The Mysterious Start/No-Start
Dabney Dufus worked on a problem with one of his 253 old cars, a 1960 Ford Falcon, for almost two days. The engine spins over in the "start" mode and actually runs, but when he returns the ignition key to the "run" position the car shuts off.
Dabney tried replacing the ignition switch...no go. Then he replaced the starter... nada. "Ok," Dabney said, "so that's the way it's going to be, eh? I'll show you!" He wheeled his toolbox up to the side of the car and started ripping out parts left and right. He replaced the points, condenser, rotor, cap and wires ...he replaced everything but the headlights...still no luck. Dabney didn't want to admit it, but he was whipped. He hated to do it but he had to call the Doctor...
That's Doctor Crankshaft. We call him 'Doc' around here, or sometimes just 'Crank'. Doc's been a fixture at the Second Chance Garage longer than anyone can remember. His dad started the shop back in 1933. And when we took over the place, it was part of the deal that Doc could have his office in the back room. But as cantankerous as he is, he's not bad to have around, 'cause he has a lot of history with old cars.
"Dabney, my boy" Doctor Crankshaft screamed into the phone. One of the things that Dabney dislikes about the Doctor is that he shouts into the phone. "Watcha got workin'?" (Doc's usual salutation).
"My '60 Falcon is driving me crazy, Doc. I've tried everything I know how and a few I don't, and it still won't run." He explained all the steps he'd taken to try to fix the problem.
"Well, bust my knuckles, my boy! You overlooked the most obvious thing." The Doctor respects Dabney, although he's not convinced Dabney is the sharpest tool in the drawer.
"And you must have dumped a ton of money on this one...and it still doesn't work, heh heh?" The Doctor doesn't even try to conceal his amusement. "Well, here's something for you to chew on, Dabney, my boy. Your problem is the ignition resistor. Yeah, Dabney, that's right...the ignition resistor. In these old Falcons, you want to look at the resistor wire that runs from the switch to the coil. You young pups think you know everything about old ignition systems and then go off half-cocked swapping out a whole bunch of parts that aren't causing the problem."
Dabney could feel his face turning red. The Doctor has a way of making Dabney feel embarrassed?even over the phone.
"You see, boy," the Doctor continued, "an ignition coil is designed to provide enough high voltage to run the engine at its maximum rpm, using full battery voltage. But, if it were allowed to run at full battery voltage at idle or slow speeds it would heat up and fail. So those smart engineers back then added a resistor to the circuit leading to the coil. That's in the "run" position on the ignition switch. And they did this to lower the battery voltage, maybe as low as 7 volts in some 12-volt systems. In your Falcon that resistor is a resistance wire. But in other cars it could be a wire-wound resistor mounted in the engine bay or a special coil with an internal resistor.
"I'm not sure I get it," Dabney said, hoping that the Doctor would take it easy on him this time.
"So why did the engine run in the 'start' position?"
"It's simple, my boy. A cold engine needs all the spark it can get to start. And those engineers designed the "start" mode to provide full battery voltage by using separate wiring, a relay or some other means. That's why your engine runs in the "start" position but not in the "run" position. Replace the resistor wire and she'll purr along just fine."
"I think I get it now. Thanks Doc." Dabney was obviously in a hurry to get back to his Falcon to test out his new-found knowledge.
Just about lunchtime, as the Doctor was closing up his backroom office (Doc doesn't work full days anymore), Dabney pulls up in his Falcon. "You're right, Doc, it purrs like a kitten. I just wanted to thank you again for the help, but I gotta run."
"What's your hurry, my boy," asked Doc.
"I think I've found a buyer for all those parts I took out, and I want to get to him before he changes his mind."
"Heh, heh," Doc chuckled to himself, shaking his head as he walked away.