LPFP Pressure decreases as car warms up

[Ls3]

Hey folks, I'm in the process of diagnosing my why bank 1 LTFT can range from 10% to 20% higher than bank 2 and ends up triggering a shadow 29E0 fuel mixture code which eventually becomes an active fault. I guess that's a story for another time.

I've replaced the LPFP while trying to track down this issue. I replaced it with an OEM Continental unit and am seeing the LPFP pressure slowly go down as the car warms up. On a cold start in the morning it will start at 72~ psi, after 15 minutes of driving it'll sit at 65~ psi, and after an hour or so of highway speeds it'll be at around 55 psi. On restart the pressure goes back to what the warm pressure was. Is this normal or should I be looking at the EKP or fuel pressure regulator on the other side of the tank? I'm guessing the old fuel pump was still good since it displayed the same behavior.

Thanks for any insight you all could provide.

 

[martymil]

lpfp pressure issue sounds like the intank pressure regulator is having an issue.

 

[Ls3]

Ha, I replaced the filter/FPR and now the pressure is even lower.

 

[martymil]

Check all your in tank lines one of them must be loose or your pump could be stuffed.

The only other things that could be is the lpfp sensor or ekp which I highly doubt.

There is nothing else the system is pretty basic.

 

[Ls3]

Pulled everything, no kinked lines or leaks that I can see. Would hope a new pump and new regulator wouldn’t be defective. HPFP rail pressure looks okay at idle and under load. Wondering if it’s the lpfp sensor.

 

[martymil]

Hpfp rail won't be effected until the lpfp starts to go below 50 psi or less.

 

[Ls3]

Ended up being the the LPFP sensor!

 

[martymil]

Thats good to hear, for anyone in the future chasing this type of problem this is a good thread to see.

There are only few things that could go wrong.

Fuel pump
The intank regulator
Lpfp Sensor.
One of the lines has come off or the clamps are leaking.
EKP if its overheating with a large LPFP pump.

The system is very basic.

 

[Nighthawk]

Thats good to hear, for anyone in the future chasing this type of problem this is a good thread to see.

There are only few things that could go wrong.

Fuel pump
The intank regulator
Lpfp Sensor.
One of the lines has come off or the clamps are leaking.
EKP if its overheating with a large LPFP pump.

The system is very basic.

Thanks for this post guys, it helped me mucho, I solved my erratic fuel pressure issue with a new low pressure sensor