Ok so i havent tried to start my 1977 280z in abut 6 months and it use to run fine, but now when i try to start it she trys to stay running but there is a sound of like pressure releasing and it kills the car as soon as that happens, im only one person so i cant see where the sound is coming from, the only possible idea i have had so far is that the echaust is pretty rotted out and there is not enough back pressure, but im new to working on these older vehicals im more into newer imports but this car was just passed down to me and i have big plans for it so any help would be nice.

Could be a vacuum leak. Is the oil fill cap on? Check all of the vacuum hoses on the intake manifold for splits or breaks. Any vacuum leak on an EFI engine will cause problems.

No engine needs back pressure on the exhaust system. Urban legend.

alright thanks ill take a look tonight when i get off work and post a reply to update

...there is not enough back pressure...

I'll pretend I didn't hear that.

Inspect the intake from the Air Filter to the Throttle Body. Look for splits in the boots or anything that is loose. I once knew a guy who found a Rat in his air cleaner - great for induction. Check the usual suspects: Spark, Fuel, Timing, Fusible links, EFI connection to battery - time to start checking off the simple things...

BTW: Have you downloaded the EFI Bible, Factory Service Manual and Color Electrical Diagram for the '77 ??? If not, please do so (search the forums for links) these documents will help you in more ways than you can imagine...