Fuel pressure problem

[84delta]

All right need some ideas. My fuel guage stopped working on my ls swapped 80 malibu because the sender went bad. Replaced the sender fuel guage works but now I'm have a fuel pressure issue. At idle and light cruise I sit around 44-48 psi then even under medium/light load pressure drops quickly. Down to single digits and goes lean under heavy load. I did run the pump dry a couple times so thought maybe I hurt it so replaced it with a different walboro 225 I had lying around. Same result. Pulled the tank did continuity checks and all checked out. Put a new strainer, tank is spotless, back washed the 10 micron filter clean as a whistle and tried a run with it bypassed, blew out the feed lines with compressed air, even threw a new pressure regulator at it nothing. added a second thicker ground today just to be safe. Anythoughts or ideas? Car ran flawlessly before replacing with an identical sender.

 

[Tony1968]

Have you tried to take line right from the tank/pump and put a gauge right there? Also a new pump doesn't mean it's a good one. I've been there

 

[64nailhead]

Verify voltage at the pump, and then pull the supply line and verify flow rate.

Assuming this is a return system, verify return line is easily blown through.

 

[84delta]

Verify voltage at the pump, and then pull the supply line and verify flow rate.

Assuming this is a return system, verify return line is easily blown through.

 

[84delta]

So I think I've narrowed it down to the pump not getting enough power while underload. Blew threw the lines no restrictions. Psi is good at idle. I added an external regulator after the fuel rail in the return line to accompany the stock regulator and same result. I'm going to modify a new sender with a bulkhead fitting and 10 guage power and ground directly to the pump instead of using the crappy wiring that came with the sender. I don't have a way to test amperage load/draw while under load but I suspect it's my issue. Tried 3 factory regulators 2 used 1 new. Blew the lines out. New inline filter and pump sock.

 

[64nailhead]

There are some stupid tests that you can do to verify if voltage drop is an issue.

Describe your system - stock sender and pickup? How is the pump attached to the piping? It could be leaking inside the tank and as soon as you need flow the leak overcomes the pressure.

I mentioned testing the free flow of the pump. You can also check this on the return side of the system and have an air pressure regulator piped to the regulator and put 25-30 psi on it. The return fuel increase should be obvious in terms of volume and pressure.

Any pics of the pickup or the system?

 

[84delta]

There are some stupid tests that you can do to verify if voltage drop is an issue.

Describe your system - stock sender and pickup? How is the pump attached to the piping? It could be leaking inside the tank and as soon as you need flow the leak overcomes the pressure.

I mentioned testing the free flow of the pump. You can also check this on the return side of the system and have an air pressure regulator piped to the regulator and put 25-30 psi on it. The return fuel increase should be obvious in terms of volume and pressure.

Any pics of the pickup or the system?

 

[84delta]

It's the factory 01 5.3 return style rails going into the factory 5/16 hardliners then rubber to the tank. I did put a pressure guage into the return line right after the rail and reads the same as my holley pressure sensor to the ecu. Well close enough. I did swap pumps and when I did so used a new section of hose to attach it to the sender. I don't feel like it is pushing passed the pickup but I could be wrong.

 

[64nailhead]

Doesn't look it.

You mentioned 44-48 at idle. 44 is low on a 58psi base system, even with a stock cam. 50 should be the lowest. What cam are you running? The bogger the cam, then the closer to 58 it should be (less vacuum).

 

[84delta]

Doesn't look it.

You mentioned 44-48 at idle. 44 is low on a 58psi base system, even with a stock cam. 50 should be the lowest. What cam are you running? The bogger the cam, then the closer to 58 it should be (less vacuum).

Sloppy stage 2 turbo cam. It's very mild. Also when I threw the external fuel pressure regulator in the return right after the rail I dialed it into between 58 and 60 psi and still no go.