47 V8 ignition mystery

[Bored&Stroked]

One of the challenges can be that distributor machines don't test anything to do with the secondary side of the equation - so while the distributor may "spin up" just fine on the machine, when you put the cap, rotor, wires and plugs in the engine, it may leak voltage to strange places. Due to this, on my distributor machine I have a custom setup to test the engine ignition system --> coil(s), cap, wires and plugs.

This is particularly important on the ole' Harman Collins dual-coils with the yellow mid-plate. Those mid-plates can leak secondary spark/voltage all over the place - the problem is quite typical. The symptom is that 4 cylinders will run fine and 4 will either not run, or have terribly intermittent sparks and dropped cylinders.

Here you can see "Frankenstein's Tester" in action: LOL

https://youtu.be/3xduaVyzx10

[cas3]

Thats a cool machine Dale! Takes the guess work out of the equation for sure.

[ford38v8]

Now, that's a work of art!

[Lawrie]

Man I like that, I have a home made distributor set up machine, but I only use plugs with a very wide gap,I think I will make a setup like that for extending the gap.
I set up all. my V8 distributors on it, and in this last week a pile of my model A ones with a vac advance,
it is very easy to set up and alter the advance amount and curve,
My machine is not as sanitised as your one.but sure does a great job.
Lawrie

[Lawrie]

A couple of pictures for my post above

[petehoovie]

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Originally Posted by Lawrie

A couple of pictures for my post above

[Old Henry]

Verdict (as us legal beagles are want to say): It appears to be the condenser that was guilty.

To refresh your memory, I had purchased a remanufactured distributor from Southside Obsoletes, replaced the old points, and put in my old condenser that still tested .35 mfds. Then I had all kinds of cylinders miss-firing. It seemed that the spark coming out of the coil was steady but was not making it to all of the cylinders. So, I figured it was the sparkplug wires and ordered all new ones along with new boots and both outer and inner distributor caps to replace. While waiting for those to come I sent the distributor to Michael Driskell to check out to make sure it wasn't the problem. All he found was that my correct gaps of the points did not make the dwell correct so adjusted that and said my condenser was bad even though it had tested .35 mfds and replaced that and returned the distributor to me. In the mean time all other parts had come to replace but I waited until I got the distributor back to put in and see if it fixed the problem without having to replace all of the other stuff. To my great and pleasant surprise, it did and I didn't have to replace the rest.

I pondered on the question I asked myself why the new condenser that only tested at .31 mfds (.35 being optimal) worked better than my old one that tested optimally. I concluded that there is more to the adequacy of a condenser than just its capacitance. Over time, the paper and foil that it's made of deteriorates and ceases working even though its capacitance tests optimally. (Even though that seemed like a new idea to me, it is more likely something I knew and forgot.)

So, lesson learned: Always replace the condenser whenever replacing the points, even if their capacitance still seems correct.

[corvette8n]

Glad you got it fixed, don’t forget to carry a few good condensers with you.

[35fordtn]

Old Henry glad you are up and running.

Your distributor had 42 degrees of dwell and a bad condenser, with either one of the two IÂ’m surprised it ran. Testing just the mfdÂ’s of a condenser is not a true test. We heat them to 160 degrees and test the mfdÂ’s and the leakage as thatÂ’s the typical failure. Your issue was the leakage, it wouldnÂ’t hold a charge for more and than a millisecond. A early ford really can run fine on .20-.45 mfdÂ’s. I think ford used .36 since some vehicles like busses and truck sat idling a lot where the higher mfd helps from burning points at idling for long periods.

Ps the new condenser is a standard fd72 and I have never after using and selling well over 400 of them have ever seen one go bad

[Old Henry]

All of my life the routine was to replace points and condenser together until a few years ago when I read an article (that I can't find right now) about condensers that told how too high or too low mfds would cause pitting and peaking of the points, too high one way, too low the other, and that once a condenser was found that did not pit and peak the points to keep it as they are rare. So I did. For years now I've never seen any pit or peak on any of the points I've replaced so have just kept the same condenser until now that something worse than pitting and peaking occurred. I'll go back to my routine of replacing the condenser with the points every time and get the points from NAPA the same as I get the points and rotor even though I may end up with some points pitting and peaking.

[Old Henry]

The sad saga continues . . .

Unfortunately, the new condenser was not the "silver bullet" that would kill my ignition problem nor solve the mystery. It only helped for about a day when the same old problem returned - skipping beats under load.

I thought maybe the coil. The impedance of the high tension coil was only 6,440 ohms, not the 10-11,000 ohm it should be, but I pulled off the high tension wire to the distributor and plugged in a short one and watched the spark at the end near a head bolt. The spark was strong and consistent - never skipping a beat so I thought it must be OK.

Since I had already replaced all spark plugs and distributor, all that was left were the spark plug wires and distributor cap. So, I ordered whose and knuckled down to change them when they arrived.

Removing the old wire conduits and the cap was the first time I had been able to inspect the cap. It looked like the attached photo so I thought for sure it must be the problem and replacing it would solve my problem. Again, as soon as I got all of that replaced I tried the engine, drove the car around, and it seemed to have fixed the problem - for about a day. UGHH!

When the old problem of stumbling under load returned I turned to examination of the spark plugs I'd just put in. Oddly enough, the bracket on #2 was smashed right down to the tip without any gap at all. That would seem to be a problem. I gapped it properly and checked all other plugs. They were all gapped correctly but #1 had black moist soot on it. The plug fires OK so I hope that's not the problem

I hoped fixing the plug would fix the problem and tested it by climbing a short very steep hill. I had full power with all cylinders firing. So, we decided to do a little 350 mile overnight road trip the next day.

