Fuel Injection Controller

Its not difficult to build a variable frequency PWM to do exactly what you want it to. Plans are available Via the all expansive interwebs, and can be found with a quick google search. Or if you'd rather, I'd wager some that you can buy one pre-built.

So i just hook up a pwm to an injector and turn up the frequency?

A standard PWM does not change the frequency, only the length of the "On" cycle. PWM = Pulse Width Modulator

Your looking for a variable frequency drive with a pulse width modulated signal.

you need Frequency modulation, which can be a quick add on to a standard PWM to give you the ability to change the frequency, while still giving you the ability to control the length of time the injector will be in the "ON" mode. This information can be found all over the net.

http://www.robotroom.com/PWM.html

http://en.wikipedia.org/wiki/Variable-frequency_drive

http://www.joliettech.com/what_is_a_variable_frequency_drive.htm

http://www.driveswarehouse.com/Drives/AC+Drives/Variable+Torque+VFD/X200-002NFU.html

or you can just buy one already made... ~100 bucks should get you something that can work, with little to no modifications.

So the fuel injector needs 12 volts and the frequency is the opening pulse and the step is how long it stays open?

I have never seen a pwm that does all 3. Most control voltage and step i think. I have some that only control voltage. I have one that controls amps and voltage, but I dont know how it controls amps. I have never taken it apart and looked at the board. It has 2 dashpots, but that is all i know about that one.

I really don't want to spend any money making the test rig. I just want to use a pwm to operate an injector. I think I can hook up a microswitch on the positive leg to pulse the injector without the pwm, but that will not work by itself. Also I was not sure what voltage the injector uses, but I think it is 12 volts.

Thanks for the links, I will check them out.

So the fuel injector needs 12 volts and the frequency is the opening pulse and the step is how long it stays open?

More or less. The frequency is the rate of pulses sent to to the ECU that correspond to engine speed. At a fixed engine speed the frequency is roughly fixed. The pulse width is the time from the start of each pulse to the end of each pulse, which is the injector open time. Pulse width directly affects mixture. The actual injection start point is not generally the same instant as the pulse sent from the crank position sensor, but in a simple system, it could be, or at least the delay could be fixed. (The ecu can make the injection start point vary all over the place, relative to crank position, just as the ignition timing varies all over the place.)

Yes, most injectors are 12 volt, and some require a resistor -- look on the web for injector resistors. Ordinarily, the pulse is on the ground side -- in other words the injector is fed +12 volts all the time, and the ground lead is interrupted by the ECU. The injector is either open or not, so voltage does not matter much: 10 works as well as 15, in other words it is the open time (per intake stroke) that affects mixture.

A timer module, like a 555, allows you to set frequency with one resistor (and cap) and pulse width with another. If you wanted to run a single cylinder engine, you could pulse an injector at a high rate, and control just the pulse width to control mixture, not worrying about injection timing. You'd have roughly the equivalent of older constant injection systems, or an electronically controlled carburetor. Any fuel injected during the valve closed time would get sucked in on the next valve opening.

Most IC's like a 555 can't handle the current required to pulse an injector, so you'd need a power transistor (or possibly even a small fast relay, if you are only experimenting) to handle the actual current -- the 555 would only supply the signal. The power transistor would need to be protected from transient spikes that the injector coil creates -- they reach more than 60 volts, typically. At this point the circuitry becomes a little more complicated -- but the basic idea is very simple.

A 555 timer can also be triggered to time for an interval. You'd have to look up a data sheet, but I think you could trigger and retrigger intervals easily fast enough for each interval to be started by a pulse from a camshaft (or anything that moves at half engine speed) sensor, and for the length to be controlled by a pot attached to the 555. In real life, the length of the pulse would not be controlled by a pot, but would be controlled by modifying a table value with calculated values based on intake air temperature, water temperature, and mass air flow (which could be based on manifold pressure) and (especially) O2 sensor reading. If you were really interested, you could do the logic with a small microprocessor , like a basic stamp.

All sorts of possibilities, the easiest of which is to buy a Mega Squirt, etc.

The injector itself needs to be sized right, or it either cannot be pulsed briefly enough to avoid a too rich mixture at low load, or cannot flow enough to provide enough fuel for full output.

Ok, you may be better off purchasing a 2nd hand Car computer, giving it a pulse train of varying frequancy on the "Tach" input, and varying the voltage with a POT or something on the Accel input...

For testing of the Injection setup for my Off Road car, I connected a variable speed hand drill to the input shaft of a Dizzy, the wiring for the reluctor pickups twisted to the wiring of the dizzy, and turned it on, varying the drill speed gave me what was needed to drive the injectors, including the saftey circuits, as the injection switching pulse is not really a direct On-Off type pulse like on motors, they have peak and hold controls for the currents, also some injectors are low impediance, and some are high, the low ones may need to have a series resistor to limit their current...

Check out the wiring information on the LinkECU web site shoud help ;o)

http://www.linkecu.com/products/engine-management-ecus/g4-xtreme

Bottom of the page under "Downloads" -> "Download the G4 Xtreme instruction manual"

I'm using the G4 - Extreme in my Buggy.. and am currently working on the wiring and ECU configuration, but for you, just go to the wreckers and see about picking up a old ECU and wiring loom ;o)

I have an old porsche donor. I have a spare ecu for it. You think I should use the ecu to fire the injector with a pot?

If so, I would need to know how the ecu is wired for power. I think I have a schematic for the car from a Haynes manual, if not, I can get one. I don't know if it shows the ecu wires though in the circuit. I could trace the inputs to identify knock sensor, crank sensor, etc. In order for this to work off of a vehicle I think I will have to have all of the inputs required for the engine to run within range to start. I think the injectors will fire if there are inputs from crank, tach, tps and power/ground. If I missed something tell me since I have never tried to use an ecu to do bench testing. It has a distributor so I could fire the injector by hand with that or run it with a drill motor. I actually have a test fixture made up for points distributors to experiment with spark so this will be very similar.

Thank you for your input.

Ok, the CAS (Crank Angle Sensor) doens't need to be on the crank, it can be in the dizzy, or you can supply the pulse train differently, this pulse is only needed as "1 pulse per engine rotation, so you can have a dizzy with 2 pulse trig's per dizzy rotation, the dizzy I'm using is a Toyota AE86 (or is it 96) electronic "Reluctor" type, this has 2 levels, a "Tach" (lower) and a Index (Upper)

Knock is not needed, its only there for the ECU to detect "Pinging or Pre Ignition"

Don't worry about temp sensing, the Accel, you can wire up 2 resistors as a voltage divider, set to 50% throttle, So, with low engine speeds, you'll get almost 100% "ON" time and high a shorter ON time once you go over 50% Dizzy speed.

You could also look on the net for "After market fuel injection" there is a kit for a Injection system out there, and you could just be after the driver chips.