Como dizer "ir pras cucuias" em inglês

Also:
went to the dogs (ruined).

as in: "His business went to the dogs when the economy soured."
(source: WordWebonline.)

Also, "to fall flat."

Para dizer que algo não deu certo mesmo, falhou, foi para o espaço, sugiro também "go up in smoke".

Do Thefreedictionary:

Go up in smoke: if a plan or some work goes up in smoke, it is spoiled or wasted.

When the business went bankrupt, twenty years of hard work went up in smoke.
Quando o negócio faliu, vinte anos de trabalho duro foram para as cucuias.

To fall apart

To go bust

Mazars said more beer makers were likely to go bust as the competitive market and the squeeze on consumer spending continue to affect sales. The Guardian

In some contexts "go south" is an option:

The stock market is headed south again.
Source:dictionary.com

If no spark who knows but could be the crank sensor went south. I have had all these situations except a bad relay.

Se nenhum problema nas 'velas' (do carro), quem sabe/vai saber? Mas o poderia ser que o sensor de manivela/sensor de vibrabrequim 'deu ruim' (foi pro saco/foi pro sal/foi pras cucuias). Eu tenho todas essas 'possibilidades' exceto a de um relé avariado...

Source: discussion on Car Talk Community site.