Fueling & Injection - Fuel pressure questions?

I'm helping a friend with his 98 z28.. It has a small cam and idles fine for about 20 seconds and then just surges so bad it dies... I was watching the fuel pressure gauge and it surges with the motor. It starts around 60psi and then drops to about 45psi... Shouldn't it hold a steady 60psi? its a stock fuel system with aftermarket fuel rails.. Checked for vacuum leaks and didn't find any...Have any ideas what it could be?

does it drop when the engine drops rpm?

does it drop when the engine drops rpm?

yes.....

Check the voltage to see if it fluctuates with the engine surge.
If your alternator voltage drops off, it can effect the pump output & also the injector operation.

Does it drive normally?

Yes it driveS down the roAD fine but when you come to a stop and sit it will surge and die... The cam is not that big to be causing it to surge and die. Can the security cut the fuel? Its turned off in the tune but the car wont start sometimes when the security light is on. You have to cycle the key on and off to start it..

any ideas?????

my guess would be on the voltage to the pump still.

if your rpms go down the belt will not spin as fast causing not as much power out of the alt. then it causes the pump to lose power and then it starts to need more fuel but there is no power for the pump to compensate so therefore the car dies. that would be the first thing i would check.