123ignition to signal ecu?, or do I need a cranck trigger? Options

[barkamatic]

Purchased a 123 ignition for a D-Jet but due to the difficulty of finding D-Jet parts I have decided to go with an aftermarket system. Probably a silly question, but could I use the FI firing triggers from the distributor for a crank position signal? Thanks in advance.

[dtmehall]

dude;

you have left the reservation!

keep your scalp!

[JeffBowlsby]

Gotta ask, what djet parts are you missing? Your engine year and size and is it stock or modified?

[barkamatic]

the car is a '73 2.0. Stock. I received the car with some Weber 34's on it Bought a D-Jet system off the internet but it was pretty much all junk. MPS wont hold vacuum at all. Mismatch between ECU and other parts. Decided to go with a free standing unit.

[barkamatic]

By the way, I have read pretty much everything you have written. Thanks for the information.

[chmillman]

Bought a D-Jet system off the internet but it was pretty much all junk. MPS wont hold vacuum at all. Mismatch between ECU and other parts.

Really not a good idea, I would never buy used D-Jet parts without testing them or having a right to return if they don’t work. Hope you didn’t pay too much for them…

Putting a D-Jet system together from various used and new parts is possible, but a tricky operation with lots of traps to fall into if you don’t know what you’re doing - and it won’t be cheap either.

There are a couple people in here that have put on “modern” EFI systems, there are some posts on that subject.

[barkamatic]

Bought a D-Jet system off the internet but it was pretty much all junk. MPS wont hold vacuum at all. Mismatch between ECU and other parts.

Really not a good idea, I would never buy used D-Jet parts without testing them or having a right to return if they don’t work. Hope you didn’t pay too much for them…

Putting a D-Jet system together from various used and new parts is possible, but a tricky operation with lots of traps to fall into if you don’t know what you’re doing - and it won’t be cheap either.

There are a couple people in here that have put on “modern” EFI systems, there are some posts on that subject.

I think I can put together a stand alone for about the same price as a new MPS. And I will be working with new sensors, or wrecking yard finds. In other words, cheap. I can use a lot of stuff from the D-Jet: throttle body, runners, air filter, injectors. So not a total loss. I will check out the posts you mentioned. Thanks for your help.

[emerygt350]

I think it would be great to document how you do it, utilizing the 123 as your crank sensor is an interesting idea.

[barkamatic]

I think it would be great to document how you do it, utilizing the 123 as your crank sensor is an interesting idea.

It would certainly be easier. I can't think of anyplace else the 2.0 gets a signal. Maybe I am missing something.I am having a tough time finding the documentation I need to match up the distributor and the stand alone. I did this before on a Toyota Silver Top but that was many years ago. I had to utilize a crank wheel on that one.

[emerygt350]

I think it would be great to document how you do it, utilizing the 123 as your crank sensor is an interesting idea.

It would certainly be easier. I can't think of anyplace else the 2.0 gets a signal. Maybe I am missing something.I am having a tough time finding the documentation I need to match up the distributor and the stand alone. I did this before on a Toyota Silver Top but that was many years ago. I had to utilize a crank wheel on that one.

It apparently sends a signal once per rotation, it's a bank fire system, you would think that would do what you need. Just ignore the second signal.

[dtmehall]

the trigger points on the old D* systems were never meant to carry any current

I have no idea how much your proposed mods would effect all the down steam FI* components

but good luck to you anyway

[Superhawk996]

Probably a silly question, but could I use the FI firing triggers from the distributor for a crank position signal? Thanks in advance.

That is a really bad plan for a lot of reasons.

I’ll list three:

1) uncontrolled backlash between the crankshaft and the distributor drive gear.

2) uncontrolled backlash between the distributor drive gear & distributor shaft that has the trigger points.

3) uncontrolled backlash between the crankshaft and the cam gear.

There are many other reasons but you’ll encounter them as you research the details of the aftermarket ECU you intend to use.

[barkamatic]

Probably a silly question, but could I use the FI firing triggers from the distributor for a crank position signal? Thanks in advance.

That is a really bad plan for a lot of reasons.

I’ll list three:

1) uncontrolled backlash between the crankshaft and the distributor drive gear.

2) uncontrolled backlash between the distributor drive gear & distributor shaft that has the trigger points.

3) uncontrolled backlash between the crankshaft and the cam gear.

There are many other reasons but you’ll encounter them as you research the details of the aftermarket ECU you intend to use.

I had thought of that but I wasn't sure how accurate the stock distributor signal had to be to fire the injectors. Evidently the signal doesn't have to be as steady as I thought. I understand your first and second points but I don't understand your third point. Looks like I will be shopping for a crank wheel.Thanks for your input, guys. I appreciate it.

[Superhawk996]

Bottom line: D-jet injectors are bank fired and shooting fuel into closed intake ports. So not highly accurate.


My third point pertains to FI needs to know crank position and cam position to know when to fire injectors and spark.

In modern FI the cam sensor is driven directly off the camshaft. So cam position is accurately known.

Same for the crankshaft - sensor is usually reading the crankshaft directly.

Position of both the crank and the camshaft needs to be accurate to know when to fire a cylinder.

What you are proposing is (IMG:style_emoticons/default/bootyshake.gif) backwards.

The crankshaft would be inferred across lots of gear lash slop and the absolute camshaft position would be subject to lash (assuming you’re not putting a camshaft sensor directly on the cam somehow). Not ideal.

