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Re: [T3] When electronic points die they can still kinda work.

On 14 Aug 2006 at 9:49, Toby -- '72 Squareback wrote:

> What *completely baffled* me was that the engine would run fine as long as
> the gas pedal was pressed, even if by the slightest amount.  Anyway, just
> another bit of something to throw into people's knowledge bucket.

After thinking about this for a couple days, I think I have an explanation.

The Pertronics rides on the breaker plate, the same as the points did. The 
vacuum advance works by rotating this plate to change the relationship between 
the pickup and the cam. When the Pertronics moves with the plate, the 2 wires 
leading to it have to move also, so they need some extra length in there for 
the wire to flex.

I suspect that after a few years of flexing, one of your wires finally broke 
inside the insulation. Of course this shut down your ignition, but when you 
moved the gas pedal, you changed the vacuum conditions on the vacuum advance, 
moving the breaker plate just a little bit. This probably flexed the wire again 
in a way which renewed the contact and allowed the ignition to kick in again. 
When this happened, the raw fuel from the previous unsparked strokes was 
ignited in the exhaust system, creating the backfire.  

Alternatively, the wire may not have broken, instead, the coil wire could have 
abraded against something, worn thru the insulation,and shorted to ground. 
Moving the breaker plate could have removed the short.

Either way, the fault is most likely with the wiring rather than the Pertronics 
innards themselves.

The good news is that this means the Pertronics is probably fixable, but you 
will want to repair the wire and route it to allow gentle flex, minimizing the 
chance of this happening again.

You can find the break by just pulling on the wire and seeing where it 

I thought of this because this once happened to me with a set of standard 
points. I have a number of CDI ignitions which I use with standard points. One 
of the advantages of the CDI systems is that the points themselves last 
forever, but the WIRES don't! I had one of those internal wire breaks many  
years ago, and it had these same symptoms.

One of the advantages of the Bosch points system our cars use is that you get a 
new wire with each set of points. I've known people with other kinds of cars 
where that little wire is part of the distributor and does not get changed. A 
break there is more likely to eventually happen and harder to fix when it does.

Jim Adney
Madison, WI 53711-3054

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