As soon as we set out the same old problem returned - stumbling under load but otherwise fairly smooth on level high speed. Needless to say, the 172 miles we drove that afternoon was not as relaxing as usual with the engine stumbling most of the way.

I hoped it was a fuel problem, not ignition, so next morning before heading home I hooked up my timing light, clamped the sensor to the coil high tension wire and duct taped the light to my cowl so I could watch the light and know what was going on with the spark while we went down the road. (See attached photo) Unfortunately, the stumbling showed in the light flashes - more when under load so it's still an ignition problem.

I don't know what else to do.

Any ideas?

[JayChicago]

Have you tried a different coil? My understanding is that coils (like condensers) will often work fine at first, but then start to fail when they get warm from usage. So looking at spark output in the garage may not tell you how it will perform later.

And what about that plug you found with tip bent closed? That's curious! Have you pulled that plug to see what it looks like now?

[petehoovie]

Originally Posted by Old Henry

The sad saga continues . . .

Unfortunately, the new condenser was not the "silver bullet" that would kill my ignition problem nor solve the mystery. It only helped for about a day when the same old problem returned - skipping beats under load.

I thought maybe the coil. The impedance of the high tension coil was only 6,440 ohms, not the 10-11,000 ohm it should be, but I pulled off the high tension wire to the distributor and plugged in a short one and watched the spark at the end near a head bolt. The spark was strong and consistent - never skipping a beat so I thought it must be OK.

Since I had already replaced all spark plugs and distributor, all that was left were the spark plug wires and distributor cap. So, I ordered whose and knuckled down to change them when they arrived.

Removing the old wire conduits and the cap was the first time I had been able to inspect the cap. It looked like the attached photo so I thought for sure it must be the problem and replacing it would solve my problem. Again, as soon as I got all of that replaced I tried the engine, drove the car around, and it seemed to have fixed the problem - for about a day. UGHH!

When the old problem of stumbling under load returned I turned to examination of the spark plugs I'd just put in. Oddly enough, the bracket on #2 was smashed right down to the tip without any gap at all. That would seem to be a problem. I gapped it properly and checked all other plugs. They were all gapped correctly but #1 had black moist soot on it. The plug fires OK so I hope that's not the problem

I hoped fixing the plug would fix the problem and tested it by climbing a short very steep hill. I had full power with all cylinders firing. So, we decided to do a little 350 mile overnight road trip the next day.

As soon as we set out the same old problem returned - stumbling under load but otherwise fairly smooth on level high speed. Needless to say, the 172 miles we drove that afternoon was not as relaxing as usual with the engine stumbling most of the way.

I hoped it was a fuel problem, not ignition, so next morning before heading home I hooked up my timing light, clamped the sensor to the coil high tension wire and duct taped the light to my cowl so I could watch the light and know what was going on with the spark while we went down the road. (See attached photo) Unfortunately, the stumbling showed in the light flashes - more when under load so it's still an ignition problem.

I don't know what else to do.

Any ideas?

[Old Henry]

Originally Posted by JayChicago

Have you tried a different coil? My understanding is that coils (like condensers) will often work fine at first, but then start to fail when they get warm from usage. So looking at spark output in the garage may not tell you how it will perform later.

And what about that plug you found with tip bent closed? That's curious! Have you pulled that plug to see what it looks like now?

I thought I had another coil to try but couldn't find it. I may have to buy another just to see.

The straightened plug is fine. I just checked it.

[Terry,OH]

Both the coil and the ignition condenser can fail after heat builds up and yet, when cold, can work properly. If you have had your original Ford coil rebuilt by Skip Haney, I would suggest it is most likely good. Who manufactured your plugs and what number are the plugs? Does your engine have a heavy battery ground cable bolted to one of the head studs? Which cylinders are not firing correctly?How do you explain the plug electrode being bent when you checked plug gap before installing?

[deuce_roadster]

I would guess that either the reach of the plugs is too long or there is enough carbon built up to hit the ground strap on the plug. How many miles are on this engine? What make and plug number are we talking about? I would certainly replace that cap and not write anything inside of it. I would also double check the ground of the engine to insure it was clean and tight clear to the battery. If loose and dirty, it might fail as the engine heats up.
An old timer once told me that all electrical troubleshooting begins with and at the battery.
Have you used a jumper to eliminate the resistor when the poor running is happening? It could cause problems too as well as the ignition switch itself.

[Seth Swoboda]

When you say it stumbles under load, it's when you are hard on the accelerator pedal? How do you know you don't have a problem with your accelerator pump?

[47topless]

You could just buy one of those Blue Streak (Flame?) tube coils at NAPA or O'Reilly, depending on your system, with or without built-in resistor, and test that. They are very inexpensive, and you would then have an emergency spare.

[Old Henry]

Originally Posted by deuce_roadster

Have you used a jumper to eliminate the resistor when the poor running is happening? It could cause problems too as well as the ignition switch itself.

Now here's something really weird.

I just connected a jumper wire from the battery to the coil, bypassing the resistor and all wiring through the ignition switch. I had actually done that once on my trip to see if it helped. Both times it actually made the problem MUCH WORSE. I could hardly climb the hill in front of our house.

Why is that? Can't figure that one.

[Old Henry]

Originally Posted by Terry,OH

Who manufactured your plugs and what number are the plugs?

Originally Posted by deuce_roadster

What make and plug number are we talking about?

Spark plugs are brand new Autolite 216 just installed. Same as I've used for years.