Question on LS engine fuel pressure

[rickpaw]

Hi guys,

I got the engine running on my car the other day, and according to the fuel pressure gauge, the fuel pressure is low. Quick specs:
-5.3l/4l60e combo drop out from a 01 Chev pickup. Running LS1 intake/injectors/ECM. Truck coils. Otherwise bone stock. ECM/harness from PSI.
-Fuel system consists of Tanks Inc FI tank, Aeromotive 340 pump, Wix C5 reg/filter near tank, Finch's dual tank vent. 3/8 hard lines with -6 an lines going to the rails/fuel pump.
-Mechanical fuel pressure guage mounted inline prior to fuel rail inlet.

The issues:
-1) The fuel pressure seem to be low, around 40 psi at idle. Idle speed 600 rpm. It's my understanding that LS engines won't run or run poorly with pressure less than 58 psi. I checked for voltage at the pump, and it's getting 13.5V. Alternator puts out a bit over 14V. Fuel pump is wired thru a relay, with 10 gauge power/ground wires. Engine runs fine though, with no codes showing. I checked for blockage at the pump inlet (none), all the hose connections at the pump are tight. Do you think the gauge maybe bad and showing inaccurate reading? It's a cheap oil filled mechanical gauge I bought from amazon.
-2) Fuel pressure drops to zero after shut down, and I have to let the pump run a bit (2-3s) to prime the system back up. Is this normal, or do I have to use some sort of a check valve?

Thanks for the help/inputs.

[cornfedbill]

I would check with another gage before making any changes. Do you still have the shrader valve on the rail so you can check the pressure?

40 psi would be enough to run the engine at idle. It will just have to compensate when in closed loop. You will only have real issues at high load.

What type of pressure regulator are you using?

[CarlC]

I agree with Bill. Verify the gauge reading first. The basic fuel system you have is way more than what is needed so it's not a volume capability problem.

[rickpaw]

I'll check fuel pressure at the schrader valve. I suspect it's the gauge, since it's a cheapo one on Amazon.

I'm using Wix C5 Corvette regulator/filter.

I'll post what I find this weekend. thanks for the tips so far.

[rickpaw]

What about pressure drops to zero when the pump is turned off. Shouldn't it be some residual pressure remain in the line?

[MrForce]

What about pressure drops to zero when the pump is turned off. Shouldn't it be some residual pressure remain in the line?

Not unless the fuel pump has a check valve.

Rob

[68EFIvert]

I had some issues on my car recently with the fuel system depressurizing. The car was hard to start until I added a check valve after my aeromotive a1000 pump. The guys at aeromotive said that my pump finally has enough use that it has loosened up and the pressure from the rails reverses the pump and depressurization the system as soon as the key is turned off. The check valve fixed my problem.

[rickpaw]

False alarm. The gauge I have is bad, as in showing low pressure. I bought a gauge that connects to the schreader valve at the end of the fuel rail, and it showed a steady 56 psi @ idle.

Darreld, I saw your post about loosing fuel pressure. I will add a check valve down the road, as I'm behind schedule on my swap. Need to get it running for cruising the coast in Oct. I thought the Aeromotive 340 pump has a built in check valve?

Now time to chase some transmission codes that popped up. LOL.

[cornfedbill]

Glad it all worked out.

[rickpaw]

Glad it all worked out.

So am I. I'm trying to get this swap done prior to cruisin the coast, so I started sweating on stuff that did not work, and overlooked the simplest things. Now I just have to find a decent gauge to replace what's on there now.

Tu