Well you could be right. He seems to think it is an ignition problem though, and we can only work on the information provided. It would be good to know when the Unpleasantness began. Did it start after the Pertronix conversion, for example.

 

Here's a crazy idea that just might work, after all, you sometimes need to think of solutions that are "out of the box".
Mist the secondary ignition with water and rig up a GoPro or cellphone camera and go for a drive, make it do its thing. Preferably after dark. If you have an ignition problem it should show itself on camera under the correct conditions.
I have not tried this before, just thought of it and would be interested to know if it works.
Dan

 

I was thinking about how I'd ask my wife to ride on a fender or somesuch, but thought better of that idea.
Maybe tape a phone under there.

 

The issue has been around since I got the truck a year and a half ago. That is why I replaced all the secondary ignition parts the first time.
The carb was gone thru about a month and half ago. Truck ran great for about a month then started showing the issue.

In thinking about all this, the shop did say he was having a hard time with the power valve, or whatever Motorcraft calls it. It is the original carb, 2100. and that could be the issue here. He did rebuild the carb.
At the same time I had him remove the ballast wire. I did retest the hot to the coil and the voltage was 9.6 so subsequently tested it with a direct 12 volt from the battery and the problem persisted. I'm putting in a relay to eliminate the old ignition wiring and make sure the coil isn't wanting for voltage. But that wasn't the issue.
I've gone thru and replaced all the high voltage stuff except for the plug wires and I just don't think they are the culprit. That's when I put in the proper coil 1.5 ohmThey are still new and shiny and good.
I do have a set to replace them but haven't got them installed yet.

I'm going to stop by the shop and let the guy have a listen and I'll plant the "power valve" seed of doubt again. Maybe time for a carb upgrade.

Maybe a Ford Shaman, outta be some of those in North Texas.

 

What does that mean, exactly? It isn't complicated. What # is installed right now? A 6.5 is included with most rebuild kits. But if it isn't opening when it should, it will be lean on acceleration, under load. This is dangerous and can burn valves or possibly grenade your engine.

If it isn't closing when it should, then you'll need a fuel tanker to follow around and top off the fuel tank as necessary.

Inspect spark plugs carefully.

 

I agree with Tedsters last line.
Misfiring under a load is almost always spark plug related. When you open the throttle you increase the cylinder pressure, when that happens it becomes harder for a bad plug to fire. Especially if the gap is to wide. We used to bomb test all of our spark plugs in aircraft engines before we installed them. A bad plug that would fire just fine at 120 psi. would become intermittent or stop firing completely at 150 psi.

 

Could be. I've seen some marathon trouble-shooting threads that turned out to be something pretty simple - say, a burnt spark plug terminal inside the boot. A scope would have narrowed that down pretty quick. "Hm, what's up with #6 cylinder??" It gives a place to start investigating instead of just deploying the parts cannon.

Defective spark plugs from the factory aren't unheard of. Rare but it happens. Also user error. I heard someone mention once he was changing spark plugs out with a graybeard watching and shooting the breeze, and he accidently dropped a spark plug onto the hard concrete a few feet. He picked it back up and started to install it. The old guy said "write down what cylinder that is, so you know what spark plug to replace when it starts misfiring". And danged if the guy wasn't on to something. The porcelain can get cracked internally without being visible.

 

The old guy was right. The rule in the aircraft world is drop it once, drop it twice. The second time in the trash can. And those aircraft plugs are $40 each or more, depending.

 

Yes, I've seen a dropped plug with a small crack and it eventually caused carbon tracking that shorted the plug under load.
I've also seen a plug that was cracked when installed not using a good quality plug socket.
When buying plugs you don't know if the idiot behind the counter dropped the whole box when he went to get them in the back.

 

The plugs are all fairly new, had then all out a week ago to check the gap and inspect them. Everything looked fine, dark tan color, nothing out of the ordinary. I've never dropped a one of them.
If it was one or two cyls misfiring i would be able to tell by the sound but this is a different sound, a rumble of misfire noises.

Head scratching...

 

Lots of ideas and good advise here. Let me toss another thing out there. When I got the truck it had the Pertronix igniter I in it. It still had the ballast resistor wire as well and a MSD 8292 low resistance coil.
I have read in a few places running the Pertronix with less than 12 volts might hurt the Pertronix unit. Could that possibly cause this issue? Primary side of things but controls the secondary side as well.

 

Pertronix Ignitor is a very simple critter, known formally as a Hall Effect transistor, basically an electronic "switch" triggered by magnets instead of mechanical points bouncing off lobes. It pretty much either works, or it doesn't.

It might get confuzzled with wonky connections or something like that. Maybe it's been mentioned before, but a frayed distributor wire or poor connection in thar when the breaker plate moves back and forth might do some interesting things. For test purposes try disconnecting and plugging the vac advance port and take it for a spin.

Another common error, sometimes people will mistakenly omit that uninsulated stranded copper bonding jumper wire that grounds the distributor housing to the breaker plate when converting to the Ignitor module. Make sure it is still present. The module needs a good solid low resistance ground, same as the contact points. Even so, measure the resistance between the NEG battery post and the breaker plate. The limit is 0.2 ohms, subtract the meter lead resistance from your measurement to get an accurate figure.

 

I have run a Pertronix I with a stock coil in my Mustang on low voltage resister wire for 20 years without a problem. When I first got my Ranchero the 292 had a Pertronix I and coil and ballast resistor and it had a constant miss, changed it to straight 12V and the miss was still there. Hair pulling time. I then reset the .030 gap to .020 and it purred like a kitten. I didn't like that fix so I swapped it for the Pertronix II and didn't have any further problems..