How is an injector actualy controlled?
Turbo Mini Forums

I ask this as the TB injector in my SPi set up is rather noisey, but its not constant.

Whats happening is, at less than 2500 rpm the injector is quiet. over 2500 rpm there is an audiable metalic tap, not dissimilar to an mal adjusted tappet. The rate at which it taps does not rise at the same rate as engine rmp. If you lift off slightly the rate is the same but the tap is less intense. Lifting off completely on over run its quiet. Oh and the 2500 rpm is bang on the button so the ECU is deffo doing something

So, is it at all possible that not only is the Duty cycle being altered but also the current.

Theory being that less current will reduce the opening stroke of the pintle while still at the same duty cycle.

Maybe im stupid, ive not read up too much yet on this, maybe thats how injectors are controled, maybe im talking utter bollox, I dont know. Just thought id share my brain storm with you.

MS

I do not know about the SPi injector but my guess it is the same as a conventional injector, but I stand to be corrected.

Conventional injectors are feed by a 12v live feed, the ecu grounds the -ve to fire the injector. This saves powering the injectors via the ECU.

The injector is just a big solenoid operating a valve and is usually either open or shut.

From an electrical point of view, the current drawn by a device is dependant on voltage and resistance. You feed a given resistance with volts and it draws current. You cant feed current.

Your ECU could vary the voltage, but I very much doubt it.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

wether you power it through the ECU or earth it through the ECU makes no difference. The transistor still needs to handle the current flow of the solenoid!

It does make a difference to back EMF though.

Alex

AlexF

Granted but you can restrict current flow, by increasing the coil resistance??

well you could but pluse width modulation will also do that....

Alex

AlexF

As said - it's either on, or it's off. Adding a resistor will just make it not operate. In theory it will operate slower at a definate point between not working or working - but this gains you nothing?

get a scope and see what your injector is doing

Alex

AlexF