ignition problem help

[shelbyhertz66]

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

[trotrof1]

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.

[Bob Gaines]

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

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.

[shelbyhertz66]

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.

[Bob Gaines]

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.

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.

[trotrof1]

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.

[JFriend]

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.

[shelbydoug]

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?

[shelbyhertz66]

Thanks everyone for the great ideas for trouble shooting this kind of issue, hopefully it will help others as well.
So here is an update with what I found.
After trying the things suggested I pulled the distributor and replaced it with a known good dual point one and the problem seems to be gone. Drove it about 30 miles and no miss firing etc. after about 20 miles also changed the coil just in case it was failing when hot, that said I think the distributor has some kind of issue , to me the corners on the point cam seem a bit worn down? but still need to dig into it more as there may be something else.  good thing as I know there is a for sale sign around here somewhere!
thanks again.

[rhjanes]

I'm wondering.....Could the distributor shaft bearings be worn?  I had my 302 get that issues several decades ago.  Car had maybe 110,000 on it and just started stumbling and progressively getting worse.  I tried changing points, plugs, rotor, distributor cap.  Nothing helped.  Since I worked in an auto parts store at the time, one of my coworkers had drag cars.   He suggested swapping in a rebuilt distributor from the back.   FIXED. 
The cam lobs do have a rounding to them.  The rubbing block on the points is hard plastic and if the lobs had a sharpness to them, there would be quick wear on the points block.   

[shelbyhertz66]

Bingo! I think,
I had not checked the wear on the distributor bushing and when I moved the shaft where the rotor attaches from
front to back and side to side there is way too much slop. No wonder the points aren't functioning properly when the shaft is flopping around like a wounded tuna. If there is .025 slop and the point gap is .021 you do the math.
thanks again.

[trotrof1]

Is the distributor original to the car? Can you give us the mileage on that unit?

[shelbyhertz66]

So the car and engine have 49,000 original miles , however the distributor was replaced with a service hipo
distributor sometime in its life and, I replaced it with a correct one but missed the fact of bushing wear
can't really say how many miles on it must be a lot.

[shelbydoug]

So the car and engine have 49,000 original miles , however the distributor was replaced with a service hipo
distributor sometime in its life and, I replaced it with a correct one but missed the fact of bushing wear
can't really say how many miles on it must be a lot.

Yup. The play needs to be limited to .001". If the points cam wobbles at all when you wiggle it, it needs to be replaced. Usually knurling the shaft is enough, certainly for the amount of miles you are likely to put on the car now.

Every .001" it moves, the points setting is off .002". So there is no way to set the points accurately or set the dwell. Those need to be within .001".

Not to worry though, they are not complicated to have rebuilt accurately but I would recommend that you seek out a specialist and discuss the issue of play in the points cam assembly. So everyone is on the same page of what needs to be done and what will be done.

[s2ms]

If you decide to have your distributor restored, I highly recommend Jim Woods, "rockhouse66" on this forum.