EE question...D-Jet related Options

[Mueller]

What I want to do is have 1 12vdc square wave input, with a "splitter" that will alternate between 2 outputs, I want to do this electronically, and not with a Hall type sensor going high or low to reset

[Root_Werks]

I thought I knew the D-jet system pretty well, what would this be for? Edumacate me. (IMG:style_emoticons/default/biggrin.gif)

[lapuwali]

You trying to simulate trigger points? Sounds like you're messing with that new RUNNING car already.

I don't believe the D-Jet really cares which pair of injectors fires on what cycle, just so long as they alternate. If that's so, it makes the problem a lot easier. If the D-Jet runs like crap with the signals 360d off, however, you'd need more than just a plain square wave in to make this work.

Assuming you don't have to worry about position, just alternating, you'd need something like a flip-flop to provide the alternating, and I'd use a pair of transistors (one for each output). There are some unanswered questions like what's the dwell on the trigger points, and does it matter? Do we need a variable-width pulse based on engine speed, or is just a fixed-width pulse good enough? No idea what the D-Jet ECU does with the trigger points pulsewidth, if anything.

[bondo]

http://www.fairchildsemi.com/pf/MM/MM74C374.html

Maybe this one would work? I think one flip flop would just turn one output on if the input gets a pulse, and off if it gets another pulse, and so on.. But this puppy has 8 of them, perhaps some combination of them along with an inverter might do the trick? Sorry, I'm not an EE, nor do I play one on TV.

[davep]

This thread is useless without more data.

A square wave can be easily generated, then add an inverter as the second output.
The next question is: what frequency?
Then there are a whole bunch of other questions.

Can't be for injectors. 12V is too much for them. Also pulse length is critical. The computer takes a basic pulse train and modifies the hell out of it according to sensor inputs.

[bondo]

I *THINK* he is trying to modify a basic tach signal to feed to the djet computer so he can run a non-stock distributor, or something like that. That would mean the frequency would vary from about 15hz to about 100hz. The issue of dwell is probably important, the ECU may not like it if one signal was always on, and just alternating. Pulling it off would require an intimate knowledge of the djet ECU. I don't even know what voltage the trigger points are switching. If dwell is important, then it could get complicated really fast. The on time would have to be adjusted based on frequency, which can change. I agree, more info is needed (IMG:style_emoticons/default/smile.gif)

[Mueller]

yes to a bunch of the questions (IMG:style_emoticons/default/smile.gif)

trying to eliminate the trigger points in the base of the distributor for the D-Jet

with the L-Jet, all 4 injectors fire when the coil collapses, with the D-Jet, there is a cam lobe on the dizzy shaft that in normally open, right before the intake opens, the contacts touch, sending a small 12vdc signal to the ECU, the ECU then grounds the injectors firing one pair (every ignition cycle one or the other contact closes completing the loop)....very small amperage amount from what I have read, less than the contact points driving the coil.

not sure if the ECU cares about dwell or not, it could be as simple as on/off, same as the L-Jet, as long as there is a voltage differantial, the trigger works

[McMark]

I think there is a small amount of time when both triggers are being switched.

Interesting project.

[lapuwali]

not sure if the ECU cares about dwell or not, it could be as simple as on/off, same as the L-Jet, as long as there is a voltage differantial, the trigger works

Maybe, maybe not. The whole D-Jet system is basically too clever by half, and obvious designed by someone who knew analog voodoo much better than I do (which ain't hard).

Without a good scope and lots of time, there's no real way to know. I'd think that you'd be right, and simple pulses would work. Only the frequency really matters. However, I'd also not expect the MPS to work the way it does, either.

The square wave generator and inverter idea might work. Feed the input square wave into a divide-by-two frequency divider (crib circuit from one of many Radio Shack handbooks), and pass that signal straight to injector pair A, then invert the signal and send that to injector pair B. This assumes the square wave in has a pulse every time a spark fires. Where are you getting the square wave from? If it's the coil trigger, you might have a problem with the flyback voltage, just like the MS tach input.

[pbanders]

not sure if the ECU cares about dwell or not, it could be as simple as on/off, same as the L-Jet, as long as there is a voltage differantial, the trigger works

Maybe, maybe not. The whole D-Jet system is basically too clever by half, and obvious designed by someone who knew analog voodoo much better than I do (which ain't hard).

Without a good scope and lots of time, there's no real way to know. I'd think that you'd be right, and simple pulses would work. Only the frequency really matters. However, I'd also not expect the MPS to work the way it does, either.

The square wave generator and inverter idea might work. Feed the input square wave into a divide-by-two frequency divider (crib circuit from one of many Radio Shack handbooks), and pass that signal straight to injector pair A, then invert the signal and send that to injector pair B. This assumes the square wave in has a pulse every time a spark fires. Where are you getting the square wave from? If it's the coil trigger, you might have a problem with the flyback voltage, just like the MS tach input.

