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The reason that I say to go with a carb/DSII set up is that he can remove the computer completely and not have to worry about it. Yes, swapping to Carb/DSII would be more involved, and would produce poorer gas mileage than EFI, but in my opinion it would be easier to maintain in the long run. No sensors to worry about, no computer, less wires, etc.
But you're right, it would probably be a more plug and play procedure, and another thing I didn't think about is emissions. It'd be pretty difficult to pass emissions with the Carb/DSII, assuming that he still has to pass emissions where he lives.
Emissions is the other issue like you stated. It would never pass where I am if I down graded from FI to carb. That and he will have to get a fuel pump regulator to lower the pressure since carbed motors dont have the fuel pump in the tank like his truck does.
Thankfully, in GA, you don't have to take an emissions test if your vehicle is 25 years old or older.. For now, anyway.
And I didn't even think about the fuel pumps. Like you said, swapping to a carb would require a pressure regulator, or removal of the in-line and in-tank fuel pumps, OR a new tank, plus he'd have to install a mechanical fuel pump, and the EFI engine might not even have a slot for a mechanical fuel pump. Good point.
You can remove the cover that is over the fuel pump inlet on a non carb motor. However I would prefer the FI just for the easy of starting and such in the cold.
I think I'm definately going to go the carb'ed route. Just simpler to maintain, and probably the same or less work than changing over to mass air from speed density.
Will I be able to run a mechanical fuel pump and just disconnect my electric ones?
The 351W out of the 87-92 was NOT mass air it was speed density. They did not go to mass air until after 92. Therefore the upper lower intake and computer that I have would work just fine for your truck without any conversions.
The speed density system sucks It sucked since I got this truck in 1987. It's got horrible throttle response. If nothing else I'd pull that off and stick a 4 barrel on it this spring when i pull the cats. But it could use some gaskets and should probably be pulled out to do it righ so nows the time to do a fresh 351. But the fuel injection ain't staying.