runs when key is on
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Senior User
Joined: May 2002
Posts: 353
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From: Bayonne NJ
runs when key is on
Hi guys, I have a 1979 f100 with a 302. I just swapped intakes and carbs thinking i had a carb problem. Unfortunately, now i can't get this thing started up. When i turn on the truck the truck starts and kinda runs until I let go of the key, at which time it stops. I was reading on here that it could be a bad ignition module so I started checking it out with a mulitimeter. At the ignition side I got 12V on the other side i got pretty much nothing. So I bought a new Module. I got home and hooked it up and i am getting the same problem. Weird thing to me is I am getting 5 volts to the coil. I know this can't be right? Where do I go from here?
Thanks guys
Thanks guys
Posting Guru
Joined: Jun 1999
Posts: 2,415
Likes: 3
From: Comox Valley, Canada
Sounds like you are missing the voltage to the coil in the run position or to the module. Guess it is time to start some voltage checks.
White and red wire to module should have 12 volts to them when key is in start for white and run for red.
Coil should have 12 volts to it when key is in start and 8-9 when key is in run.
Quick check for module is to jump 12 volts to the coil + and start the truck.....if it starts and runs the ignition system, coil, module sparkplugs dizzy wiring are good. The problem is the resistor wire circuit.
If it doesnt run, and you have a known good module, could be the igntion switch or the wiring to the module.
White and red wire to module should have 12 volts to them when key is in start for white and run for red.
Coil should have 12 volts to it when key is in start and 8-9 when key is in run.
Quick check for module is to jump 12 volts to the coil + and start the truck.....if it starts and runs the ignition system, coil, module sparkplugs dizzy wiring are good. The problem is the resistor wire circuit.
If it doesnt run, and you have a known good module, could be the igntion switch or the wiring to the module.
Thread Starter
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Senior User
Joined: May 2002
Posts: 353
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From: Bayonne NJ
Thanks for the reply. I have 12V at the ignition. But on the other side of the module, I have nothing. Also, i know this sounds stupid but do I unhook the wires on the coil and run them straight from the batt.?
Thanks
Thanks
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Joined: Jan 2001
Posts: 57,025
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From: Virginia
Sounds like you may have missed hooking a wire up. If you put the ignition switch in run, and put one meter lead on ground, and the other on the coil positive, do you get 12 volts(all the time, not just in start mode).
If you only get 12 volts in start, and not in run, sounds like you may have the (red/green I think) from the firewall loose.
If you want to do a temporary test, take ONE wire from the battery positive, to the coil positive, and see if it will run. Leave the original negative coil wire installed during this test(it goes to the module). Don't run it like this long term, because you need the resistor in the circuit like the above duraspark link showed.
If you only get 12 volts in start, and not in run, sounds like you may have the (red/green I think) from the firewall loose.
If you want to do a temporary test, take ONE wire from the battery positive, to the coil positive, and see if it will run. Leave the original negative coil wire installed during this test(it goes to the module). Don't run it like this long term, because you need the resistor in the circuit like the above duraspark link showed.
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