You might want to look at my analysis of the D-Jetronic ECU:

http://members.rennlist.com/pbanders/ecu.htm

I'm not exactly sure of what Mueller wants to do or why. The trigger contact points are probably one of the more reliable parts of the system, you only need to change them every 100K miles or so. The failure mechanism is usually not the contacts, but the phenolic blocks that ride the cam wearing down so much that disrupt the timing of the two switches and the overlap period.

[lapuwali]

I'm not exactly sure of what Mueller wants to do or why.

I think he wants to run a distributor other than the D-Jet unit, like a Mallory Unilite.

I'd looked through your site quite a few times, but don't remember seeing so much data on the ECU before. Looks like only the opening (or is that closing?) of the trigger points is used, so dwell isn't accounted for. Or I completely misread that (which would be easy). Lots of data there.

[davep]

The trigger points create a fairly short pulse. Shorter and closer together as the RPM rises, and of course timed to the crankshaft rotation. I'm not sure how to create a signal EXACTLY matched to the RPM without a direct link to the crankshaft. Trigger points, ignition rotor, crank position sensors all are linked to the crank. Think how crappy the engine runs when the distributor is not timed correctly, or the dwell is not correct. The factory way is simple and reliable.

[bondo]

Now that I think about it, the two trigger points have one lobe, the ignition points have 4. So to youse a tach signal, you not only need to flip flop between two outputs, but you aslo need to divide by two. Also, aren't the trigger points set up such that the injector opens when its intake valve is open? I think that would be impossible to get out of a tach signal.. if you could get that, it'd almost certainly involve a dead cat. (IMG:style_emoticons/default/smile.gif)

[bondo]

I know you wanted to avoid a hall type sensor, but what if you put an induction timing light sensor on the plug wires for cyls 1 and 3 (or 2 and 4, whichever is closer to what the trigger points do).. then you can make each bank trigger at the correct time. Eh, nevermind, my cheesyness alarm just went off. There's no way to make such an installation elegant (IMG:style_emoticons/default/smile.gif)

[TheCabinetmaker]

Also, aren't the trigger points set up such that the injector opens when its intake valve is open?

Nope. The injectors open two at time with the fuel ready and waiting for the valve to open.

[JeffBowlsby]

The trigger points only tell the alternating pairs of injectors to turn ON. Thats all they do.

The ECU then calculates the pulse width based on the other sensor data to turn them off.

Leave the deer killer with all four corners on the ground Mike...

HEY YOU THERE...YES YOU...PUT DOWN THE TOOLS AND STAND AWAY FROM THAT 914....

Unless of course you are going to drive it....(IMG:style_emoticons/default/biggrin.gif)

We love you man.... (IMG:style_emoticons/default/wink.gif)

[bondo]

Also, aren't the trigger points set up such that the injector opens when its intake valve is open?

Nope. The injectors open two at time with the fuel ready and waiting for the valve to open.

Huh, I guess you'd have to do one at a time to inject while the valve is open. Why the extra complication of doing two at a time and not all 4 at a time? Too much fuel pressure drop?

It sure is fun to think about this stuff (IMG:style_emoticons/default/smile.gif)

[TheCabinetmaker]

Royce, I try not to think why. It just confuses me. (IMG:style_emoticons/default/wacko.gif)

[Mueller]

James is correct...Mallory Unilite distributor, has no "stock" method of triggering the trigger points

Jeff...thanks for the confirmation on the trigger points, I took them as just a simple signal for the ECU to fire the injectors

good news...my wife likes the new 914, wanted to go out to dinner in it until I mentioned "no heater"...I'll have to fix that very soon (IMG:style_emoticons/default/smile.gif)

[scotty914]

why not just put a pick up on the fly wheel to trigger the signal, making a circuit to transfer a hall or VR sensor to make or break a connection is easy. the hardest part is getting it to only do it on every other rotation . or you could use a pick up in the dizzy, that you add in. i would assume that the points are 180 out of rotation to each other. it could be as simple as 1 very small reflector glued to either side of the shaft or rotor with two small optical pick ups ( basicly avalible as one led looking thing ) either drilled in to the dizzy body or cap, this puts the pick ups 180 out of phase if the pick up are 180 apart.

a little harder ( but not much ) to do would be as some one said install a pick up on one spark plug wire to trigger a circuit to average the signal and trigger two transistors per spark or two pick up and just build 2 seperate triggers. and it could be done with 3 small wires to the spark plug wires. no large clamp like a timing gun needed, just a loop or loops on the plug wire

any of the above systems could be built as an add on board that the injector points wire just plugs in to. and it could be sold once worked out. i think price to make this board would be 20 to 30 bucks