Stalling after replacing fuel pump

[kdonn]

I just replaced the fuel pump in my dad's '96 Q45 and now it is stalling randomly upon starting. If I give it a little gas it will start fine, idle fine and drive fine. But 8 times out of 10 if I just turn the key it will fire up but stall right away. Any suggestions? I'll list below what lead up to this point.

I've done the fuel pump on a previous q45 successfully(thanks to this forum). This time around I noticed the humming from the trunk and decided to replace the pump though vehicle was running fine with no issues. I installed a new pump with a new o-ring and new fuel pick up sock. After installation the gas gauge was not registering but the car was running fine. The following weekend I pulled the pump again to see that the gas level indicator was knocked off when I put the pump back in. So I reinstalled now the gauge works fine but I have the stalling issue. One thing I noticed is that the O-ring seems too large in diameter (like it expanded after being installed for a week) After a bit of maneuvering I was able to get the o-ring to fit but there maybe a slim chance there is a gap.

I've done the searches and read the threads. Any suggestions would be appreciated.

[Q45tech]

Measure the fuel rail pressure for 10 minutes after shutdown and the cranking and short term to run.....................very accurately in second increments.

Pressure may be bleeding down too fast and not meet the 20 psi prior to start.

[goody90q45]

.......I was able to get the o-ring to fit but there maybe a slim chance there is a gap.......

If there was a gap you'd know it since there would be an intolerable smell of gas in the passenger cabin as you drove.
Are the fuel pump connections inside the tank tight? Is there any scorching on the FPCU socket or connector possibly pointing to a bad FPCU?

[kdonn]

Measure the fuel rail pressure for 10 minutes after shutdown and the cranking and short term to run.....................very accurately in second increments.

Pressure may be bleeding down too fast and not meet the 20 psi prior to start.

I'll go to work on measuring the fuel pressure.

.......I was able to get the o-ring to fit but there maybe a slim chance there is a gap.......

If there was a gap you'd know it since there would be an intolerable smell of gas in the passenger cabin as you drove.
Are the fuel pump connections inside the tank tight? Is there any scorching on the FPCU socket or connector possibly pointing to a bad FPCU?

No fuel smell. I'm going to get a new o-ring and pull the pump to look at the connections. I may have loosened some connections getting the pump back into the tank. i'll also take a look at the FPCU for scorching.

Thanks for the input. I'll post results.

[kdonn]

OK. I think I may have solved this problem. I stopped by the dealership and picked up a new o-ring. The one on my car is about 3 weeks old. I set them side by side and the older one is thicker and larger in diameter. It was not fitting in the grove on the tank. The first day I installed it it fit fine. Going back in a week later it had expanded and would not fit properly. I took a picture of the o-rings together but was not able to post. Anyway I intsalled the new o-ring and it is now running fine. It appears that the problem is solved for now.

Thanks to all.