More knowledge needed please.

[Guest]

I've read just about everything I can about signal generators and igniters in my effort to find a replacement ignition for my 83/550 project but I seem to be missing a clear understanding of how they all work together.

Basically I understand that the signal generator (pick-up coils) send a signal to the igniter to turn the coils off and on which generates the power to fire the spark plugs.

What I'm failing to understand is how the pick up coil generates this signal and what amount of voltage is sent to the igniter. As one of the igniter tests calls for running a screw driver blade in front of one of the pick ups to test for spark, it must be a very weak voltage.


Also, somome pick up coils have one wire each and a common ground wire to the igniter with the more modern ones have 2 each and a seperate ground I believe (yellow/ green) that connects to the wiring harness close to the igniter. How does the two wire pick-up work? Does it send 2 signals or is it one signal into the box and back out in a loop?

I also wonder about the igniter signal to the coil. I know that the power to the coil is "on" all the time and the transistors in the igniter turn this off on receipt of the signal from the pickup coils which then causes the coil to deliver power for spark. What confuses me in my readings is references to power for the igniter. As far as I can see it is not powered but recieves voltage from the coils. Am I understanding that correctly?

What I'm trying to come to grips with is why my test igniter/signal generator from a 750 is not creating a spark. The signal generator specs out at the correct resistance, the igniter checks out in my running 750 and the coils are powered and show correct resistances. All things being equal there should be spark.

If someone could help clarify this all for me I might be able to suss out where I'm going off the track. So far all I can think of is that there is some issue in the wiring harness itself so my next step will be to try the igniter trigger test using the ohm meter and if that doesn't show anything then I'll wire the out pins directly to the coils and bypass the harness.

As always all input is greatfully appreciated. As I've often found, sometimes even the most off the cuff statement can lead to the Eureka moment so feel free to add your comments.

Cheers,
Spyug

[Billy Ricks]

Voltage to everything should be 12 volts. What you measure when testing the signal generators is resistance. The two wire generators just have separate wires in instead of a shared source. The igniter sends a constant signal to the generators which then complete the circuit as the rotor rotates to it. They only send one signal per revolution. On a 4 cylinder GS the plug fires every stroke on the cylinders that share the same coil.

The igniter is powered. Since it's isolated from the chassis it has both + and - in. Then a negative out for each coil. It actually completes the ground to the primary side of the coil causing it to fire.

[posplayr]

I'll keep it simple

1. There is always 12V applied to the + side of the coil, but the only time current flows through the coil is when the negative side is shorted to ground.
2. The spark occurs when the magnetic field built up in the coil (from the current) collapses or current stops flowing. That is when the short on the negative side is removed.
3. The igniter has a transistor or FET at it's output which is what either shorts or opens the ground to the coils. When the igniter output stage Transistor is OFF (open) no current flows. When the transistor is ON (closed) current is flowing.
4. The igniter times the ON/OFF of the transistor using small voltage pulses from the pickups. The pickup acts like a little generator (kinda like out 3 phase generator). Think of a magnet moving paast a small coil of wire. This causes a little pulse of current that the igniter senses and amplifies to ON/CLOSE the output stage. The electronics in the igniter needs some power to run the detection circuit and drive the output transistors.
5. If it is not clear, when the igniter shorts a output stage, then current flows from the charging system, through the coil and is sunk to ground into the igniter output. This is low side control, so there is really no signal sent to the ignitor. It is the opening and closing of a low side switch.

Now it is possible the pickup is a variable reluctance device, meaning it acts like a proximity sensor and pulses when there is metal near it. Either way the operation of the ignitor is the same, it detects a small voltage pulse from the pickup and SHORTS/OPENS (controls) the coils to get the spark at the right time.

[rustybronco]

Have you seen this? http://www.mtsac.edu/~cliff/storage/...-ES-L_1983.PDF

pages 15-17...

[spyug]

Thanks guys. I'm still not clear on this with regard to the signal generator pick-ups and the "powering" of the ignitor, however.

The igniter sends a constant signal to the generators which then complete the circuit as the rotor rotates to it.

So does that mean, with the ignition on I can detect voltage on the pinouts where the signal generator plugs in?

Also

The igniter is powered. Since it's isolated from the chassis it has both + and - in.

