i just did that on the 72.
1. turning the key on will only make pressure for a brief moment. as soon as the relay fails to read the engine turning over or running the pump is shut down. pressure goes to zero
2. during the cranking the relay senses the engine turning over and fires the injectors and a signal to the pump to continue.
3. obviously once the engine starts the pressure continues. mine had 30psi in the rail during the engine running.
4. almost immediately when the engine stops the pressure goes to zero.
not sure if 30 psi is correct cause i've read 2 different pressures in 2 books. but it runs just fine
1972 350sl Red/Blk 117k
1988 420sel charcoal/Blk 140k
1987 420sel gold/tan 128k
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