Re: Naive twin spark question

[Roe Willo-C14902 <Willo_Roe-C14902@domain.elided>]

I haven't seen the correct answer to this one yet so here goes:

Andrew asked:
When does the twin spark fire?

I believe that Andrew is asking about the newer design engines without
distributors. The sparkplugs on these engines fire both on the power and
exhaust stroke. There are 2 coil packs, each pack contains two coils and is
connected to 4 spark plugs one pack is for the 'large' plugs and the other
for the smaller ones. One coil in each pack gives sparks to cylinders 1 and
4 and the other generates sparks in cylinders 2 and 3. 

The signal from the ecu causes the coil packs to send sparks to cylinder 1
during its power stroke. The sparks in the large and small plugs are
seperated slightly to control the flame in the cylinder, which is what twin
sparks are all about. HOWEVER, because the sparkplugs for cylinder 4 are
also connected to the coils used for cylinder 1 they also fire at the same
time which just so happens to be the top of the exhaust stroke. These are
waste sparks, they have no function in emission control or power generation.


I know this sounds confusing, but if you draw it out you will see it is very
simple and eliminates the use of 2 distributors and a lot of high tension
leads that were used in the earlier twinsparks.

A very clear explanation is given in 'The Sparky Bits' by Tony Goadby in the
Alfa Romeo Owners Club Magazine Vol32 No2 (April 1998).

Willo Roe
Dublin, Ireland
'69 Wolseley Hornet
'84 Alfetta GTV TS
'89 Alfa 75 TS

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