Would have been to easy, but that's the ultimate solution if I can't find the proper data. 

actually the project is alive and running, just need to fix two issues : the timing of the injection and a software related issue (stm32).

I guess OP wants to do something like this...

As Andreas said, for many years (before GDI) injectors are driven with constant current, and cleverly using injector own inductance to create high voltage for increased voltage compliance for current drive... But before that they used simply 12V and open collector type outputs...  Injector type needs to be known beforehand and proper drive type used.

indeed, looks a lot like it ! I've to read it. thanks !

I see a flyback diode, that'll give you a very slow turn off. You need a fet that clamps or is rated for avalance at ~40V

[james_s]

I don't have power in the garage to put the oscilloscope on the injectors. Would have been to easy, but that's the ultimate solution if I can't find the proper data. 

Inverters are cheap, and even a small one will power most scopes. You can power it from the car with the engine you're wanting to test.

[m3vuv]

i suppose it depends how wild the cam timing is ,ie valve overlap.!!

[james_s]

No it doesn't. The injector timing has no relation to the camshaft profile, the ECU doesn't know what kind of camshaft is installed, though the cam does affect the optimal fuel mapping.

[robzy]

If you're looking for prior art, check out the Speeduino project:

https://speeduino.com/home/

I used Speeduino as a reference when I was designing my own ECU.