Technical Multiple cylinder misfire

Alright a bit of backstory before I get into the current issue:

I've got a 1950 Ford F1 with a 1951 Cadillac 331 matched to a T5. I decided last year to switch the ignition over to a pertronix. It worked great initially but since then I have went through 2 different units and decided it was time to go back to points.

While switching things back over I put in new points, condenser, cap, rotor and coil (when the pertronix last died the tow truck driver left my key on and blew my old coil).

The truck now starts up but only runs on 3-4 cylinders from what I can tell by pulling off individual plug wires while its running.

I'm a bit stumped as to what to test now to figure out whats going on. Any help would be greatly appreciated!

 

There is a fellow on here that makes a good external condenser. Condenser is my first thought.

Are the points popping evenly?

Do they have a good spark?

Plug wires, are they good?

Plugs, are they gapped correctly?

Coil connection, is it sound?
A broken wire with an intermittent connection in the ignition circuit will drive you nuts. Look at the coil connection. My ‘65 had a broken wire right at the connection.

 

Wires are cheap fix. That would be my first guess. (Not really. I replaced an electric fuel pump once and it was bad spark plug wires!)
6sally6

 

Is the engine grounded and grounded well? That may explain the petronix failures.

 

Any time one goes through multiple failures of the SAME THING, there is another problem. A LOT of the time it is the indicated bad ground.

Ben

 

The solution to your problem is to give me the Cadillac and I'll swap you a 1950 8RT or even a 302.

This truck sounds bitchin........How about some photos.

 

I have a perfect ground from the base plate of the distributor so I should be good there.

I'll check the plugs and wires but they are only 1 year old and I had no problems with them as the truck was running fine until the pertronix died a week ago.

How do you test a condenser? Maybe I got a bad one.

I've already tested the coil (resistence tests not loaded tests) and it checked out fine.

Also not sure what how to check if "the points are popping evenly"?

I can add pics later when I'm home.

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With the cap off, cranking the engine, the points should have a visible arc and an audible “pop” or “tick”.

What you are looking for is a steady consistent spark. It should spark each time the points open. You can see it better the darker it is in the engine compartment. You will have to have an assistant crank the engine while you watch the points.

If the spark is weak or intermittent, there’s no need to look further until it’s right.

Of course be safe while doing tests.

 

I would make sure the engine was grounded as well. From the factory these had a ground strap going from the engine block to either the firewall or frame.

 

Is it an imported no-name el-cheapo condenser? Don't bother testing it, throw it away. An ignition condenser really has to be tested with several hundred volts DC anyway, a multimeter can't do that kind of testing.

A good condenser once charged up will hold its voltage for a long time, at least a day or so and will bite ya.

 

What is the voltage at the + side of the coil? Are you running s resistor to knock the voltage down from 12v?


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I’ve grounded my engine directly to battery, then from that point to the frame. An ungrounded engine can cause a myriad of issues, including ignition and coolant system corrosion! I would also check for wobble in the distributor shaft......condensers are always suspect too! They’re cheap, just replace it.....

 

Check your dist. shaft for play.

 

Since you changed the cap, I would check the firing order. What do the plugs look like?

 

I'm guessing the truck has been converted to 12 volt, negative ground?

If you swapped the distributor and/or coil, did you wire them properly? On a negative ground system the points should be wired to the negative (-) coil terminal.

If you need a refresher course on conventional points type ignition systems, you might give this a read-thru...

https://www.jalopyjournal.com/forum/threads/hot-rod-technical-library-basic-ignition-systems.983424/

 

The truck is 12v negative ground. Plugs and wires are good. I have 6.4 volts at the coil (.8ohm resistor in line).

I also double checked the ground both at the distributor and the block and they are good.

I took a look at the points with the cap off and am seeing a nice consistent sparking.

I'm guessing the condenser I got is no good? Anyone have a brand they recommend for me to get a replacement?

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I had a similar problem with my 331. It happens to be the back of the point (around the fastening screw) that now and then touched the distributor house and made a bridge. but only once in a while. It was a real pain in the butt to discover.

 

Have you double checked the points gap. Too much of a gap will cause what you are experiencing.

 

Put in a new Echlin condenser from Napa and it started right up. The original condenser I bought apparently was bad. Also here are a few pics of the truck as requested earlier.

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Sweet!

 

Boy, that is a nice lookin' truck. Somebody above mentioned my condensers. Here is an Olds Rocket distributor converted to dual points with one of my external condensers. (The condenser has to be mounted externally because the second set of points take the space where the internal condenser usually mounts.) I believe a Cadillac distributor would be similar. These units can be used on a single point distributor as well.

 

Red50,
I really like the truck,,,,but the engine is the object of my affections.
That is a sweet looking Caddy.
What makes it look good for me,,is the details,,,,and the fact it looks like it was done at home by you.
I enlarged the pic and even though it is not an expensive store bought job,,that is what is impressive to me. You took the time and effort to do a good job and make it your own.
Outstanding!

Tommy

 

Hey Tubman,
Where can I purchase one of your condensers?
I will need one for an old Chevy tach drive dual point I am gonna do soon.

Tommy

 

Thanks. It's an original stock engine with a few bolt ons. Never been rebuilt and has very low miles. Spent most of its life on the floor of a garage. I swapped out the manifold to a 4bbl and changed the exhaust manifolds. Painted it myself, like you said nothing fancy but it does the job.

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