302 runs rough when warmed up

[Broncopuckett]

I’ve read several threads here about this issue. I have a 302 with Motorcraft ignition module, no points, 2150 2bbl. Pretty stock.
Was running great when on one 10 minute drive last week while sitting at a light, it started running rough, missing, stumbling. Never cut off but not good.

Changed out ignition mod, coil, put on new choke and adjusted it along with curb idle, etc. Checked wires, distributor, vacuum advance (Fairly new), vacuum leaks.

What should I check next? It didn’t start getting rough, it went from running fine to not in one drive. Consistently does every time now.

Help!

 

[SHX669]

So is this a Ford Duraspark system ? I had a similar issue with mine ; it would start and run fine but after driving it for awhile and warming up it wouldn't restart until it cooled down a bit. It was the Magnetic Pickup in the distributor . Apparently when it got hot it would malfunction.
I was scratching my head as to why it wouldn't start - sometimes/ intermittent and a Bronco Brother told me his Buddy had the same issue and to check the magnetic pickup - so apparently it's not real uncommon

 

[Broncopuckett]

Ok, I had read that too but forgot about it. That is something I have not replaced
Thanks!!!

 

[gr8scott]

To test the magnetic pickup, unplug the distributor plug and take an ohm reading between the orange and purple wires.
Between 400-800 ohms is considered good, anything outside that range is considered bad.

 

[DirtDonk]

To add to what Scott said, I use 700 ohms as the high end because in some Ford books it says 700 and some it says 800. So erring to the low side would seem a good idea if they can't figure out which it is.
And frankly, if you're testing it cold I would replace it if it's even close to either extreme.

Paul

 

[Broncopuckett]

Ok, marked dizzy, change the magnetic pick up , cleaned the dizzy up, reinstalled. Now has very high idle. Could the old stator/pick up been so bad that everything else (Carb) was compensating so now back to dial in carb. Thoughts? Am I on the right track?

 

[jckkys]

If the distributor was reinstalled with more initial advance, that would explain the increased idle speed. Why was the stater replaced? It's just a piece of cast steel that has no way to wear out as it doesn't touch the magnetic pickup.
The pickup coils sometimes go bad but they are only about 17 bucks and easy to install. I've done it without removing the distributor. The ignition module and coil are more expensive and didn't need replacement. I don't know what you mean by replacing the choke. Was it just part of the choke? The choke housing, thermostat cap, or the choke plate are all part of a choke. Again these would have nothing to do with your problem.
If the ignition module you replaced was a US made Motorcraft part keep it. Those are far better than current ChiCom junk. The same with the coil.

 

[Broncopuckett]

Meant to say replaced the pick up. So, initial advance causing the high idle? Have the Motorcraft blue wire module. Blaster 2 coil. New vacuum advance. New engine wiring harness. Replaced choke spring with a motorcraft unit...tighter spring than the aftermarket one. Someone mentioned that could be a problem with my initial problem. So, it sounds like I need to turn the dizzy just a bit counterclockwise...

 

[gr8scott]

So, it sounds like I need to turn the dizzy just a bit counterclockwise...

Yes. Do you have a timing light?

 

[jckkys]

I'm trying to translate "choke spring". Do you mean the choke's bi-metal coil in the thermostat cap? If so it's neither tight or loose. When it's cold it closes the choke plate and engages the fast idle cam. Once the engine warms up it opens the choke plate and disengages the fast idle cam.

 

[Broncopuckett]

Finally have it all figured out - It wasn't one thing but a number of little things that started to add up - dizzy was worn and wobbling just a bit, some play in timing chain, back connection in ignition module harness, fouled plugs and worn out 2150. All repaired or replaced (Took 2 rebuilt 2150's to get a good one). Running great once again!