car starts but shuts off when key is released to run position

[Contibob]

Hello, My car has been in the upholstery shop and it won't keep running. I put a pertronix on it about 3 months ago and it has been running better than ever. Took it to the shop and it started perfectly until two days ago. It starts immediately then when key is released to run it shuts off immediately. After trying it a few times it will start and run. Sounds like ignition switch to me, what are your ideas. As far as I know it has the original ignition switch. By the way car is stock 312 4bl with only modification being the pertronix. Bob

[BWhitmore]

If the Pertronix was installed with a ballast resistor, I would suspect that the resistor is faulty.  The resistor is designed to deliver a full 12 volts to the coil when the engine is being cranked; when the key is released to the run position the voltage is reduced to 9 volts going to the coil.  If the resistor has failed you get 12 volts to the coil while cranking, but 0 volts to the coil when the key is released to the run position, thus the engine will shut off. 

[Contibob]

Per pertronix instruction, it was installed without the ballast resistor because I used their coil which has an internal resistor.

[oldave57]

Bob,
The original wiring harness has a brown wire which connected to the + terminal of the coil and a red wire that connected to the resistor.  Both of these wires should now be connected to the + terminal of the new Pertronix coil.  The brown wire comes from the starter solenoid and provided power to the original coil during cranking to by-pass the reduced voltage to the coil from the resistor.  The red wire comes from the ignition switch, but power is shut off to the red wire when the switch is in the crank position. 

The Pertronix coil should have 3 wires connected to the + terminal (the brown and red wires from the original harness plus the red wire from the Pertronix igniter in the distributor).  The black wire from the Pertronix igniter goes to the negative terminal on the Pertronix coil. 

If you have only the brown wire connected to the coil, it is likely that the coil is only getting power during cranking and not during the regular "on" position of the ignition switch.

Good luck with your installation.  It can be frustrating when it doesn't work but the Pertronix has worked great on my car for the last 3 years or so with no problems.

Regards,
Dave

[RICH MUISE]

If I'm reading Bob correctly, the car ran fine for a few months, then something happened so it is no longer working. To me that indicates he had it set up correctly, but  something in the system went bad...wire, coil, internal resistor, etc....

[hiball3985]

Turn the key to the on position and check the voltage at the coil, If there is no power it could be in the wire from the ignition switch or the switch.

[Contibob]

yes the car was running well. The shop has started and shut off the car many times to move it around and now all of a sudden it won't stay running. ?

[oldave57]

I think the suggestion of checking for power at the coil with the key in the run position is an excellent way to check to see if the circuit has power in the run position.  If the key is bad, the other things that are powered with the key "on" should not work (gauges, radio, etc) so if they work, the problem is more likely to be in the line between the key and the coil.

Another potential problem might be that the shop could have left the key in the "run" position for an extended time with the engine stopped and this can cause damage to the Pertronix Igniter I system, which could be a cause of failure.  The later Pertronix systems have protection against this failure (I still have the Igniter I with no problems, but I try to remember not to leave the key in the on position for this reason)

[Lou]

Check the wires on the starter relay on the inner fender,sounds like the run wire has fallen off or has a break in it. With the key off, you can use a jumper from the hot side to the start terminal, once started, touch jumper to the run terminal.

[BWhitmore]

Call Pertronix, they have an excellent Help Line.

[canadian_ranchero]

get a volt meter and do some tests

[Contibob]

Thank you for all your suggestions. I'll give them a try. Bob