blownmiata

We cranked the LS1 for the first time today. Ignition turns the engine fine but no fuel pressure. Orange is hot and pink is switched. The green LS1 fuel trigger wire has 12V ignition power to the fuel relay trigger wire of the car, but the fuel pump doesn't run.

However, when I was checking for trigger wire power, the pump runs when I touch the test light to the trigger wire! Bad ground? The battery is grounded to the frame, and frame to the engine. I also hooked up the one ground wire from the LS1's PCM. What should I check next?

blownmiata

Looking at the schematic again, it appears that the LS1 fuel trigger wire must ground the relay, not power it. Now it makes sense why putting the test light on the trigger wire makes the fuel pump run. However it doesn't answer why the LS1 computer isn't closing the relay. We do not appear to have spark either. Could this be the theft deterrent system (VATS?)?

stealth71

iTrader: (15)

I was just doing some reading on fuel pump wiring and the signal wire coming from the PCM, C2 Red Pin 9 is the Fuel pump signal. This wire provides 12+ to turn on the fuel pump relay.

blownmiata

Yep, thats right - the LS1 PCM sends a 12V+ signal to the trigger wire. Unfortunately my host car closes a switch to ground to activate the fuel pump relay - totally opposite. I rewired the car's normal trigger wire to ground, and the LS1 trigger wire to one of the hot leads for the relay solenoid, and now it works fine. Thanks!

stealth71

iTrader: (15)

Glad you got it figured out.