The FIRST thing to have after purchasing a vette is FSM. The LAST thing to do to a vette is modifications which change baseline specification/parameters, UNLESS it was done on a NEW car, AND, the new baseline specs were put into a chip, AND were recorded on paper.
Otherwise, tune diags is a shot in the dark YUP...
You'll test pump strength and FPR diaphragm spring strength later, but first:
First, cap the return line, AFTER the FPR. DON'T PINCH LINES - you'll damage them, especially if you really pinch to STOP flow.
After disconnecting and capping the line, COLD motor, turn the key on to prime the pressure in the fuel rails. Have a pencil/paper ready (although you know already it's dropping almost immediately).
Note pressure let-off time in 5 second increments (or 10, 15, 30). If (since yours is going to 0 in a few seconds, this won't take long to find.
Pull the FPR vacuum line, and get a whiff. If the motor was cold, you might find gas in the vacuum line. This will indicate a ruptured diaphragm in the FPR. Ruptured diaphragm will make for hard hot restarts, among other things, poor mileage, etc.
Fix, and start over.
If pressure still drops quickly, look for leaks along the entire line, from tank to FPR.
Fix, and start over.
If pressure still drops quickly, your injectors might leak. Put your multimeter on them, and test for resistance. Uneven or low readings could indicate leaking injectors. Pull the rails (with injectors) carefully from the manifold, get a container under each injector, and prime the rails. Look for leakers, and replace if necessary.
A tip for BEFORE pulling - squirt some Armor-All into the injector port if there's any debris in them, and blow away excess, or hit it with the Shop-Vac. You don't want anything getting in the ports behind the injectors into the intake, or anything blocking the o-ring seal at re-asembly.
Re-assemble, and start over. Quick pressure drop now is a faulty pump assembly.
End of static fuel pressure diagnostics. Now do dynamic test, to test the diaphragm spring in the FPR (don't assume it's good, even if new).
BOOKMARK THIS POST UH HUH YUP
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The vacuum line to the FPR is for acceleration enrichment.
Proper function is confirmed on a dynamic pressure test. Increased rpm's (and vacuum to FPR) makes extra fuel available for enrichment. This test however is after static tests have been completed...
