With my fuel pump relay controlled by the pcm ('00 fbody pcm, '05 gto fuel pump), my fuel pump runs continuously when the ignition is turned on. It does not come on for 2 seconds and shut off.

I do not have any fuel in the tank. Does this make a difference? I thought the 2 second on-time was controlled by wether or not the pcm sees a crank signal. I dont have a fuel pressor sensor of any kind.

Any ideas?

 

Is your pump wired like this?

 

Yes sir. Im using a relay box from Current Performance. The pcm fuel pump request goes to the relay, the other side of the relay receives batt power, and the grounds are correct.

Im wondering if it has to do with no fuel in the tank, but that doesnt make much sense being there is no way for the pcm to know there is fuel pressure.

 

If you continue "testing" the system without fuel in the tank, be prepared to buy another pump....

 

I understand that. Which is why I havent let it run for more than 5 seconds. Ive since pulled the relay so I can test the other ignition systems w/o the pump running.

 

just a guess and maybe to double check.. are you sure your fuel pump activation is coming from C2 (Red) pin #9 ?.. if it is just a hot pin when the IGN turns on. That would explain the relay staying hot and not turning off after 2 sec....

Just something to check.

what is keeping you from adding some gas to the tank !?

 

I'll have to check it again. I checked and rechecked everything when I was building the harness, but I'll check it out once more.

I have a few other things to take care of before letting it run.

 

Problem solved.

Added fuel to the tank...now it runs for 2 seconds and shuts off. Magic.

 

That simple of a fix. ! LOL...

 

Why does this happen? When testing my engine on the stand I noticed the fuel pump relay signal(pin 9) stayed at 12v when I had the "key on" wires connected. I was expecting 12v for 2-3 seconds. Now I'm finishing up the under dash wiring and decided to test it again with the "key on" again it stays ay 12v. This is testing directly to pin 9 with no relay or pump connected. Does/Can the PCM really detect fuel pressure?

THANKS!,
Jay

 

May have something to do with the position of the float.

 

I hope not because I'm not even using the stock float. I wouldn't think so though. I should have my pump in tomorrow. I'll check back in with my results.

 

GM built it into their PCM logic so it would deter wives/girlfriends from running the tank dry. The pump runs continuously when they leave the ignition on/no gas, kills the pump, pisses us off, makes the General some money (new parts and/or labor), and teaches them a lesson. It says so in the Master Tech handbook.

 

Wouldn't stop my gf, everytime I get in her car the low fuel light is on!

And to the OP, if putting fuel in it fixed the problem, it was purely coincidental. The PCM doesn't care how much gas is in the tank.

 

It does not, Im using the original float for the '63 tank. The float on the GTO sender has been removed and the only wires going to it are the fuel pump power and ground.

Im thinking it has something to do with a current draw, fluid vs no fluid.

??

 

I thought about current draw also, but with it going through the relay it shouldn't take much draw. I think you may be right though.

 

It has nothing to do with current draw, it's set in the PCM to turn on for a couple of seconds, and if no RPM is detected it turns off. Even with no fuel pump hooked up, the relay should come on and go off within a few seconds.

 

OK, that's what I expected. So, why would my(and the OP's)pin 9 stay hot? The engine ran fine on the stand. I'll have the pump wired up in a couple days. Hopefully the problem will magically cure itself for me too. If it doesn't I'll just run the FP 12v through an oil pressure sw.

Some info just for reference:
2003 5.3
Modified stock harness
Wait4Me tune

 

I think you will be just fine.

I understand that the pcm will shut off the pump when it sees no crank signal after 2 seconds, but that doesnt explain why mine and 67swb had the same thing happen.

BTW, ls1nova71, I believe I saw your car at the Goodguys autocross in Des Moines 2 years ago, very cool

 

I ran across this thread during my search last night. I, too, have experienced this same issue. I wired everything up as it should be to test the PCM (as well as my ODB II and HP Tuners). I expected the pin to pull to +12v for 2 seconds and then stop. However, my DVM showed that it was pulling +12v continuously. The fuel pump was not wired up, I merely connected my DVM to the pin.

At the time my intake was off as were most of the top sensors save for the cam position sensor. I spent a couple hours perusing here and Google in general for an answer to this phenomenom.