Idling rough and won't run 250 4.1L.

I think I broke something. So I have a MSD ignition coil hooked up but for some reason I'm firing sporadically after it initially starts. When I hit the start position with the key, she fires up and runs smoothly for a few seconds. Then she starts to fail and the idle gets very rough. She runs enough to stay idling but not enough to even drive. I put a test light on a few of the sparkplugs and sure enough, it's not rhythmic. Could this be the distributor?

Also, a quick question about the starter solenoid. What is the purpose of the "I" post if it's just basically a bridge from the ignition switch to the positive post of the ignition coil?

Also, is it possible to just run 12volts to the coil or do I need a ballast resistor?

You should bw running 12v to the coil. If its less it aint gonna work right. If its not, fix that first.

You can:
A, cut the red wire at the ignition switch and make sure you get it close to the ignition, as theres a black buldge thing that i think is the resistor. Then run 12 gauge wire from the leftover part on the ignition switch and run it to the coil. (I did it this way)

B, theres some way to run it off the battery with a relay or something like that to the coil. (I have no experience with this). Someone here will help you out with this method.

Good luck,
Ryan

Test your voltage an MSD ignition needs full 12 volts. As to the I terminal on Sol. that was was used with the stock Ford ignitions to supply 12 volts to coil (only during starting) you would disconnect it when using an MSD box. Good luck

Well, I tested and tested and tested and I'm definitely getting over 12 volts to my coil but I'm still sputtering and barely idling and according to the timing light I'm not firing evenly. Is it safe to assume I either fried my coil or there is something wrong in the distributor?

If you think that it is the ignition it is probably the carb, fuel...If you think that it is the carb, fuel it is probably the ignition.

drag-200stang":2lqnd2e9 said:

If you think that it is the ignition it is probably the carb, fuel...If you think that it is the carb, fuel it is probably the ignition.

Click to expand...

I hear that! But unfortunately, it's a brand new carb and almost new fuel pump and it was running fine until I started messing with the ignition wiring.

Needed a ballast resistor. $7 at pep boys. Can't run 12 volts directly to the coil from the battery cause it over heats and also burns up the distributor. Problem solved.

My 2 cents it, sounds like a coil if you have a winding or 2 go bad the coil can build the charge in the primary system and release through the secondary only so fast usually the more resistance in the coil the slower this happens, the more cylinders it has less resistance is required to build the field faster. If you have a bad coil or a coil with too much resistance it can cause the exact thing your describing essentialy the coil can keep up with ignition demands for a little bit but starts to fail as it heats up and RPM increases. test the resistance across the primary circuit of the coil and see what it says. You will likely want around 1.5 ohm or higher but no higher than 3 ohm. Also a good spark tester can tell you what the coil is producing a good coil should be able to jump a 25k Volt gap and be a bright blue a weak coil will be more of a orange spark and may not be able to jump that large of a distance