Timing lights and coil on plug

[sparkybean]

Im trying to figure out a way to use my shiney new timing light with a coil on plug engine. Its an astra X engine, with a 'coil rail' as it were over all of the spark plugs, so there is no HT lead to connect the timing light pickup to without disconnecting the coil(s?) from the spark plugs. And then of course the engine wont run.

Like this:



The only way i can think to get around this is to pull the coil out, make 4 small h leads and connect them from each spark plug to each coil output. Surely this isnt common practice? Any easier ways of doing this?

Thanks.

Edited by sparkybean on Thursday 7th October 20:35

[stevieturbo]

It's a rarity you would need to use a timing light on a modern engine, as you have no way of adjusting timing.

[sparkybean]

So how would i check timing, even knowing i couldnt adjust it?

Edited by sparkybean on Thursday 7th October 21:43

[anonymous-user]

I took my timming light apart, identified where the HT "trigger" entered the uC in the light, with a suitable resistor connected this trigger directly to the "low voltage" trigger wire on one of my coil packs

(normally, inductive pick up lights, use a coil that sits around a ferrite core (that you can open and "snap" around an HT lead) this coil therefore has a voltage induced in it by the HT lead when it fires. This voltage is used as an "Interupt" sense on the microcontroller that runs the timing lamp. When this IrQ is fired, the stobe lamp is fired. By connecting the Irq line direct to the coil pack LT trigger wire you basically just avoid the HT bit of the circuit.)

[stevieturbo]

Max_Torque said:

I took my timming light apart, identified where the HT "trigger" entered the uC in the light, with a suitable resistor connected this trigger directly to the "low voltage" trigger wire on one of my coil packs

(normally, inductive pick up lights, use a coil that sits around a ferrite core (that you can open and "snap" around an HT lead) this coil therefore has a voltage induced in it by the HT lead when it fires. This voltage is used as an "Interupt" sense on the microcontroller that runs the timing lamp. When this IrQ is fired, the stobe lamp is fired. By connecting the Irq line direct to the coil pack LT trigger wire you basically just avoid the HT bit of the circuit.)

And would that work on coils with built in ignitors ?


Mocking up 4 short leads and doing it that way is easy enough. The most important thing is insulation, making sure it cannot arc anywhere. Especially onto yourself lol

[anonymous-user]

stevieturbo said:

And would that work on coils with built in ignitors ?

sure, it's just a question of getting the series resistance correct so that the "on" voltage is enough to saturate the opto-isolator (or pulse transformer) in the lamp. (i.e. coils with built in drivers can be triggered by 5v or 12v depending on ems system. So you need to arrange the resistance to get enough current to load the lamps isolation system

[sparkybean]

Max_Torque said:

stevieturbo said:

And would that work on coils with built in ignitors ?

sure, it's just a question of getting the series resistance correct so that the "on" voltage is enough to saturate the opto-isolator (or pulse transformer) in the lamp. (i.e. coils with built in drivers can be triggered by 5v or 12v depending on ems system. So you need to arrange the resistance to get enough current to load the lamps isolation system

Its an option, but pulling apart the timing light would be a project in itself. Ill have to get hold of an old one to try it on first...

Edited by sparkybean on Monday 11th October 11:43

[buggalugs]

Max_Torque said:

stevieturbo said:

And would that work on coils with built in ignitors ?

sure, it's just a question of getting the series resistance correct so that the "on" voltage is enough to saturate the opto-isolator (or pulse transformer) in the lamp. (i.e. coils with built in drivers can be triggered by 5v or 12v depending on ems system. So you need to arrange the resistance to get enough current to load the lamps isolation system

Forgive me but was just thinking about this, wouldn't you be triggering on the wrong edge of the signal? Dwell would be involved as well which is neither known or constant.

[Mr2Mike]

buggalugs said:

Forgive me but was just thinking about this, wouldn't you be triggering on the wrong edge of the signal? Dwell would be involved as well which is neither known or constant.

Dwell period on a modern ignition system is almost constant - it varies a small amount with the system voltage but that's it. The problem is a fixed dwell period obviously translates into a variable angle at different RPM. Ideally you need to trigger on the high voltage transient (200-300v) on the coil primary which occurs immediately prior to the plug firing.

[buggalugs]

Mr2Mike said:

buggalugs said:

Forgive me but was just thinking about this, wouldn't you be triggering on the wrong edge of the signal? Dwell would be involved as well which is neither known or constant.

Dwell period on a modern ignition system is almost constant - it varies a small amount with the system voltage but that's it. The problem is a fixed dwell period obviously translates into a variable angle at different RPM. Ideally you need to trigger on the high voltage transient (200-300v) on the coil primary which occurs immediately prior to the plug firing.

So triggering on the low voltage turn on would give you a reading of quite a bit more advance than you were really getting, with the overread getting linearly worse at higher revs.

I wonder if the thing to do is take the pickup apart and bodge it to go round the neck of the coil in situ...

[anonymous-user]

Well it depends where you tap into the sensing circuit. on my timing lamp the induction coil is used to trigger an optoisolator, the output of which is pulled high with a 10k resistor to vcc. When the inductive coil is triggered by the spark energy in the plug lead, it triggers the opto, which pulls the IO line on the micro low, and triggers an interupt. What i did was to couple the coil low tension trigger wire directly to the interupt line (with a suitable voltage divider (series R & pull down R). So, when the coil starts to charge the line is pulled high, then when the trigger line goes low (and fires the coil) the interupt line is also pulled low. The only delay in this case is the coil amplifer latency (<50us so no issue)

[anonymous-user]

buggalugs said:

Mr2Mike said:

buggalugs said:

I wonder if the thing to do is take the pickup apart and bodge it to go round the neck of the coil in situ...

I would immagine that wrapping a few turns of wire around the "boot" section of the coil pack would probably work if you connected these turns to the original pickup wires

[buggalugs]

Max_Torque said:

Well it depends where you tap into the sensing circuit. on my timing lamp the induction coil is used to trigger an optoisolator, the output of which is pulled high with a 10k resistor to vcc. When the inductive coil is triggered by the spark energy in the plug lead, it triggers the opto, which pulls the IO line on the micro low, and triggers an interupt. What i did was to couple the coil low tension trigger wire directly to the interupt line (with a suitable voltage divider (series R & pull down R). So, when the coil starts to charge the line is pulled high, then when the trigger line goes low (and fires the coil) the interupt line is also pulled low. The only delay in this case is the coil amplifer latency (<50us so no issue)

Just checking