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Old 02-29-2020, 03:33 PM   #37
68c10owner
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Location: Carmichael, California
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Re: SMOG LEGAL ENGINE SWAP TO LS yesterday passed!

Quote:
Originally Posted by hatzie View Post
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.
Thanks,great Info here. If I stick with the saddle tanks I will change them to the 1987 TBI tanks but I am also considering a blazer tank conversion. My main issue is making everything smog legal. I know they need a vapor pressure sensor or something like that. Figured swapping to a single tank would make things easier. The swb saddles are only 16 gallons each so I wouldn't be losing too much and rarely filled both tanks in previous trucks.
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