I Have a 1991 coupe. several weeks ago the fuel tank level indication quit working' After a little troubleshooting, I determined the level meter in the fuel tank was bad. I found a brand new GM NOS tank meter assembly which was still in the original box and included the pump and anti flow surge device. I replaced the unit. Turned on the key and sure enough. I had fuel level indication.
However, the car would not start. I figured, "Air in the lines" Right? After a long search, I found a way to make the pump run long enough to purge the system. I went and bought a "Fuel Pressure test gague". I jumpered to run the fuel pump and bled fuel off the fuel rail schrader valve until no more bubbles. I had about 12 PSI. Of course the car still would not start. So I went and bought an inline fuel filter and replaced the one on the car. I had about 8 psi. Pulled the tank assembly inspected it and adjusted the intake screen, but everything looked as it should. Reassembled and ran with about 6 psi, disconnected the fuel lines at the pump outlet and the inline filter. Blew air back line from inline filter to pump. Did not appear to be restricted. removed tank assembly once again and replaced new fuel pump. reassembeled and now have about 2 PSI. I seem to have good flow, just no pressure. This is with the fuel pressure regulator blocked (hose pinched). WTH is going on???

 

Test it with your old known working pump.

 

Did that. No change.

 

I suspect that a line inside the tank is losing pressure...probably a pulsator clamp is loose.

Really, here are the options for your condition;

1. Bad regulator (can't be, you've pinched the return line off).
2. 2 bad pumps (possible, but unlikely)
3. A restriction (clog) on the pressure side (suddenly?)
4. 8 suddenly leaking injectors (one in a trillion odds)
5. Electrical failure (I'm assuming you didn't wire the new pump backwards, correct?)
6. Pressure is bleeding off inside the tank. (the most likely explanation).


You have flow, just not adequate pressure. This means one of two things....insufficient flow, or insufficient restriction to build pressure. Your restriction didn't suddenly change, so what did? Flow into the pressure line is the answer.

Double check your clamps on the pulsator. Also check for any obstruction in the sock.

 

No offense, but you're positive that you're pinching off the RETURN line, correct? Not questioning your skills....but I've done sillier things than that before...

 

Sorry about the delayed respone. I had to go to work.

I replaced the Pulse damper with another new one. Pump is wired factory. Plus, I tried the new pump and the old pump with same results. When I was replacing the in-line filter under the car, I applied power to the pump and was able to fill a 2 leter bottle in 1 minute give or take a few seconds. That should be about right for a factory (135 lph) pump. After tightening the filter connections, still only had abot 6 or 8 psi. What you say makes since. It has to be loosing pressure in the tank. The return is not only pinched, but it is disconnected at the tank and any flow would be pouring down the driveway.

Thanks Guy!