Can someone tell me what this part is and its exact function please. I replaced the sending unit in my camaro tbi and initially after everything was reassembled the car was running fine and fuel pressure was at 10, but then I had an issue with fuel pressure and it sounded like gas was pouring back in the tank. I removed the sending unit and noticed that, what looks to be a return check valve, had broke off and was sitting in the tank. I tried to reattach it, but it seems that my fuel pressure reading is pegging the fuel gage that goes to 15psi at the tbi. I am assuming this Is a return line check valve to help control pressure? I am pretty sure I am going to have replace the entire sending unit again because of that piece.

 

[QUOTE=camarorsssss;6565800] Can someone tell me what this part is and its exact function please. I replaced the sending unit in my camaro tbi and initially after everything was reassembled the car was running fine and fuel pressure was at 10, but then I had an issue with fuel pressure and it sounded like gas was pouring back in the tank. I removed the sending unit and noticed that, what looks to be a return check valve, had broken off and was sitting in the tank. I tried to reattach it, but it seems that my fuel pressure reading is pegging the fuel gage that goes to 15psi at the tbi. I am assuming this Is a return line check valve to help control pressure? I am pretty sure I am going to have replace the entire sending unit again because of that piece.

It would seem that that valve is a roll over/pressure relief valve based on further research. I guess my question now would be, would that cause the fuel pressure to increase? I am thinking maybe the gage I have at the throttle body had gone bad possibly, since it is probably 15 yrs old and not liquid filled. I have checked all the lines and do not see any damage or kinks along the routing or at the tank. I also have a leaky injector now, looks to be at the larger O-ring at the top of the injector. If I do have pressure reading over 15psi, I do not know what it actually is because the gauge only goes to 15, what else could cause that. I want to reiterate that when I first swapped the pump for TPI pump and sending unit and turned the car on, I was able to let it idle and get to temp and maintain 10 psi of fuel pressure.

 

Changed out the pressure gauge, still the same thing, very high fuel pressure that doesn't seem to leak down. I changed the regulator diaphragm on the TBI, no change.

It is the original tank and I did inadvertently run it empty because the fuel gauge wasn't working, possibly sucked up some debris and clogged something?

Here is what I am thinking is left at this point:
Clogged, obstructed return line
The broken (repaired?) roll over/return check valve is no good, not sure if this would cause a high fuel pressure though.
I am pretty sure none of my fuel lines are swapped when I changed out the sending unit, but I can check again.

Does ECM have anything to do with commanding fuel pressure?

 

Have you pulled the return line and blow compressed air through it with the fuel cap removed?

 

I have not yet, that was going to be my next step. Should I be removing the return line at the TBI and blowing the compressed air back towards the tank? How much PSI should i use?

Is it possible the new fuel pump is just putting out too much pressure? I ordered a TPI pump but who knows if it is actually what i ordered?

 

Quick update: After spending the entire evening going through everything and trying to determine where things were wrong I believe I have solved it. Of course it seems to have been something stupid and simple, as it usually is. I blew out all the fuel lines to confirm no debris or blockages, the return line was in fact dirty and the rubber line in the engine bay was a little kinked, but not terribly so. I made sure to confirm everything was clean and the TBI itself was cleaned. After putting everything back together I cycled the ignition to confirm proper fuel pressure and yep fuel pressure right around 12. I think great, ok we got this thing fixed, go to start the car and it runs for a few seconds and then I start to notice the injectors struggling to fire and spit fuel. Hmmm WTF. I go and check my connections at my VATS delete box and all seems good there and then I check my battery connections to confirm good voltage and well the positive battery cable was not tight, but it was because the screw was partially stripped now. Ok, so I fix the positive battery cable and think ok we are now good to go. NOPE, same thing, notice on the gauge no fuel pressure now and injectors not firing. UGH, ok lets go back and re check everything at the fuel pump and confirm no leaks. No leaks, so I say to myself, lets disconnect some fuel lines and see what has fuel and what doesn't, because i am suspecting the check valve and return line are cris crossed. This is all because the previous owner did a hack job of the lines and cut them all at the fuel sender outside the tank and I had to deal with it when I put in the new pump and sender. My answer to confirm which is the return line is to leave the two lines I am not sure of disconnected from the sender unit and cycle the pump to determine which one spits fuel. Well, I got my answer, the return line and check valve line were interchanged, thus creating a lack of return fuel to the tank once the initial spurt of fuel was delivered, which seems to make sense with having 12 psi at first and then nothing. I will confirm everything tomorrow but I am pretty confident the issue is resolved. Lets hope!