.This confuses me, where is the power in? It must from the leads to the coils no?

Also I asked in another thread what the green/yellow wire attached to the signal generator plate fixture screw was for. I take its a ground?

I'm getting a better picture of this subsystem and hopefully I'll be able to better diagnose what is or isn't happening.

I appreciate all the help.

cheers,
Spyug

[Billy Ricks]

Thanks guys. I'm still not clear on this with regard to the signal generator pick-ups and the "powering" of the ignitor, however.

So does that mean, with the ignition on I can detect voltage on the pinouts where the signal generator plugs in?

Also
.This confuses me, where is the power in? It must from the leads to the coils no?

Also I asked in another thread what the green/yellow wire attached to the signal generator plate fixture screw was for. I take its a ground?

I'm getting a better picture of this subsystem and hopefully I'll be able to better diagnose what is or isn't happening.

I appreciate all the help.

cheers,
Spyug

On the igniter, were talking '83 750 right? Yours should be the same as mine. The left plug is signal to the coils and positive and negative in and one wire out to each coil. On the right plug you have two wires that run one each to the two signal generators and two back into the igniter, one back from each generator. The rotor trips the generator and cues the igniter to fire.

[rustybronco]

Looking at the wiring diagram, the O/W wire sends power to both coils and supplies power to the ignitor via the same O/W wire.

The igniter is powered. Since it's isolated from the chassis it has both + and - in.

Most likely the housing of the ignitor is not electrically connected to any of the ignitors internal circuitry and therefore a separate connection for ground is needed. the ground connection for the ignitor is provided via the B/W wire.

the W and The B/Y wires connected to the coils are grounded by the ignitor. when the coils are grounded the coils build up a magnetic field. when the the coils primary winding(s) are un-grounded by the ignitor, the magnetic field in the coil collapses and induces a voltage across the secondary winding of the coil(s). this is when a similar type of spark occurs that Jim talks about in His 'Sparks and magic' class.

the pickup coil(s) output waveform is used by the ignitor to produce the dwell time needed by the coils, ignition timing and spark advance.

[spyug]

Thanks guys its coming clearer now. I'm planning on diving in deeper tonight in hopes of finding spark.

I was hoping to find someway to measure that I am actually getting a signal from the signal generator to the igniter as I am not sure that I am, even though the pick up coil leads spec out for continuity. I guess that if I am able to trigger a spark by applying the ohmmeter probes to the pinouts for the pick up coils in the igniter then I might infer that I'm not getting a signal from the pick-ups?

As I know the igniter works since it was tested in my 750 and the coils have power and spec out for resistance I'm left thinking the signal generator is not functioning correctly or the signal is just too weak to trigger the igniter.

I'll see what I can come up with this evening but if there are any other hints or suggestions I'd be interested in hearing.

Cheers all,
Spyug

[rustybronco]

I was hoping to find someway to measure that I am actually getting a signal from the signal generator to the igniter as I am not sure that I am, even though the pick up coil leads spec out for continuity.

If you didn't live so far, I'd pop on in with my oscilloscope. I go as far as Komoka fairly often.

[Billy Ricks]

You can jump he leads on the igniter to see if you get spark to the plugs. That will confirm the igniter is alright. On basscliff's site my old response on how the service manual says to test the entire ignition system is posted.

[Billy Ricks]

Looking at the wiring diagram, the O/W wire sends power to both coils and supplies power to the ignitor via the same O/W wire.

Most likely the housing of the ignitor is not electrically connected to any of the ignitors internal circuitry and therefore a separate connection for ground is needed. the ground connection for the ignitor is provided via the B/W wire.

the W and The B/Y wires connected to the coils are grounded by the ignitor. when the coils are grounded the coils build up a magnetic field. when the the coils primary winding(s) are un-grounded by the ignitor, the magnetic field in the coil collapses and induces a voltage across the secondary winding of the coil(s). this is when a similar type of spark occurs that Jim talks about in His 'Sparks and magic' class.

the pickup coil(s) output waveform is used by the ignitor to produce the dwell time needed by the coils, ignition timing and spark advance.

I should pay more attention to you EE guys. That's the direction my counselors wanted me to go with the math scores I had. I was young and dumb though.