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)

[rjames]

I have a 123dizzy and wasn’t able to get idle rpms below 1000 using either the advance of retard settings and at least one other person here had the same experience, IIRC. If you can’t get below 1500, something else is wrong. How was your idle before installing the 123?
Have you checked the throttle body air bleed screw? Sounds like a vacuum leak or timing is off.

[Not_A_Six]

I have a 123dizzy and wasn’t able to get idle rpms below 1000 using either the advance of retard settings and at least one other person here had the same experience. That said, if you can’t get below 1500, something else is wrong. How was your idle before installing the 123?
Have you checked the throttle body air bleed screw? Sounds like a vacuum leak or timing is off.

Thanks for your comment.

The whole idle/retard discussion is kind of tangential to the original FI phasing questions that I started the thread for.

Nevertheless, it's interesting, and may be helpful to somebody else down the road.

I *can* get it to idle just fine at around 1000 rpm with the 123 vac retard connected and profile "A". With profile "1", I couldn't get it below 1500 rpm. I figure that under idle conditions (no centrifugal advance, throttle plate closed) that profile "A" gives a net idle timing of -5 degrees (which matches OEM) and profile "1" gives a net timing of +5 degrees. I attribute the elevated idle with profile "1" to that difference in timing. But, I don't rule out that something else may be in play (e.g. an undetected vacuum leak as has been mentioned.)

FWIW, this is not a stock engine. It's a 2056 with a webcam 73 cam. But, I don't believe this is the primary cause of the high idle with the vac advance profile.

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

[Frank S]

FWIW, this is not a stock engine. It's a 2056 with a webcam 73 cam. But, I don't believe this is the primary cause of the high idle with the vac advance profile.

You want to use vac advance with this engine. Setting #2 the engine likes to idle between 950 and 1000 RPM with 10° to 12° BTDC at that engine speed. If the RPM's are to high you probably have a vacuum leak or running to rich. Did you try to lean out the idle mixture?

[914_teener]

[quote name='Frank S' date='Jul 16 2020, 11:55 PM' post='2834494']
FWIW, this is not a stock engine. It's a 2056 with a webcam 73 cam. But, I don't believe this is the primary cause of the high idle with the vac advance profile.

You want to use vac advance with this engine. Setting #2 the engine likes to idle between 950 and 1000 RPM with 10° to 12° BTDC at that engine speed. If the RPM's are to high you probably have a vacuum leak or running to rich. Did you try to lean out the

(IMG:style_emoticons/default/agree.gif)

And so you would ajust the static timing and run the vac advance.to the 123 and not manifold.vac


I asked if it was a stock engine a while ago.

[Not_A_Six]

...And so you would ajust the static timing and run the vac advance.to the 123 and not manifold.vac...

Yes. Clearly.

When running an advance profile on the 123, I've connected it to the advance port on the throttle body; when running a retard profile, I've connected it to the retard port. Unused ports have been plugged in all cases.

Sorry if I didn't make this clear earlier. I thought it was understood.