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Ls1 on lt1 fuel system

Old 03-23-2019, 12:43 PM
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Ls1 on lt1 fuel system

1994 z28 with rebuilt 5.3swap and 4l60e .1st time done by me and I'm sure there are some simple thing I've done wrong or missed . Im having issue getting all my vacuum and evap purge hoses connected correctly. Are there photos or diagrams to shows exacts on vacuum, evap connections as well going in a 94 . I was having pressure build up in fuel tank. So I asked on another forum and was noted that I should change fuel pump to at least 255 lph so I did. Now I've changed and still having them. I'm almost certain my evap is connected. Can anyone help?
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Old 03-25-2019, 10:46 AM
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Re: Ls1 on lt1 fuel system

The LT1 and LS1 fuel systems are radically different.

- Totally different fuel tank/vent/canister/fill pipe configuration

- Different operating pressures (LT1 3 bar/43.5 PSI, LS1 4 bar 58 PSI)

- Recirculated system in the LT1 with vacuum compensated pressure regulation on the return side at the rails, dead-ended (except early Corvette LS1 - recirculated) LS1 system with non-vacuum compensated pressure regulator at the tank.

All those differences need to be accounted for, if you are trying to interface the LT1 fuel system components with the LSx PCM.
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Old 03-25-2019, 01:06 PM
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Re: Ls1 on lt1 fuel system

Thanks for information. Yes 5.3 pcm. Are there steps to making this work for me. That I can follow or any links.
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Old 03-25-2019, 04:41 PM
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Re: Ls1 on lt1 fuel system

You will have to get input from someone who has actually done the engine swap. I am not aware of anyone here, and seems like the only people left here are LT1 owners. Maybe someone will chime in. I helped someone on this site swap an LS1 model fuel tank into an LT1 chassis, and it was a major nightmare, because of the venting issues. He couldn't even pump fuel into the tank because it seemed like there was no way for air to get out of the LS1 tank to let the fuel in any faster than a dribble. He sorted it out eventually..

One thing that would seem to ease the problem is using the LS1 fuel rails from a 97 Corvette, that use a recirculated system. That way you would just need to connect your existing supply and return lines to the LS1 rails, incorporating an adjustable fuel pressure regulator in the return line. Bump the pressure to 58 PSI, don't use a vacuum compensation line.

Why did someone recommend the 255 LPH pump? It would make sense if they recommended the "high pressure" version of the Walbro, since the stock LT1 pump isn't going to flow as much at 58 PSI, vs. the LT1 running at 43.5 PSI. I've got dual high pressure pumps rated at 205 LPH, and run my LT1 fuel system at 58 PSI, and a single pump will support the 500 HP it makes normally aspirated. I only need to run the second 205 LPH pump when I need extra fuel for the 300-shot of nitrous (dry system, all the fuel goes thrugh the 74 #/HR injectors).

The EVAP system is going to be a big issue. Do you even need the EVAP system, for example to meet emissions? The PCM is programmed to activate the EVAP system based on things like mass air flow, fuel trims, engine coolant temp, and intake air temp. The PCM diagnostics for EVAP system performance rely on things like the fuel level in the tank (not connected to the PCM in 94) , the throttle position, and the pressure in the tank (no pressure sensor in a 94). You can run without the EVAP system, eliminating issues with the canister and the vacuum connection. You would use a vented fill cap, and may notice a bit of fuel smell at the rear of the car.

Last edited by Injuneer; 03-27-2019 at 11:05 AM.
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