low & no spark on #3 cyl

[James G.]

Engine runs rough. While at fast idle I ground tested each cyl and #3 spark was intermittent/absent. All others had stead/regular spark to ground .I replaced the spark plugs with new W16, then the re-timed the engine with test lamp, then replaced the coil, still no improvement. I've ordered new upper dist body and rotor. Hopefully this will be the fix.
Any suggestions on what I'm missing?

[Patrick L.]

Sounds like it could be a carbon tracked cap/housing. Take a good look at it and sometimes the tracking can be erased.

Also it could be cracked.

[James G.]

New upper dist body and rotor. Not idles really good now but hesitates to take throttle, running kinda rough coming up in RPM to fast idle +. Hummm, is it time to address fuel demand problem?
All inputs surely welcomed.
Jim G.

[wmws]

Try fattening up the idle mixture a bit. If that doesn't help clean all passages in the carb.

[Jacksonlll]

Check your compression to rule that out.

[James G.]

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Idle mix and compression, good ideas. Two I'd not thought of. Was focused on electrical.
Many thanks.
All other inputs sure welcomed.
Jim G.

[alexiskai]

If a short occurs within the distributor body, it often affects cylinder 3. You'll find out when the new one arrives. If that doesn't help, here's a thread from '17 describing something similar with the #1 cylinder. The OP never circled back to report the fix, though.

https://www.fordbarn.com/forum/showthread.php?t=216127

[Chuck Sea/Tac]

Are you saying you checked the actual spark from the spark plug to ground, or are you saying you just shorted it out and it made no difference on number three. If it’s the latter, then it could be a vacuum leak on the intake.

[ryanheacox]

Originally Posted by alexiskai

If a short occurs within the distributor body, it often affects cylinder 3. You'll find out when the new one arrives. If that doesn't help, here's a thread from '17 describing something similar with the #1 cylinder. The OP never circled back to report the fix, though.

https://www.fordbarn.com/forum/showthread.php?t=216127

Come to think of it, I'm pretty sure my original distributor body started arcing from the #3 contact. Interesting observation.

[alexiskai]

Originally Posted by ryanheacox

Come to think of it, I'm pretty sure my original distributor body started arcing from the #3 contact. Interesting observation.

I don't have personal experience with this behavior but that's what I've heard. I'm not sure why it is. I couldn't find any images of a cutaway body to show how the wiring is run, but I found the diagram attached below from a MAFCA seminar. If the diagram is accurate, the body is axially symmetric – so there's no reason wire 3 should fail more than wire 2.

If replacing the distributor body solves the problem, I hope the OP will run some tests with a multimeter across the contacts on the bad distributor body to see whether the #3 wire has any measurable anomalies.