D-Jet Fuel Injection Pulse Phasing Options

[Not_A_Six]

Hi All-

I recently installed a 123Ignition dizzy in my '73 2.0. It apparently can be installed in any of 4 orientations, in 90 degree increments and operate properly when wired to the plugs appropriately.

The d-jet version of the 123 dizzy also has two wires that are used to time the two groups of fuel injection pulses (cyl 1+4 and 3+2). These wires can be connected to the ECU in either polarity, and the "correct" polarity to time/phase the injection pulses seems to depend upon both the distributor orientation, and the wire polarity. Instructions from 123 Ignition show a connector sketch that "suggests" a particular polarity, but I think the correct one also depends on the chosen dizzy orientation, as well as the firing order. (The dizzy can be used in non-914 applications. E.g., with a straight 4.)

I'm an EE. I've been through Paul Anders' ( @pbanders ) very helpful writeups on the ECU and d-jet operation. I've got d-jet schematics. And, I've got a generic (Volvo?) chart purporting to show the injection timing WRT the cylinders (which seems to have a lot of discrepancies with a 914 setup with different firing order.) I've also looked at the injection pulse/spark timing with an oscilloscope (with a high-v probe).

It looks like the orientation and polarity can be adjusted to inject fuel at any of the following times:

1) Inject cylinders 1 and 3 during intake stroke and cylinders 4 and 2 during exhaust stroke.

2) Inject cylinders 1 and 3 during power stroke and cylinders 4 and 2 during compression stroke.

3) Inject cylinders 1 and 3 during exhaust stroke and cylinders 4 and 2 during power stroke.

4) Inject cylinders 1 and 3 during compression stroke and cylinders 4 and 2 during intake stroke.

I think the choice of the 4 options above would affect the dwell time of the fuel charge in the intake runners and might also cause some raw fuel to be sent out the exhaust if a pulse occurs during valve overlap.

Which of the 4 configurations is correct? Is my analysis correct, or did I miss something? Any other advice you can give me?

Thanks for your help.

Cheers. (IMG:style_emoticons/default/beerchug.gif)

[914_teener]

The ported vacuum is not "disabled". That is how the advance vacuum signal should work. At idle the port is just past the throttle plate on the atmosphere side so the signal is 0 Hg. As part load starts the vaccum rises advancing the timing signal. Conversely the retard port is manifold vaccum and is highest when the throttle plate is closed.

I.d make sure the dip switch matches your engine config and make sure everything is set up correctly.

If it is you will get a rock steady idle at 800 RPM.

[Not_A_Six]

The ported vacuum is not "disabled". That is how the advance vacuum signal should work. At idle the port is just past the throttle plate on the atmosphere side so the signal is 0 Hg. As part load starts the vaccum rises advancing the timing signal. Conversely the retard port is manifold vaccum and is highest when the throttle plate is closed.

I.d make sure the dip switch matches your engine config and make sure everything is set up correctly.

If it is you will get a rock steady idle at 800 RPM.

Thanks!

I think we're on the same page. By "disabled", I meant that the advance port shows 0 in-Hg vacuum and so doesn't produce any advance at idle because it is above the throttle plate (as you said). I'm aware of how the two ports function WRT throttle position.

Cheers.