D-Jet Fuel Injection Pulse Phasing Options

[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.

[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?

[Not_A_Six]

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?

Thanks, I'll try #2 out. I have the Tangerine kit installed to adjust the MPS, and I've tuned the AFR with an wideband O2 meter. (Yes, I know about the idle mixture knob on the ECU. And, I have the TPS adjusted properly...)

In a bit of an update for anybody searching/reading this in the future, I contacted 123 to find the start and end pressures for the "A" (retard) profile as that information is missing from their instructions for all of the retard profiles.

Their response: "For vacuum retard, the customer needs to rotate the ignition by 10 degrees to retard the ignition. The ignition has the following vacuum map: The retard starts at 80mmhg (3.2 in-Hg) and ends at 150mmhg (5.9 in-Hg) with 10 degrees."

When connected to the retard port on the throttle body, I think this should operate the way I want -- retard 10 degrees at high vacuum at idle, and transition to zero advance/retard as the throttle plate opens and the throttle plate moves below the retard port, causing low to zero vacuum at that port.

But, I wonder if there is some venturi effect at the retard port under part-throttle conditions. If so, the 123 "A" profile may be causing some undesired vacuum retard above idle, but under low load.

Nevertheless, I think that those here chanting "Vacuum Leak" were right after all. I've replaced every hose and gasket, and removed every component to pull a vac on it and test. So far I haven't been able to find it. I'm gonna hook it up to a smoke machine next week and see if I missed something. (Maybe I have a hairline crack in the intake plenum or one of the peened fittings there is leaking...)

My plan now is to find a leak, then switch back to profile #1 (or #2) with vac advance.

Thank you to all who responded.

Cheers.

[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

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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.

[ctc911ctc]

THIS THREAD IS MASTER CLASS!

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[Not_A_Six]

Update for anybody interested:

A special thanks to @JeffBowlsby ! Using his information, I've been able to set up the 123 pulse phasing to match the OEM design, and confirmed with an oscilloscope. It feels like there may be a slight difference in driveability depending on how the FI phasing is set up, but it may be entirely my imagination. The effect seems subtle, if it matters at all.

I did a smoke test to look for vacuum leaks, and it appears that everything is tight. So, I'm now suspicious that the PCV valve is worn and flowing more air than it should (even after cleaning), causing the high idle problem with the 123 "1" profile.

The OEM PCV valve is impossible to find (for me anyway...). And, I'm reluctant to just plumb the PCV to the airbox as was apparently done on later-year models. So, I'm currently in the process of adapting a modern Toyota PCV valve as a replacement. If the Toyota PCV works, I'll start a thread about it as it might be useful to others.

Cheers.

[pbanders]

IMO, if there's a choice on the 123 between vacuum advance or retard, you've got to use the retard. If you don't, when you set the mechanical advance to the stock setting, there's too much advance to bring the idle down to 1000 rpm and the throttle plate closed, even with the bleed screw turned all the way in. I know this is a modified motor with a different cam profile, but I'm pretty sure it would still have the same issue.

Vacuum advance (according to the Bosch Blue Book) is required for low load conditions, where the A/F mixture burns more slowly. According to other references I've seen, this additional advance was incorporated not for better acceleration or transition, but to reduce emissions. Apparently, the improvement in emissions wasn't significant in actual practice, because in later 914's, the vacuum advance port wasn't present on the throttle body and the cell was capped off.

If the vacuum advance is really providing significant driveability effects, it should be a simple thing to test on either stock or modified motors where both the vacuum advance and retard ports are present on the throttle body, and the stock distributor is installed and both cells are functioning properly. Simply clamp the advance vacuum line with a fuel line clamp and see if it makes any difference when driving. I'll try this out with my car when I get a chance.