I’m not saying any of this is impossible, just that inferring crank position via the D-jet trigger contacts isn’t the best design for a FI system.

[barkamatic]

Bottom line: D-jet injectors are bank fired and shooting fuel into closed intake ports. So not highly accurate.


My third point pertains to FI needs to know crank position and cam position to know when to fire injectors and spark.

In modern FI the cam sensor is driven directly off the camshaft. So cam position is accurately known.

Same for the crankshaft - sensor is usually reading the crankshaft directly.

Position of both the crank and the camshaft needs to be accurate to know when to fire a cylinder.

What you are proposing is (IMG:style_emoticons/default/bootyshake.gif) backwards.

The crankshaft would be inferred across lots of gear lash slop and the absolute camshaft position would be subject to lash (assuming you’re not putting a camshaft sensor directly on the cam somehow). Not ideal.

I’m not saying any of this is impossible, just that inferring crank position via the D-jet trigger contacts isn’t the best design for a FI system.

Since I won't know absolute cam position I can't run sequential injection anyhow. I guess I will just have to go to a crank wheel. I thought that since I won't be using the 123 Distributor injector signals to fire the injectors I might be able to use them for a timing signal. But I see what you mean about the tolerance slop. Thanks for your reply.

[JeffBowlsby]

I have no predisposition about custom aftermarket FI (or carbs for that matter), they can be made to be all the things one hopes them to be, given enough time, and $.

One good thing about stock D-Jet is that it is out of the box plug N play. All parts are available still and that should continue to be the case well into the future. Replacing worn out parts is maintenance of a known system which may have challenges these days, but those are not insurmountable.

Consider that custom aftermarket FI opens up a wide variety of unknowns. Correct me if I am wrong, but I am not aware of any aftermarket FI system that is plug N play for our 914s, and that is their Achilles heel. Many of us wish that was not the current situation. They use components that are either generic, or from other vehicles, or are universal in design where they need to be adapted to the 914.

Some of the components may need custom mounts to fit the 914. Some of the electrical hardware does not use waterproof connections, and should not be exposed to our open engine bays. The harness is a major custom component that is very expensive in time and materials to develop and build, to adapt the generic FI to the 914. Once all the hardware is assembled and mounted, the task is to adjust and calibrate the ECU to the needs of the engine. Dyno time or similar efforts. Many who pursue the custom aftermarket FI path also change the engine from stock - displacement, valve timing (cam), ignition. None of this is wrong, but know that the effort and cost required to complete this successfully can be significant, much more than maintaining the stock system, especially if ones time has any value. And once it is complete, then this custom system needs maintenance from time to time, and as it is custom, who has the skills to do that other than the original builder? That can be an enormous devaluation when its time to sell the car. For the right person custom aftermarket FI is the right and maybe the only realistic solution. Just know what you are getting into.

[chmillman]

I agree 100% with @jeffbowlsby about the downsides of having a unique custom EFI on a car you might want to sell later… It will make it more difficult to sell and probably for a lower price as the person who buys it will probably want to reconvert it to something that is understandable and serviceable by more people. Otherwise you will be looking for a unique buyer who is interested in taking over your “project”.

[emerygt350]

My mustangs tbi could care less about position of anything but the throttle (and a bunch of temp and pressure sensors). The computer does play with timing but really only to set the idle. And it knows that through the ignition module on the dizzy.

I bet you could get away with it since firing the cylinder is going to be determined by the distributor. If you keep it bank fire, timing the injection pulse need not be perfect and if that is the only thing the system is using the crank sensor for ...

[barkamatic]

I agree 100% with @jeffbowlsby about the downsides of having a unique custom EFI on a car you might want to sell later… It will make it more difficult to sell and probably for a lower price as the person who buys it will probably want to reconvert it to something that is understandable and serviceable by more people. Otherwise you will be looking for a unique buyer who is interested in taking over your “project”.

With all due respect, evidently our reasons for ownership run along different lines. I am retired and crossword puzzles bore me. I love a challenge, especially when it's technical and I can drive it when I'm done. As far as resale value, I could not care less. When the next owner acquires the car I will probably be dead. Where I live there is not a tuner within at least 150 miles. The fact that I will be tuning it myself by typing into a keyboard is very appealing to me. I didn't mean to take up your time. I was simply hoping that someone could give me an answer as to the output signal of a 123 distributor and the input signal for a stock ecu. Thanks for your time. (IMG:style_emoticons/default/beerchug.gif) Prost!

[Superhawk996]

My mustangs tbi could care less about position of anything but the throttle (and a bunch of temp and pressure sensors). The computer does play with timing but really only to set the idle. And it knows that through the ignition module on the dizzy.

I bet you could get away with it since firing the cylinder is going to be determined by the distributor. If you keep it bank fire, timing the injection pulse need not be perfect and if that is the only thing the system is using the crank sensor for ...

Emory raises a valid point as long as you’re not trying to do sequential and the 123 is handling spark.

The biggest issue is the propensity of these dizzy drives to get installed out of time. But assuming you can pull any of this off, I’ll assume you’re capable of installing the dizzy drive correctly.

Most ECUs are expecting a Hall effect input for the crank signal. The D-jet and 123 is just providing a switched output like the trigger contacts but maybe you “invent” a MOSFET / “one shot” driver to convert to a Hall effect square wave voltage output? (IMG:style_emoticons/default/idea.gif)

As mentioned earlier not impossible but it’s not straightforward either