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On Fri, 2005-10-28 at 06:40, Matthew Jones wrote:
> > From: J. Jonik
> > * What performance effects if dist. plug wires are in
> > wrong spot ...
>
> I've been thinking about this and trying to work out what the
> effect would be:
>
> The FI points connect the outside 2 wires to the central wire.
> When the cam comes round, it breaks one connection, then the other.
> One outside wire triggers one pair of injectors. The other outside
> wire triggers the other pair.
>
> If the 2 outside wires are swapped, it will simply trigger the
> injectors at the wrong point in the cycle. The fuel will sit in
> the inlet port until the valve opens later. This won't affect
> performance much, if at all.
>
> If the centre wire is swapped with one of the outside wires, only
> 1 pair of injectors will be triggered properly. But what would
> happen to the other trigger? ...
>
> For the sake of explanation, lets say that this arrangement has
> a "good" side (centre wire 'C' on one side, one trigger wire 'X'
> in the centre); and a "bad" side ('X' in the centre, and the other
> trigger wire, 'Y', on the other side).
>
> In this situation, if both points are closed, all 3 wires are
> still connected together. If the "bad" side opens on its own,
> the ECU still sees an open circuit from 'C' to 'Y', so it would
> still trigger 1 set of injectors.
>
> If the "good" side opens on its own, C & X go open circuit,
> triggering one set of injectors. But X and Y would still be
> connected together, so the ECU would also see Y disconnecting
> from C at the same time, i.e. Y has also just gone open circuit,
> and then trigger the other set at the same time.
>
> So, depending on what order the points open, and whether both
> are ever open together, you would either get all injectors firing,
> but with odd fuel timing; or you would get one side firing twice,
> leading to very rich running, possibly even flooding / hard to
> start. But I *think* you would never get only 1/2 the injectors
> firing.
>
> Did anyone stay with me through that?! Its really hard to explain
> without a diagram or hand waving. Have I got this right?
>
> I know the reality is more complex, as it depends on the electronics
> at the ECU end of the wires, whether the common wire is 0, 12V or
> whatever, pull ups, loads etc. etc.
>
Good explaination Matt, but I want to also add one thing about the
trigger points that most people don't think about. The trigger points
opening and closing are what keeps the fuel pump running. Each time one
or other of the points closes, the pump runs for it's "1 second" Do this
fast enough, like on a running engine, and the pump never shuts off.
If one set of points is not functional, and the engine stops with that
set of points closed, the pump won't run at all to get the pressure
primed, and will make the engine hard to start.
--
Russ Wolfe
'71 FB AT
'66 FB MT
'64 T34 (not running)
'65 T1 (not running)
'05 KIA Sorento SUV
russw@classicvw.org
http://www.classicvw.org
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