Major Service Woe or Two

[Andy B]

.....
And some use a single coil to drive two plugs per cylinder with two leads. Because they could.

That's what the Smart Roadster uses

[Marks DTM Calib]

As for DIS and Coil pack, the DIS was a module which utilised wasted spark tech to replace a distributor but, still had traditional HT leads.

Then came the 'coil per plug' or 'coil on plug' as it was sometimes called, directly connecting the coil to the plug with no external wires, some manufacturers combined mulitiple coil on plugs into a single 'coil pack'.

And some use a single coil to drive two plugs per cylinder with two leads. Because they could.

Thats simply an extension of the wasted spark DIS system, with a lead connected to each end of the secondary winding, but with more turns to get the volts up and a bit more iron to store some extra energy (which may not be good for reliability) 

[Marks DTM Calib]

.....
And some use a single coil to drive two plugs per cylinder with two leads. Because they could.

That's what the Smart Roadster uses

The Smart one is two coils in one pack 

[Andy B]

.....
And some use a single coil to drive two plugs per cylinder with two leads. Because they could.

That's what the Smart Roadster uses

The Smart one is two coils in one pack 

OK ... there's just one block with 2 HT leads from it 

[Marks DTM Calib]

.....
And some use a single coil to drive two plugs per cylinder with two leads. Because they could.

That's what the Smart Roadster uses

The Smart one is two coils in one pack 

OK ... there's just one block with 2 HT leads from it 

If you look closely you can see the two bulges from each coil



If you fed two plugs off a single coil only one plug would fire most of the time 

[LC0112G]

If you fed two plugs off a single coil only one plug would fire most of the time 

That's not strictly true. As long as there is a circuit from one terminal of the coil back to the other terminal, it'll fire. The second terminal doesn't have to be a chassis/ground potential.

I can name at least one case where the circuit goes coil+ve -> spark plug1 tip - >spark plug1 threads -> cylinder head ->spark plug2 threads -> spark plug2 tip -> coil-ve.

Both spark plugs 1&2 fire every time at the same time. One cylinder is at the top of the exhaust stroke, whilst the other is at the top of the compression stroke. Although the exhaust stroke spark is wasted (hence the term wasted spark), it takes very little energy to fire it when it's surrounded by hot combustion gasses, so the energy loss is minimal.

It makes spark timing simpler - you can do the timing off the crank (rather than the cam) since you don't need to know if the piston is in the compression or exhaust phase of the 4 strokes.

No idea if that's how a Smart car works though.

[Lizzie Zoom]

For when I fit the new DIS pack, is the connector on the old one easy to unclip please?

It's just a tab. Flat blade screwdriver under the tab and wiggle it clear. 

Thanks!

[Lizzie Zoom]

..... 
Usual trouble in getting to spark plug 6, but after much cursing the idiots who designed so much in the way of this plug that I have wasted hours on over the years, I finally extracted it.  .....

Plugs on an Omega & even No 6 plug on a Senator are dead easy compared to my Smart Roadster. 
Rear panels off first
Then all 6 plugs .... top 3 are easy .... lower 3 not so easy

Yes, that does seem far worse than with the Omega, and much, much harder than a Senator which was dead easy!

[Lizzie Zoom]

For when I fit the new DIS pack, is the connector on the old one easy to unclip please?

No wonder the plug change takes so long if you don't unplug it for that.

10" combination of wobble extensions makes short work of plug 6. The only reason it can be a pig is if it has never been changed by previous laziness.

No, I never have, but there again I have only done two major services on the current Omega.

As for changing plug 6;  I always have, but I now realise my mistake of not removing the cable tray on the current car.  I did on the 3.0's I have had, but usually when replacing the cam cover gaskets.  When I did those, I used to change my plugs as part of the major service.  Why I have reverted to not doing that I cannot explain, but perhaps I am tiring of all this car mechanics malarkey at my growing age!

[Andy B]

.....
If you look closely you can see the two bulges from each coil
..... ....

As soon as you said it knew you were right ....  but checked on one of my spare coils 

[Kevin Wood]

If you fed two plugs off a single coil only one plug would fire most of the time 

That's not strictly true. As long as there is a circuit from one terminal of the coil back to the other terminal, it'll fire. The second terminal doesn't have to be a chassis/ground potential.

I can name at least one case where the circuit goes coil+ve -> spark plug1 tip - >spark plug1 threads -> cylinder head ->spark plug2 threads -> spark plug2 tip -> coil-ve.

Both spark plugs 1&2 fire every time at the same time. One cylinder is at the top of the exhaust stroke, whilst the other is at the top of the compression stroke. Although the exhaust stroke spark is wasted (hence the term wasted spark), it takes very little energy to fire it when it's surrounded by hot combustion gasses, so the energy loss is minimal.

It makes spark timing simpler - you can do the timing off the crank (rather than the cam) since you don't need to know if the piston is in the compression or exhaust phase of the 4 strokes.

No idea if that's how a Smart car works though.

What you describe is how a wasted spark coil works. One plug of the pair is always in a cylinder on its exhaust stroke, so it has no compression, and needs a much lower voltage to break down than the one that has full compression pressure on it, hence both plugs fire but most of the energy from the coil goes to the one under compression since it has a much higher voltage across it by the time it fires.

If you connected two in the same cylinder, in parallel, to a coil on a twin spark setup like the Smart, you'd only ever get the "easiest" plug firing since the current would take the path of least resistance, hence you need a pair of coils.

[STEMO]

My first wife only had a single coil in, and she certainly used to fire on all cylinders. Dirty cow, she was. 

She wore out my piston 

[Sir Tigger KC]

My first wife only had a single coil in, and she certainly used to fire on all cylinders. Dirty cow, she was. 

She wore out my piston 

Does that mean you also have a wasted spark Uncle STEMO?     

[Raeturbo]

So you're pissed and broke then my friend?🤣

[Raeturbo]

May be a gummed up ring😂😂🤣