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]

I installed the 123 with stock D jet as shown per the installation instructions and it performed flawlessly. I indexed and installed it as was the stock dizzy...meaning clocked the same way.

I have since sold the car so I never really experimented with it in the aspect that you are suggesting.


Good luck.

[Not_A_Six]

I installed the 123 with stock D jet as shown per the installation instructions and it performed flawlessly. I indexed and installed it as was the stock dizzy...meaning clocked the same way.

I have since sold the car so I never really experimented with it in the aspect that you are suggesting.


Good luck.

Thanks. I think the #1 plug wire on the OEM dizzy is supposed to be just clockwise of the vacuum dashpot and is in the 11 o'clock position in the engine bay when looking down at it from the rear of the car. But, there is no dashpot on the 123. How did you clock it to match OEM? I guess you could align the retaining straps, but that still gives you two orientation choices.

Also, I think it will run "good enough" with any orientation and polarity. But sadly, I'm hopelessly obsessive -- I'm looking for "best", and wondering how it was designed to work. (IMG:style_emoticons/default/idea.gif)

From a design standpoint, I think you'd want to avoid injecting during the intake stroke, as (I think) that would create asymmetry among the cylinders, and also inject fuel during the valve overlap time. I dunno. Maybe it doesn't matter... (IMG:style_emoticons/default/confused24.gif)