LS1 fuel pump prime intermittent
 

My 72' has a LS1 swap with a fuel pump priming problem.
On occasion after driving for a while and switching the engine off for a while it will not start. It turns over fine but I don't hear the usual fuel pump priming that I get when switching the key on.
This has happened on thee occasions. After towing the truck home and letting it sit for a while it starts just fine.
I thought it might be wiring to the fuel pump and I checked it all. I found one questionable connection and fixed it, but I guess that wasn't the real problem because it happened again.

Re: LS1 fuel pump prime intermittent
 

It could be many things , most use a relay to their fuel pump , that would be 1 suspect , the pump itself another , the trigger wire from the pcm another [ but realize the computer shuts the pump off when adequate pressure is in the fuel rail or the key is on for awhile and the engine is not running . ls1tech.com and the ls section on the board may hold more guesses to your issue , post your results

Details on your pump and tank choices , and return - pressure regulator details will help in a diagnosis

Re: LS1 fuel pump prime intermittent
 

Thanks for the reply, I'm new to the LS game. The fuel pump seems to run fine once the engine is running, so I don't really suspect that. I believe you are correct in the #1 suspect being the relay. I have no idea where that is but I'll find it. Whats the best way to test it?

Re: LS1 fuel pump prime intermittent
 

Whose LS wiring harness do you have? Once you find the relay, I would just install a new one.

Re: LS1 fuel pump prime intermittent
 

Painless wiring harness.

Re: LS1 fuel pump prime intermittent
 

Their instructions should point you to the relay. I would go with a new 50 Amp relay when you replace it, just for added protection. What fuel pump are you running?

Re: LS1 fuel pump prime intermittent
 

Sorry I'm not real quick with the answer of what fuel pump I'm using. I didn't do the original install and I'm out of town right now.
Is it possible that the computer is not sensing low fuel pressure. Therefore not priming the fuel pump? If so is there a sensor I should check?

Re: LS1 fuel pump prime intermittent
 

I'm pretty sure there is no sensor on your swap that tells the computer to not prime the system. It's usually done based on time (at least Gen III motors are). Something else is going on with yours that is not allowing the pump to activate. I would replace the relay first and see if it happens again. If it does, more than likely you have something going on with the pump. Could be that the pump is getting hot by time you stop driving, and then cools down after you let it sit.

Re: LS1 fuel pump prime intermittent
 

Also, you should repost your question here:

http://67-72chevytrucks.com/vboard/f...play.php?f=206

Re: LS1 fuel pump prime intermittent
 

Thanks for all the help guys. I'll try the relay and if I continue to have problems I'll repost in the correct place.