One clean spark plug

[grease]

175238

I started up my new engine recently and have been working through several issues. Getting timing set, rough idle, swapping from FI controlled timing back to mechanical advance, chasing a couple oil leaks, adjusting valves, etc.

I pulled the plugs so I could spin the motor to confirm TDC and found one plug clean. Have you seen this before? I’m assuming this meant that cylinder wasn’t firing.

How do I find the problem. I ordered new plugs and am waiting for them to come in. I megged the plug wires, they seemed good.

I checked the distributor cap, the cap and posts and rotor seemed ok.

Scratching my head and looking for suggestions.

[andrewb70]

How about sharing what engine this is? What ignition system? Details!

Andrew

[grease]

It’s a 406 SBC. Recently rebuilt. Aluminum, angle plug heads (pro top line 220 heads). Eagle rotating assembly with flat top hypereutectic pistons, approx 10.5:1. (Block was zero decked and heads were milled). Comp roller cam and roller rockers. Air gap rpm intake. Small cap HEI System with e-core coil.

[andrewb70]

I'd start with the basics. Was the plug wire attached securely to the distributor? Was it secure to the spark plugs? Check the distributor cap. Is the post for that cylinder ok? Is the rotor good? Is there a break in the spark plugs wire...do a resistance test.

Andrew

[grease]

Cap and rotor are new, they look good. Posts are solid. I did a resistance check of the plug wires, they are good. It may have been a connection problem, but I wasn’t paying close attention when I removed the plug wires. They will be securely connected when reinstalled.

[GoodysGotaCuda]

You can take a spare plug, ground the threads and run the motor to verify spark on that cylinder.

If you have spark, I'd guess the intake valve isn't opening. Pushrod bent, pushrod misaligned, broken rocker, etc.