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Old 02-26-2020, 09:47 AM   #36

hatzie's Avatar
Join Date: Oct 2008
Location: Wentworth, NH
Posts: 3,944
Re: SMOG LEGAL ENGINE SWAP TO LS yesterday passed!

You can use the 87-91 saddle tanks with the baffles and senders with fuel pumps as high volume low pressure lift pumps and a fuel pump on the frame rail to push the pressure up to LS specs. You'll need to upgrade the NL2 dual tank valve to the motorized Pollack valve. The NL2 wiring and switch will need to be updated to the 1987-91 TBI setup using the fuel system power wire from the LS ECM in place of the same from the TBI ECM. This allows you to keep your 40 gallon capacity with two tanks.
The LS ECM should cut fuel pump power as soon as the engine stops so... as long as you're switching the fuel pump power with the ECM you don't need the oil pressure switch as a safety system.

The 1987-91 Emissions and Driveability books in my manuals thread have detailed information on how the power feed from the ECM feeds the fuel pump relay and the NL2 valve power. Look up the Dual tanks theory of operation thread for more information as well.

Several European and US automobiles use the in-tank HVLP lift pump to HP fuel pump scheme for fuel supply.

The TBI pumps will push significantly more volume GPH or GPM at lower restriction/pressure.

When tanks without baffles are your only option you can put a submersible LS fuel pressure pump in a slosh can with feed and return to-from the tanks and to-from the fuel rails. It's not needed with the 87-91 TBI fuel tanks.
1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8

RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.
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