hi All,
So My 66 Shelby had been running fine, then yesterday seemed to start normally but in just a few miles it
started to miss and progressively got much worse i barely made it home and into the garage ,kept stalling and running rough. I changed the points and condenser and fuel filter, seems to be getting fuel also plugs look sooty
replaced them still runs terrible , I cranked the engine with the key off and noticed spark at the points? also when it was running the tach is off on the rpms also the timing light doesn't seem to work correctly only flashing
occasionally I checked the timing not long ago and was perfect I am totally lost as to what to check any suggestions would be appreciated. could a bad coil do any of this?
thanks,
Dave
Key on engine off you should have batt voltage at the primary + wire at the coil. On my car I got approx 6.4 v at same wire plugged onto coil + terminal with 12.39 batt voltage.. make sure your secondary coil wire is fully seated in the dist and coil tower. physically move your wiring and check for weakness in the insulation from age and heat cycles. I had a 55 thunderbird with running problems and the wiring passed a visual test but was degraded under the insulation so do a wiggle test for sure. The connection at the ignition switch can be problematic also.
Quote from: shelbyhertz66 on September 28, 2026, 03:38:24 PMhi All,
So My 66 Shelby had been running fine, then yesterday seemed to start normally but in just a few miles it
started to miss and progressively got much worse i barely made it home and into the garage ,kept stalling and running rough. I changed the points and condenser and fuel filter, seems to be getting fuel also plugs look sooty
replaced them still runs terrible , I cranked the engine with the key off and noticed spark at the points? also when it was running the tach is off on the rpms also the timing light doesn't seem to work correctly only flashing
occasionally I checked the timing not long ago and was perfect I am totally lost as to what to check any suggestions would be appreciated. could a bad coil do any of this?
thanks,
Dave
It definitely sounds like ignition . I would check your coil first. That doesn't go bad often. It could also be the resistance wire going bad. You will need a ohm meter to properly test. Your shop manual or You tube will be helpful on how to test.If those things are good I would check your ignition switch to see if it is going bad.The ignition switch failing is best to just substitute to check given a intermittent problem there may not show up in testing. those are the things I can think of to be the most logical but there are other things I am sure. I hope this helps.
Thank you Bob and everyone ,
For taking your valuable time to help with this issue, always tremendous help
on the forum.
I am still working through the suggestions no luck yet. I do believe its in the ignition system somewhere as i have checked the fuel delivery and pretty much eliminated that. I am kind of pointed at the coil or tach as the
tach is way off on rpm when this is occurring but works fine when its not so is the tach causing the problem or is the problem causing the tach to be off I have to be away from the car for a while but will update when I know more.
Thanks again.
Quote from: shelbyhertz66 on September 30, 2026, 10:02:52 AMThank you Bob and everyone ,
For taking your valuable time to help with this issue, always tremendous help
on the forum.
I am still working through the suggestions no luck yet. I do believe its in the ignition system somewhere as i have checked the fuel delivery and pretty much eliminated that. I am kind of pointed at the coil or tach as the
tach is way off on rpm when this is occurring but works fine when its not so is the tach causing the problem or is the problem causing the tach to be off I have to be away from the car for a while but will update when I know more.
Thanks again.
You can by pass the tach to eliminate that possibility by unplugging it from the ignition switch and also from the resistor wire to the coil and then plugging the lead from the ignition switch and the one from the resistor wire together just like on a non tach car.
I checked the resistance on a known good yellow top coil. It read 1.3 ohms across the bat and coil primary terminals and 8.35 ohms across the secondary tower and the two primaries separately. just so if you need a comparison.
Not sure the history and your confidence level in the coil, but I've found that's a weak spot, especially with repro coils. They used to be so rock solid no one ever considered them going bad, not any more. If you have a spare, swap it in and give that a try.
Lately Ford distributors have been showing up with twisted drive pins that hold the drive gear in place.
The Clevelands for some reason are more common failures.
What I noticed is that it is more common for this to happen if the distributor was out for a complete rebuild.
I have to assume that the wrong strength roll pins were used in the rebuild?