Starts & dies, starts & dies, starts & dies...

[alfan]

My 74 Spider was running fine, then suddenly...starts and dies, starts and dies after running for only a few seconds. Someone suggested it could be a faulty ballast resistor, but there is none on the ignition coil. Then, someone suggested that there IS a ballast resistor, but it is somewhere under the dash -- but who knows where it is? Any ideas on this one?

[Tifosi]

I could be off in my assessment, but I always thought the ballast was to help starting, not running.

Based on that, the ballast is most likely OK (engine starts) but something else is preventing it from continuing to run. (prolly not the coil, as it does indeed start and run for a short period thus it's likely functioning to an adiquate degree)

Wait for someone smarter to reply for sure, but IMO, you're likely barking up the wrong tree at this point.

My guess would be something fuel related, though a cracked/damaged dizzy cap or rotor wouldn't be out of the question, nor would a recently fouled plug or two. (heck, could be a lotta things actually, but I don't think a ballast resistor is it)

[conedriver]

Does it actually run for a few seconds, or just chug a little and act like it's just about to start. If the latter, try changing the condensor (inside the distributor with the ignition points).

Quote:

Originally Posted by alfan My 74 Spider was running fine, then suddenly...starts and dies, starts and dies after running for only a few seconds. Someone suggested it could be a faulty ballast resistor, but there is none on the ignition coil. Then, someone suggested that there IS a ballast resistor, but it is somewhere under the dash -- but who knows where it is? Any ideas on this one?

[papajam]

Easy way to check for a bad ballast resistor, whether it's in the stock location on the coil or not, is to turn on the ignition and check voltage at the positive terminal (#15) on the ignition coil. If at or near battery voltage, there's either no resistor in the circuit or the resistor is good. If no voltage, there's either a fault in the coil power feed circuit (possible ignition switch) or a bad ballast resistor.
Another possibility for a start/stop condition is a stuck closed microswitch on the Spica injection pump. To test, disconnect and insulate the wire at the Fuel Cutoff Solenoid (FCS). Of the two solenoids on the Spica pump, it is the solenoid closer toward the front of the car. If the engine now starts and runs, the microswitch is at fault.

[Andrew]

Spica or carbs? Fuel supply?
Was just talking to a guy last night who had this symptom on a car with clogged exhaust, complete with spitting back through the carbs.
Andrew

[Alfacliff]

the ballast resistor cuts down the current to the coil when the engine is running. the start circuit jumpes the ballast while the starter is running, this is to increase the voltage to the coil when cranking and then reduce the current thru the coil when the engine is running.
thats why a bad ballast or wireing to the coil will cause this engine only runs when cranking problem.

[Roadtrip]

What Jim said. A shorted fuel cutoff solenoid microswitch will cause that problem. When the key switch is in "Start," the microswitch circuit is not energized, however, after the engine fires and you release the key switch back to "Run," the circuit is re-energized, the current runs through the shorted microswitch regardless of command, the fuel cutoff solenoid is activated and the engine stops.

[alfan]

Thanks a lot, guys, for your helpful posts. Problem solved! The ignition coil tested OK, and the ballast resistor presumably good. Removal of the wire at the fuel cutoff solenoid resulted in an instant start, so must have been the injection pump microswitch. I understand that the microswitch is in a pretty tough location to replace, so I guess for now I will put up with the pop-pop-pop when releasing the gas pedal.

My lesson in this one was to learn that this rather odd problem could have two equally possible causes.