Hello. This is my first post. I have a mind boggling spark issue!

My car is a 1966 Chrysler 300. 1972 440

Problem: No spark to #7 plug

New plugs, wires, VR, cap & rotor, and coil.

Used a spark plug light tester, nothing.

Checked cap. Looks fine.

Tried a couple different plug wires, still no spark.

Does start but of course runs rough.

Distributor is from 1972 and converted to electronic.

Any helpful thoughts would be great!

 

Did you try swapping the plug and wire of cylinder 7 with another cylinder to see if the problem moves? (maintain the correct firing order)

Is cylinder 7 other wise healthy as far as having good compression?

 

Thanks for the reply!
Yes I have tried 2 brand new spark plugs.
Engine has headers. After running the motor for 30 seconds the header on the 7th cylinder is not hot like all the others.
So I then bought the light tester which shows a normal spark on other wires. I did swap out a couple different wires but still no go.
I have not tried the compression test as I figured that wouldn't effect the spark issue.
I tested all the contact points on the distributor cap and all seems good.
Very confusing!

 

You said you used a spark plug light tester. Is the cylinder misfiring or are you basing the problem on the tester results? I'm guessing by what you replaced your problem isn't electrical. Compression, ignition and fuel are the 3 keys to a good running cylinder.

 

There is no spark according to the tester light. Also a tell tail sign is very little heat on the header on that cylinder. It's warm from the other cylinder firing normally but I can easily touch it while the others are way to hot. Back firing into the exhaust at Idle, which it barely runs at. At 2 thousand RPM it runs much better but still no spark.
Spark plug has fuel on it when pulled. I am sure it's getting fuel.
This all started while driving. It ran good then started missing really bad. Thought for sure it was the coil from reading in this forum. But nope...

 

Good Morning.... Very odd..... Try checking the spark with a 1/8 gap up against a piece of sheet metal, and see if it has any spark?
If not... If you still have the old Distributor Cap, put it back on and see if you have any spark?
Also: Question: You have good strong spark to all the other Spark plugs? or is it weak?
Number 7 Cylinder is the long run for the spark plug wire.... So if you get any spark out of the cap to a 1/8 gapped ground... that should tell us the story more about whats happening.... You can also use one of the old or just a shortest spark plug wire to test it...

Hope this kind of makes sense.... Keep us posted...

 

Thanks Bob, I'll give that try.