Diesel Conversion

[bgsengine]

And to time the pump I was thinking of maybe setting up a crank trigger.

It can be done, the trick really would be getting the timing right, plus something to power the injector.

Look at any automotive Hall Effect Sensor and you can probably rig a sensor and bracket to time off the flywheel magnet (or drill a hole and a trigger pin in the flywheel where required) Some sensors may work off leading edge, others off trailing edge, then you will need the controller to tell the solenoid in the injector when to fire, and for how long to remain open vs how long to remain closed (The duty cycle). (that affects fuel-air mixture ratio, and also must take into account the system pressure, which really should not vary, so you need pressurized system plus a pressure regulator) You could do a "limp mode" where the duty cycle is pre-set for certain RPM ranges , but that results in waste and horrible fuel efficiency, so you will need to have a mass air flow sensor to determine air volume, and possibly a throttle position sensor to determine throttle opening... Or, a Mass Air Flow sensor and Air Temperature Sensor. So as you can see, Electronic fuel injection *is* possible, but you'll need to do a lot of R&D to get it right.

[John_Forbush]

If the Hall effect sensor was rigged to the flywheel wouldn't opening up the throttle butterfly up the rpms of the motor therefore making the magnet pass by the sensor more quickly and in turn make the injector put more fuel to the engine?

[bgsengine]

If the Hall effect sensor was rigged to the flywheel wouldn't opening up the throttle butterfly up the rpms of the motor therefore making the magnet pass by the sensor more quickly and in turn make the injector put more fuel to the engine?

Yes, and No.

More Fuel as in injector opens more often. But, fuel *per squirt* would not change until you change either the duty cycle, or the fuel rail pressure, and it is that "per squirt" fuel delivery we need to be concerned with - you have to set it for the proper duration, based on the fuel pressure, so that it delivers the correct amount of fuel to the air stream. A carburetor does that by way of jetting, but an electronic fuel injector cannot do that- it must be turned on, and off, and it can not simply directly switch in relation to the trigger signal It needs to be controlled to deliver a precise amount of fuel depending on : Air Temperature, Air Volume, Engine Temperature, and Fuel Pressure - it needs to match up with those factors to achieve the fuel efficiency you are looking for. WIthout the control loop and sensors, you'd be flying blind as mentioned, or "Limp In" mode, but even for THAT you are still going to need to figure at least the needed duty cycle of the injector to deliver a reasonably close/average fuel rate to the air intake.

[John_Forbush]

When the engine rpms go up the amount of times the injector squirts would go up, it wouldn't need to change the amount of fuel would it?

[bgsengine]

When the engine rpms go up the amount of times the injector squirts would go up, it wouldn't need to change the amount of fuel would it?

Yes, because in order to increase the RPM, the throttle has to be opened more, allowing more air into the system, thus, a need to increase the amount of fuel injected to the air to maintain stoichometric ratio - Given a fixed injector squirt (On Time of the Injector) with a fixed fuel pressure, you will get a fixed amount of fuel. If you can get the injector to squirt just enough fuel to make stoichometric ratio at mid range RPM, then without changing the injector duty cycle or fuel pressure, then at idle, the mixture will be rich, at top no load, the mixture will be lean, and you will have really lousy (and slow) acceleration, if it accelerates at all.

In order to have properly working fuel injection, you need to be able to control the injector duty cycle OR the fuel system pressure precisely (duty cycle measured in milliseconds) The injector will squirt more often as the RPM increases, but you also need to be able to increase or decrease the *amount* per squirt to match the incoming air volume.

[bobodu]

Not too familiar with FI...but won't you have to increase the pressure too?

[bgsengine]

Its actually an either/or, but can be both - with EFI, it is usually easier to maintain a constant pressure using a regulator, and vary the injector pulse width (on time) or duty cycle to adjust the amount of time the injector is open at the known fuel pressure to precisely meter the right amount of fuel. at idle, an injector may only be open for 0.8 milliseconds, , on acceleration, it may open for 2 milliseconds, and as it revs up and reaches desired RPM, injector may be switched on for just 1.3 milliseconds - the on time regulates the amount of fuel that is squirted at a given pressure.. There are some systems that vary the pressure instead of injector on time 9or in addition to), but it is much more difficult to precisely vary a fuel system pressure than it is to precisely control an electronic component.. again note we're discussing automotive style indirect injection into an intake manifold or pre-combustion chamber before the intake valve, not direct injection into a pressurized combustion chamber... (which requires a *lot* more fuel pressure)

[bobodu]

I meant more pressure than what he probably has now....gravity or a pulse pump wouldn't be enough...right?

[bgsengine]

I meant more pressure than what he probably has now....gravity or a pulse pump wouldn't be enough...right?

Oh yeah that is true, though FI can work on lower pressures like 8 PSI or so, but it does need to be regulated so as to maintain a steady, consistent pressure so gravity feed is definitely out, pump feed *might* work depending on the pump, but would definitely need a regulator and return line.

[John_Forbush]

What kind of a sensor would I need to regulate my injector?