LS Fuel Pressure

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custodian

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I installed a fuel pressure gauge on the 5.3LS in the 73 C10 at the pressure test port. I currently have an external Walbro fuel pump. When I turn the key on, the gauge reads right at 58/59 psi. When I crank it, it reads over 100 psi. Any thoughts?
 

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what regulator are you using?
 

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Has this engine been running? Why did you decide to test the psi? Is the regulator vacuum referenced?
 

custodian

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Has this engine been running? Why did you decide to test the psi? Is the regulator vacuum referenced?
Motor has been running very good, have been getting PO codes for rich mixture, regulator is vacuum referenced. Just checking out all possible causes.
 

SquareRoot

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Being vacuum referenced the psi should drop below the setpoint at idle and gradually rise to the setpoint under load. I wouldn't worry about what it is during cranking. Check it at ide with the vacuum hose connected and disconnected. Those are the two that matter. If indeed, it's pushing 100 psi that will explain why its running rich. There is only 2 variable in the fuel equation, duration and pressure. Duration is programming, pressure is manual, i.e., fuel pump/regulator/return system.
 

custodian

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Being vacuum referenced the psi should drop below the setpoint at idle and gradually rise to the setpoint under load. I wouldn't worry about what it is during cranking. Check it at ide with the vacuum hose connected and disconnected. Those are the two that matter. If indeed, it's pushing 100 psi that will explain why its running rich. There is only 2 variable in the fuel equation, duration and pressure. Duration is programming, pressure is manual, i.e., fuel pump/regulator/return system.
PSI stays above 100 when running with the vacuum line to the regulator hooked up or removed. The fuel system is the stock 2002 Silverado with fuel return line.
 

Bextreme04

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Motor has been running very good, have been getting PO codes for rich mixture, regulator is vacuum referenced. Just checking out all possible causes.
That's the same regulator that is on the 7.4L L29 motors. Its a piece of junk. I would suggest getting a blockoff plate from ICTbillet and run an adjustable aftermarket one.
 

SquareRoot

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I'm with Eric. That's a junk regulator. I use an "authentic" Aeromotive and I love it. Avoid the Chinese knockoffs on fleabay and scamazon!
I would imagine your plugs are a little dark?
 

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That's the same regulator that is on the 7.4L L29 motors. Its a piece of junk. I would suggest getting a blockoff plate from ICTbillet and run an adjustable aftermarket one.
Tell me more about this knockoff plate? Curious how this mounts, I'm not familiar with OEM LS stuff.
Wait, nevermind, I was being lazy, I just googled a Youtube and there it was. lol
 

custodian

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Being vacuum referenced the psi should drop below the setpoint at idle and gradually rise to the setpoint under load. I wouldn't worry about what it is during cranking. Check it at ide with the vacuum hose connected and disconnected. Those are the two that matter. If indeed, it's pushing 100 psi that will explain why its running rich. There is only 2 variable in the fuel equation, duration and pressure. Duration is programming, pressure is manual, i.e., fuel pump/regulator/return system.
Uhmm, return system. If I remember right, I used the stock 73 sending unit with two outlets. Could that have an effect with the LS fuel return?
 

custodian

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I'm with Eric. That's a junk regulator. I use an "authentic" Aeromotive and I love it. Avoid the Chinese knockoffs on fleabay and scamazon!
I would imagine your plugs are a little dark?
Thought about adding an adjustable fuel regulator.
 

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Browse the attached from Aeromotive. It explains it very well.
 

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SquareRoot

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Uhmm, return system. If I remember right, I used the stock 73 sending unit with two outlets. Could that have an effect with the LS fuel return?
Do you have a return style system? Assuming yes, you should have a feed line no smaller than 3/8ths from the sending unit pickup to an inline filter and then into your pump. Between your pump and fuel rail should be a finer mesh, high pressure filter. On the outlet side of the fuel rail should be the pressure regulator and a minimum 5/16th return line back to the tank. Any bigger difference between the feed & return lines is a restriction and will cause your pressure to be higher.
 

custodian

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5.3 LS, 350
Do you have a return style system? Assuming yes, you should have a feed line no smaller than 3/8ths from the sending unit pickup to an inline filter and then into your pump. Between your pump and fuel rail should be a finer mesh, high pressure filter. On the outlet side of the fuel rail should be the pressure regulator and a minimum 5/16th return line back to the tank. Any bigger difference between the feed & return lines is a restriction and will cause your pressure to be higher.
Yes, return style system, 3/8" inlet fuel line with filters, 5/16" return line back to the tank.
 

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