rsc350

When I turn on the key the pressure does not climb. Key on key off a few times, no pressure on the guage. Normal? The TBI guage directions indicate turning the pump on and off a few times should build pressure with out running.

Once cranking the guage climbs to 12 PSI and stays constant while running and heavy reving. My stock FPR turned adjustable on the TBI is regulated almost all the way up on the tang of the regulator (more spring pressure). Should that pressure not be higher than 12PSI?

Once the engine is shut off the pressure bleeds off almost immediately, leading to the pressure building in the first consern. Normal?

Schurkey

1. It would be wonderful if you'd tell us WHAT VEHICLE THIS IS.

2. First guess: Defective fuel pump relay, or defective wiring for the fuel pump relay. Fuel pump does not activate based on ECM command to fuel pump relay, pump finally activates when oil pressure closes the oil pressure switch, bypassing the fuel pump relay. Complete diagnostics are in the service manual for whatever vehicle this turns out to be.

IF (big IF) the pump is failing, maybe all it can produce is 12 psi. Faulty wiring to or from the pump (reducing voltage) could lower pump pressure; as would a failed pump. In the end, if the regulator is set for 12 psi, that's what you're going to see on the gauge unless the pump can't produce that much.

I don't think early TBI (perhaps ALL TBI) systems retain pressure. Check the service manual for your vehicle.

rsc350

My apologies, I was in the mind set that the thirdgen boards under TBI was specific enough. It is the 92 RS with a 350 as stated in my sig. I'll try to be more specific in the future.

I would find it hard to believe (although I did not state it in the post but instead in the title, or tried to imply), the brand new TPI pump that I literally just put in the vehicle has failed.

I did find an issue which was not immediately indicated. Upon opening the file in tunerpro many of the tables are way off due to a faulty USB-Serial cable when reading out of the EBL and then writing it back in. My hope is that this faulty bin file was causeing the injectors to stay open longer than intended, if not constantly, showing an incorrect fuel pressure.

Correct me if I am wrong, but I should be able to get a semi-accurate fuel pressure (maybe slightly high) by taking the ECM control away completely and bypassing the relay by jumpering the orange and grey wires (same to pump the tank empty to drop it), this should flow fuel to the regulator (and guage) and 100% of the fuel back through the return but still give a pressure reading allowing me to wrap up the fuel tank project prior to sorting out the bin issues and rule out that the pump is not bad?

Schurkey

Did you ever test the voltage at/near the fuel pump WITH THE PUMP RUNNING?

Both of my Luminas have similar voltage problems: About one volt lost on the "hot" side, due to undersized wire as built by GM. Have traced "hot" wires back to the power stud near the battery, there are no bad connections--the voltage drop is EVERYWHERE. Wire is 16 gauge, on-line calculators for amperage draw and length of wire suggest that it should be 12-gauge.

There is more voltage drop on the ground side--about the same 1 volt as the "hot" wiring. Pump therefore gets ~12 volts when engine is running, but it should have nearly the same voltage as the alternator produces--14.2. Both cars run well enough, and fuel pressure meets specs--but there's no margin for error any more with the pump running on poor voltage.

Can't help you there.

Bypassing the relay would give you a reasonably-accurate fuel pressure reading. IF the relay and relay wire connections is a source of voltage drop on your vehicle, you may still have low pressure depending on how the bypass is wired. On my Lumina, the bypass negates the magnetic coil, but still uses a set of contacts IN the relay; if those are burned, there could still be problems.

Point is, the "fuel pump" is both an electric motor and a hydraulic pump; if EITHER the motor or the pump is unhappy, fuel pressure and fuel volume can be affected.



Did you ever figure out why the pump doesn't run for two seconds when the ignition is turned "on"? You need to investigate that fuel pump relay and associated wiring.



First Guess: the wiring has some voltage drop, the pump isn't getting the voltage it should--but the real cause of your 12 psi is "that's what the pressure regulator is set to".