Read a few more comments posted on the internet about hard start issues for the 606 engine.

Read a couple that discussed failure of the glow plug circuit to turn on any glow plugs.

Decided to plug in my block heater. After a couple of hours heating the block, the engine fired off immediately. So guessing that is where the hard start problem is.

I did notice another clue mentioned by some of the posts that pointed to a problem with the glow plugs and not a fuel related issue.

During the latter long cranking periods while trying to start the car, there was unburnt fuel vapor/smoke coming out of the exhaust. When it did start there was a big burst of smoke that cleared immediately.

I'm surprised the engine wouldn't immediately fire off on the hot 100 degree days without glow plugs working.

Will be using the block heater til I have time to work on the glow plug issue.