Most adjustable fuel pressure regulators will not hold pressure after the car shuts down. They're built differently than the stock FPR. I've had both a Paxton and BBK and they leak down almost immediately.
I put a stock replacement on when I found out that the Paxton was ruined from alcohol and it would not leak down, so I know it wasn't leaking down from the fuel pump side.
It may be that cars with these type of FPRs just take longer to start since they don't have stored fuel pressure like the stock regulators do. 3-5 seconds seems awfully long. I know my car doesn't take that long to start. 1 sec at most. But, since this seems to be a new issue, I would suspect a problem. Let us know what you find out.
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351W 89 Mustang GT Convertible
[This message has been edited by jimberg (edited 07-09-2001).]