I have a vacume leak somewhere and can't find it the car back fires and
runs rough I have changed all sensors and plugs cap wires timings on
compression was 150 to 155 can anyone help

Rory[&o]

 

you check around your intakes (upper and lower). I've blown a lower intake gasket before and it hissed at idle but no back fire. Went home sprayed some carb cleaner around it while it was at idle to see if it would rev, and it did so. So i knew i had a lower intake leak. While i was at it i also replaced my valve cover gasket to the rubber type gasket they dont need RTV or anything.

Just spray the carb cleaner around your intake while at idle and see what happens.
And also check all hose connections and hook ups.
GL

 

Since you mention sensors, I assume this is a later model so, I'm thinking maybe an EGR issue. Is the idle rough too? It may be stuck open. Usually, an "air leak" will make it idle faster.