PBChase

I am usually in the C1/C2 forums but need your help. I am just finishing installing a new LS3 GM Crate Engine in a 1959 Corvette. I am also using a new GM ECM/Harness that works for the LS3. Everything is wired but when I turn the ignition switch to "on" the in tank fuel pump does not cycle on for two seconds like it should. I know that the fuel pump works because it turns on when I bring 12 volts directly from the battery. I know there is power to the fuse relay center because when the ignition switch is turned to "on", the MIL light goes on. I have checked the 30A fuse for the fuel pump and it is okay. I will swap out the fuel pump relay just in case it is bad but I doubt it as everything is brand new. I have checked the wire from the ECM to the fuel pump and there is nothing wrong with it. From what I have read so far, when the ignition switch is turned to "on", the fuse relay center sends a 12 volt signal to the fuel pump relay that powers the fuel pump circuit for two seconds. The relay closes and then waits for a crank signal which will trigger it to open again.

Any help on what is going on would be very much appreciated.

Thanks, Peter Chase

KENS80V

I would check the wire pin assignments in the three ECM connectors and relay/fuse box. When building the harness they have been known to accidentally miss place the pins.

We even had one unlucky forum member (gt40s.com) who bought a crate LSA engine and found a 24x reluctor wheel on the crank.

PBChase

I will check this out in the morning. Thanks for the response.

Peter

KENS80V

The ECM harness connector 1 (blue) has the fuel pump relay control wire at position #13. You can check that wire to see if it delivers 12volts to the fuel pump relay for those 2 seconds.

Here is a wiring schematic (PAGE 9) that helps to show how the fuel pump circuit works. The GMPP harness previously used the early CTS V for the operating circuit. These schematics are from that car.

http://www.revbase.com/BBBMotor/Wd/D...dPdf?id=135577

Also check/trace the ground wire of that same circuit (from the relay to ground). Without the needed ground connection the relay will never energize and provide the current to the pump.

There should have been 3 separate grounds from the harness to the engine block.

Dial In Corvette

You will likely want to ensure the computer is getting the correct fuel level reading. If the reading is(for instance) too low, the ecm would likely not fire the fuel pump or the injectors. It is expecting to see a specific reading range. You will want to determine the range and make sure the correct terminal is seeing the correct reading. Years ago I was able to do this with a resistor. Don't remember exact details.

Good luck.

wolfk

Found this thread via google, I have the same exact problem as OP. I hope he sees this and responds to whatever the solution was.

wolfk

Well, found the problem, loose harness ground connection at rear of engine block. This is ground source for fuel pump and ignition relays.