I experienced a
“An error occurred while starting up the preloader: it did not write a startup response in time.”

The problem was that it took more than 90 sec for the passenger preloader process to start…..

Solution:
cp $(passenger-config about resourcesdir)/templates/standalone/config.erb nginx.conf.erb
edit the nginx.conf.erb in your Rails.root and add
passenger_start_timeout 900;

after this:

• stop passenger
• start passenger like this: RAILS_ENV=production bundle exec passenger start -p 3006 –nginx-config-template nginx.conf.erb -d
• … wait … it worked for me 🙂