1980 Tercel running on 3 cylinders

Cylinder #1 on my Tercel’s 3A engine does not fire. I’ve changed the plug, wire, rotor and distributor. Other suggestions?

How did the old plug look?

How often has it had valve adjustment? Maybe burned valve.

Do a compression test.

Install a test plug on the #1 wire and LOOK at the spark. What YEAR Tercel?? mileage??

Checking the compression should be the first step; assuming there actually is a spark jumping the plug gap on No. 1.

If the compression is good then things like a weak/broken valve spring or intake gasket leak could be considered.

Old plug had dark brown sooty-looking deposits.

1980, 111,000 km. If no spark on the test plug?

Beware of non-OEM ignition parts.