how can i know if the fuel pressure regulator is bad?
You can try the FPR suck test, I am not 100% sure if it will work for your grand prix, but I think it will.
Chugging - Grand Am Owners Club Forums
Credit rixGAphx
SUCK TEST - FPR
This test is used to identify a Fuel Pressure Regulator with a damaged internal diaphragm.
The FPR has a spring-loaded valve that the limits the maximum fuel pressure to 45 psi (54 psi for ‘02+ engines).
At idle and low speed cruise (less than 2500 rpm), the system must have 9 psi less pressure; this is accomplished by intake manifold vacuum pulling against the diaphragm and causing early return of fuel to the tank.
When the diaphragm ruptures with age, then the 9-psi drop not longer occurs and raw fuel is pulled/pushed into the intake manifold; this causes the engine to hesitate upon acceleration (since the fuel pressure can’t step-up the 9 psi) and a flooded condition when starting the engine after running short errands.
TEST:
* Locate FPR at end of fuel rail.
* Identify small vacuum hose from top of FPR to Intake Manifold; disconnect tube from intake manifold, and inspect for cracks, leaks, poor connection.
* With engine ‘off’, a mechanic would use a Might-Vac or similar vacuum tool to suck on the tube against the FPR.
* The FPR *should* ‘hold vac,’ about 14 psi; if it doesn’t, then the diaphragm has failed and a new $50 FPR is in order.
* In the absence of a Mighty-Vac, use your lips to suck on the tube against the FPR; again, it should ‘hold vac’, like sucking on a soda straw with your finger over it.
* There will always be a *slight* odor or taste of gasoline present, which is of no concern.
BUT, a ruptured diaphragm will allow a slug of raw gasoline thru the tube and toward your mouth, which becomes quite unpleasant; use a rag for mouth protection, or use some clear aquarium tubing in lieu of the stock vacuum tube, so you can see approaching gasoline.
