i have a 73 crew cab 4x4 with 300 six. when i turn the engine over it will start but as soon as the key goes over to the run position it sputters and dies. it's not a fuel issue because when i kept the starter engaged for about 20 seconds the engine ran and reved up fine.
i pulled the key switch and plugged in a new one, same problem. i think it must be somewhere in my wireing or distributer. i have a davis unified ignition that is only a couple of years old. any thoughts fellas, am i on the right path??

 

Turn your switch to the run position and test if you have voltage at the coil, if you don't then it has to be the wiring or the switch. Do you now have electronic ignition, if it's anything like ford's duraspark I or II then it could very well be the control module.

 

Twenty dollars says it's the ballast resistor. I'm not sure on that model, the resistor may be a little white rectangular box about three inches long on the inner guard or firewall , or it may be a thick black wire from the coil with I think a yellow stripe.
When the key is in 'start', it puts 12 volts to the coil. When it goes back to 'run' the coil only needs 8 volts, so the current is routed through the ballast resistor. You can bodge it up by putting 12 volts to the coil in 'run', but your coil won't last very long.

 

I agree with CSEASTAUGH, it sounds like a ballast resistor, or a bad ign switch. Ballast resistors are used on older trucks and cars that have a breaker point type distributor system.

The purpose of the resister is to reduce the current flowing through the breaker points while the engine is running. Reducing this current reduces breaker point contact arcing, allowing the points to last longer. This reduction in current flow also causes a corresponding decrease in coil output voltage, which goes unnoticed since there is still plenty of voltage to jump the gap in the spark plugs.

When starting, most of the battery’s current flows to the starter, creating an additional voltage drop at the coil. If the ballast resister was still in the circuit, the output voltage of the coil would be extreme low and insufficient to start the vehicle. Therefore, the resister is bypassed during starting.

If you want to be certain that it is the resister and not the ign switch, you can jumper out the resistor. If the resistor is bad, the engine should start and continue to run. If you perform this test, make sure you don’t run the engine too long or else you may have to replace the points as well.

Please write back and let us know what you find.
John24255

 

thanks, i'll check the resistor. is that thick black wire your talking about go all the way boack to the ignition key switch. i can't rember seeing a white resistor but i will look. i had to have the truck towed out to the shop at our farm so i won't be by a computer until this evening, but i will post when i get back.

 

thanks fellas, we made short work of that one. i traced the big black wire with the yellow stripe and instead of a resistor there was a fuse. when the guy put in the davis unified ignition he replaced the resistor with a fuse. so a five cent part cost me alot of money.

here is a new problem though. my altinator has been surging for a while now. i decided to get a new one so i didn't blow any more fuses. i replaced the alternator, alt. belt, voltage regulator, and even the starter solenoid (because i replaced the starter about two months ago. the new problem is my choke coming on. i start my truck and when it goes to high idle i stomp on the gas and it kicks down to low idle. then when i'm driving down the road and slow down or push on the clutch it stays at high idle until i stomp on the gas again. it gets very frustrating in town, stop light to stop light. any thoughts???
Thanks.

 

The reason it fires when you turn it to start, is there is a wire hooked directly to the Solenoid that gives the coil a true 12 volts during cranking. This is to compensate for the draw the starter takes away and give a better spark to start the cold engine. You are not getting voltage to the coil in the Run position for some reason.