Hey guys I have been chasing this issue for a bit and nothing I am trying is curing it. At idle it runs fine but every now and then there is a slight miss, sometimes a quick miss, sometimes a bit longer but it never dies. Take the car out on the road and it runs fine, nice throttle response and no noticeable stumbles or anything. The other day I pulled a plug wire while it was running and noticed that when I heard the stumble, there was also a stop in spark, very briefly. It will do this to what ever plug wire you pull. When it stumbles for a second, there is no spark. I have tried a new coil, new condenser, and pulled the cap. Looks ok inside. Any ideas? This engine has only been in the car for around 2 years and this slight stumble was not there when I first installed it. Engine is a ‘36 LB, bubbas distributor with crab cap. Converted to 12 volt. Converted 12 volt generator, 1957 ford voltage regulator (30 amp)
What kind of wires and terminals? Are they run through conduit? Essentially, is there a place they may be shorting?
Have a similar setup, had a similar problem, after trying a dozen things ended up replacing the crab cap and resolved it.
I had this problem on an OT 65 Mustang. I was going to change the plug wires anyway. Well, when ever it was damp outside, the engine would stumble at start up and then very intermittently while driving. I also noticed an arc at times from the plug wires to the block. It all stopped when I changed the plug wires.
First I’d Run the engine in a totally dark environment. Any errant spark will be visible. Pulling a plug wire during an idle should always drop continuity somewhat.
I’m not very literate on FH’s, but it the loss of spark during the miss happens on all 8 wires, I’d go back to the source of the spark. As I recall the crab distributor (I only had one, but engine was stuck so never ran it) used an external coil. Put your timing light on the coil wire and see if spark stops during the miss. If the coil is dropping spark, and since it’s a replacement and does the same thing, I’d be going over the run side on the 12 wire going to and from the ballast resistor. A quality DVM will be able to detect DC interruptions if you pay attention to below the voltage number and focus on the scale. An O’scope would be invaluable. To me it seems like the coil is not getting voltage briefly, to keep working. Chaffed wire, bad ignition switch, etc. Edit: a quality ****og meter to monitor the dc voltage to the coil, would see the needle swing if voltage dropped.
I've read but never experienced the little stud that transfers power from outside the distributor housing to the inside point bar can go bad. Evidently they can lose connection.
I’ve had this very thing happen to me. I also installed a new wire for that connection. Took a good while to trace that problem.
Strange thing I am noticing is that when the car is hot, up to temp and running awhile there is no misses. I can let it idle and all is fine so it seems like it is only doing it when cold.
Well, there’s still a wire that goes to the coil to charge it. But other good points mentioned above as well.
If you're running your plug wires through the original conduits, that could be your problem. Plug wires with inferior insulation can leak and short to other wires and to the conduit. Not one of Ford's better ideas. Where did you get your wires? Are they a major brand, such as Packard? Radio suppression wires can be a problem, too. I've gotten wires in the past that leaked so bad it was a lightning show in the dark. Remember also that in this new age, just because it's new doesn't mean it's good. I know it's a pain in the ***, but pull the wires out of the conduit and give them some space to see if that makes a difference. Check the cap and rotor under magnification to see if there is any sign of the beginnings of carbon tracks, also. Check for signs of burn through on the rotor to the distributor shaft. An internal flaw in the coil is an unlikely possibility, but it can happen. Beginning about 1956, Ford used plastic separation clips to keep the wires away from each other. That might tell you something. Hope this gives you some insight.
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