I am currently working on a 85 vett with a 350 tpi in it. Every time we go to start it we hear a hissing noise coming from under the upper plenum, it will turn over but never start. When you stop turning it over the noise returns for a good 5 to 10 seconds depending on how long you turn the engine over. The car has all new injectors in it, new spark plugs, and a new fuel pressure regulator. Any help would be greatly appreciated. We are at a stand still on where to go next.

 

.. How did the old sparkplugs look? Oil fouled? Wet? Dry? White, grey, or tan insulator?

.. How are the new plugs now? Wet? Dry? Clean?

.. Got spark at a plug when cranking it?

.. Take a fuel pressure reading now?

.. Check ignition timing with a timing light? Maybe a worn out timing chain slipped cam/ignition timing?

.. Compression check on all 8 cylinders? A leaking valve may be giving the hissing sound. But it should still start.

.. When key turned on, fuel pump relay gives 2 seconds of pumping... then oil pressure switch supplies juice to pump from then on after starting...