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Fuel pressure for LS:

sweetk30

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depends on if 1 or 2 line system

some early were on the rail for the regulator and cars tended to be on the fuel filter . but then they went in tank on the sender .

need more info / specs or pics to tell you 100% what you need .
 

vandelay industries

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i was asking in general.

Let's say an LS3 crate engine.

Actually, why don't we just discuss both types of systems----both return and returnless.
 

sweetk30

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already told you the info in general above .

but i was asking for pics and info IF YOU ALREADY had one and didnt know .

so there should be required info on a crate engine for whats needed and or included to help figure it out .

but a ls3 is a car based ls engine so it should be returnless and will prob need the fuel filter / regulator setup or intank sender / regulator unit .
 

vandelay industries

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shady

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I still gotta buy one of those myself.
 

vandelay industries

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i guess what i'm trying to get at here is, the computer does not know or care what the fuel pressure is? : Because it doesn't monitor fuel pressure(?) That is taken care of by a mechanical device either at the fuel filter or a regulator on the rail (?) The computer may control when the pump runs----like turning it on or off, but it doesn't care about pressure, or brand of pump (?) Nor does the computer control pressure?

As long as there is 58lbs +/- 2 lbs., the whole system is happy?
 

Babaganoosh

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i guess what i'm trying to get at here is, the computer does not know or care what the fuel pressure is? : Because it doesn't monitor fuel pressure(?) That is taken care of by a mechanical device either at the fuel filter or a regulator on the rail (?) The computer may control when the pump runs----like turning it on or off, but it doesn't care about pressure, or brand of pump (?) Nor does the computer control pressure?

As long as there is 58lbs +/- 2 lbs., the whole system is happy?
That is correct, but obviously it won't run right if the pressure is down.
 

ZooMad75

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i guess what i'm trying to get at here is, the computer does not know or care what the fuel pressure is? : Because it doesn't monitor fuel pressure(?) That is taken care of by a mechanical device either at the fuel filter or a regulator on the rail (?) The computer may control when the pump runs----like turning it on or off, but it doesn't care about pressure, or brand of pump (?) Nor does the computer control pressure?

As long as there is 58lbs +/- 2 lbs., the whole system is happy?
Most factory LS setups don't monitor fuel pressure. However, the direct-injected (DI) or LT-based engines do monitor fuel pressure. However, there are two fuel pumps on those setups. One in the tank to get fuel up to the mechanical pump driven by the cam. So the ECM monitors fuel pressure at the engine. Think of it as a diesel in that you have a lift pump in the tank and a mechanical pump driven by the engine to get to the much higher injection pressures required by DI.

Getting back to the LS or non-DI setup, the spec is typically 55-65 psi. The return-style fuel setup which is common to the '04 and earlier truck-based LS engines does have a fuel pressure regulator on the driver side rail. Technically it's not adjustable according to the book, but they usually only have a dab of paint over the adjustment screw in the center of the regulator itself. Even though the computer does not make any adjustments, the regulator does have a vacuum line connected to the intake that will allow pressure to vary based on load. As load increases and vacuum drops with increased throttle angle, the regulator increases pressure to keep the engine from going lean with more air coming in. Essentially it's blocking off the flow of fuel that was to be sent back to the tank on the return side.

The LT or DI-based engines have a specific fuel pump driver control module where it can actually vary the pressure by controlling the pump by turning it on via pulse width modulation.

There's a bit more latitude to the fuel pressure than +/- 2 psi. I've seen the truck-based LS engines run with as little as 50 psi. They don't run well and typically are setting lean fuel trim codes. They tend to really lean out under hard acceleration. South of 50 psi the engine will typically stumble and stall as the load is applied. On the other side of the scale, increasing fuel pressure is a short-term or basic way to give the engine more fuel without going through the effort of tuning the ECM. Early multiport setups like the L98 TPI engines had this done quite a bit since the early EFI was not as fast or smart as the stuff that came out later. Basically, for the same given amount of injector duty cycle if the fuel pressure is higher it squirts more fuel than it would with lesser pressure. It's not a replacement for actual tuning but a quick workaround to prove the engine wants/needs more fuel.
 

vandelay industries

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So, getting an LS engine to run on a stand, or in a car for that matter, is pretty simple. Maybe more simple than a carb/distributor setup-----because you don't have to mess with tuning either the carb or distributor?
 

ZooMad75

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So, getting an LS engine to run on a stand, or in a car for that matter, is pretty simple. Maybe more simple than a carb/distributor setup-----because you don't have to mess with tuning either the carb or distributor?
No dizzy to screw with. If you got the harness set up right it's possible to run it on the stand. If it is a cable throttle it would be fairly straightforward. If it's drive by wire you would have to have the tech module and pedal assembly set up too.

I know this with the wiring done right bit my 5.3 and 8.1 started on the first crank in the truck. Just had to prime the fuel system by cycling the key a couple of times. Lit right off.
 

bix

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One thing to keep note of is the strength of the fuel pump you use will determine your regulator style. I had opted for the cheaper option ( corvette style regulator/filter ) set at 58 psi ( shown above in this thread ) That 58 psi is only manageable by a pump realtive to the strength of the factory one. My aeromotive pump pushed 90 psi through the regulator, to the rail. I then went for the adjustable regulator with a gauge to monitor.
 

bix

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my fuel pump had a warning in the small print that it may push through some stock regulators due to the volume of fuel it moves. My gen 4 Ly5 engine had a returnless system installed from factory, but i have a return line from the regulator running back to the tank.
 
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