I'm working on a LS1 conversion into a RX7, and I'm using the PCM to turn on the fuel pump relay. The engine cranks for about 2 seconds, then the PCM shuts off the fuel pump relay and the engine dies. If I turn on the fuel pump relay without the PCM by supplying power to the turn on lead directly from the battery, the engine starts up fine. So I'm wondering what's making the PCM turn off the fuel pump in 2 seconds?

I've heard that if the PCM does not sense that the engine has started within 2 seconds, it shuts off the fuel pump. So is it possible that I have a bad crank position sensor that's not telling the PCM that the engine has started? How do I check if the CKP sensor is good?

Thanks!

 

You wired the power to the fuel pump relay wrong. You have it so there is power while in the RUN position but not in CRANK position. Check your power wires.

 

Power to the fuel pump relay is directly from the battery, then to the fuel pump. I am certain that it's the PCM turn on lead not providing 12V to the relay after the engine has started.

 

What year engine?
What harness?
What PCM?

Do you know wiring?

 

Could be a vats issue

 

I'm using a 2002 LS1 from a Camaro, stock harness and stock PCM from the same car. I paid someone to modify the harness for me for this conversion, so I only have to connect the wires, and they're labelled correctly. Since the engine starts and runs fine when I turned on the fuel pump relay directly, I don't think it's the VATS, as the VATS will turn off the fuel injectors.

For some reason everything works now! I didn't do anything between last night and today, so maybe I just needed to let the battery charge longer, or prime the fuel pump for a little longer. I'll post if the problem arises again, thanks for your help!

 

Good Deal.