712M won't start. Looking for ideas.

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rmel
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Re: 712M won't start. Looking for ideas.

Post by rmel »

Hmmm, OK, so I think what your saying is that after you performed
EI's Ignitor test rotating the engine until the Black lead indicated 24V,
you then touched that lead to the negative coil terminal and it dropped
to 12V. Well that's mighty odd, as at that point the Ignitor is OFF and
there should be no path for current flow through the coil or Ballast resistor.

Do you have the Ignitor Red lead connected to the positve side of the coil
or direct to a 24V source.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712MK

Driver: Ron // KO0Q
cc rider
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Re: 712M won't start. Looking for ideas.

Post by cc rider »

It was directly to the 24V source wire. Yes it is very odd and frankly confusing as heck to me. Tried it with both old and new coils and the results are the same.
Perhaps there is a scenario whereby the Ignitor can pass the Hall effect test but still fail at the negative coil terminal connection, but I don't have enough electro-smarts to figure it through.
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rmel
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Re: 712M won't start. Looking for ideas.

Post by rmel »

OK, so... the Ignitor is powered direct from the Battery and NOT via the Ballast resistor.

A long shot as I suspect you measured this long ago but what is the measured voltage
on the positive terminal of the Coil when the Black wire is NOT connected. It should be
the Battery voltage, if it happens to be 12V then my bet would be the RPM limiter has
failed and may be dropping the voltage to the coil. Yes, I know you shorted the two
mid point terminals on the limiter but it still has internal connections and it does have
a ground connection.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712MK

Driver: Ron // KO0Q
cc rider
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Re: 712M won't start. Looking for ideas.

Post by cc rider »

Yes the measured voltage from the positive terminal to ground is 24V, also when I connect to the black wire coming off the Pertronix ignitor. The instant I connect the black wire to the negative coil terminal it instantly drops to about 12 volts.

Also I measured the ballast resistor and got 4.5 ohms, just like RPinAZ got. So I assume it is good.

I think I have covered just about all bases: Coil, distributor cap, plugs, voltage regulator, ballast resistor, by-passing the 4500 rpm limiter...

Does this leave the Pertronix as the culprit despite passing the test on the Hall effect?
cc rider
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Re: 712M won't start. Looking for ideas.

Post by cc rider »

If it truly is the RPM limiter that is the culprit, is the remedy to just remove it? I've already bypassed it so it serves no further function?
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rmel
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Re: 712M won't start. Looking for ideas.

Post by rmel »

I’d recommend making the voltage measurement first.
If you see 12v W/O the Ignitor connected then something
is wrong with the power delivery to the coil. As far as the
RPM limiter goes, if you removed the connector and bypassed
the pins on the connector and left it hanging then it's not
going to effect anything. But if you jumpered the connector
from the wire side and left it in place -- connected, then
remove the connector.

You don't have to remove the unit it if not connected.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712MK

Driver: Ron // KO0Q
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rmel
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Re: 712M won't start. Looking for ideas.

Post by rmel »

Oh! I missed seeing your earlier posting with your measurements -- sorry bout that.

Soo....you do have 24V at the coil positive terminal and the Ballast is 4.5 Ohms.
It sure does look like all things are reasonable from that perspective.

It remains very odd that when you connect the control wire from the Pertronix to
the coil it drops to 12V but with the Ignotor supposedly OFF e.g. Engine was rotated to TDC.

But wait :shock: With the 12V on the Neg terminal and if I understood correctly 24V on the
Positive terminal at the same time -- you would have nearly 4 Amps through the coil which
can't happen unless the Ballast resistor was bypassed to Battery. Even at that, 12V on the Negative
terminal is goofy. In a static situation (engine off) it should be about about 0.5V with Ignitor ON
(at TDC) and about 24V Ignitor OFF (Hall between lobes). I suppose it would be worth cranking
the engine with the Hall between lobes so the Ignitor is ON at least to see if it actually turns on.

Something just does not seem right here :oops: or I am not understating the situation correctly.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712MK

Driver: Ron // KO0Q
cc rider
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Re: 712M won't start. Looking for ideas.

Post by cc rider »

Yes well the situation is mighty confusing. I think I will order an old-school points and condenser from SAV to at least get the thing moving again. Only $20 and if it turns out the Ignitor was the culprit I can order a new one and keep the old points & condenser as backup if we ever get an EMP event what with nuclear war being talked about for the first time in decades. Will keep everyone posted.
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Re: 712M won't start. Looking for ideas.

Post by pinzinator »

Did you ever discover what the problem was?
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