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When I converted my '89 F250 to remove the EFI 5.0 and use my carbed 351W, I replaced the leaking front tank with a new tank and stock '89 sending unit minus the pump. I used a copper tube to extend the pickup to where the original pickup point was in the tank. I removed the existing fuel and return lines and ran a single new line to the mechanical pump. Rear tank was defective and was deleted.
My understanding of my original '89 fuel system is that the switch controlled the in-tank low pressure pumps and senders only and did nothing to the high pressure pump on the frame rail. Since I no longer have an in-tank pump my switch controls only the sending unit. Switching to "rear" does nothing. The dual function reservoir is mechanical only.
Don't know if this helps any.
Gary,
Yes I do plan on using a carb but the discussion at hand is how to use my existing tank selector switch for the tanks. My thoughts or hopes were to be able to use in tank fuel pumps, get rid of the high pressure pump, inertia switch, and computer and go from the cut off relay to power the selector switch which in turn would power either front or rear tank.. depending on the pressure the in tank pump should have enough pressure for the carb to run efficiently.
The computer only grounds the relay. Here it is in the EVTM, with what appears to be both power and ground coming from the computer, meaning ZZ and YY respectively:
But here at ZZ we see that the power actually comes from the same source that supplies the computer, which is Fuse Link Z:
And here at YY is where the computer provides the ground:
I've mentioned a number of times the 'Hot Fuel Handling' system.
You could use a simple oil pressure switch to "make" ground on the pull down of the fuel pump relay.
The only issue is priming, when all the fuel in the carb may have evaporated if the truck sits for a month.
This is where the "needlessly complex" bypass circuit comes into play.
You'd need to attach a 20Ga. fuse link and a diode from the 'I' terminal of the fender mounted starter relay to a point after the fuel pump relay.
I do want it as simple as possible I promise. I'm just a little hesitant of pulling the timing cover to see if it has what I need or to add what is needed to run the mechanical pump. If I abandon everything that is existing would it be too difficult to just run a low pressure electric pump? If it's low pressure I shouldn't need the return lines I am hoping. As far as the 2 tanks go I may just run off 1 to get this thing going.
I have found anot her fuel rail with injectors and a harness for 80.00 but I will still have the same problem with the fuel system and then as previously stated I have no idea if the computer works or any of the sensors. Even though efi is more efficient I still think in this case It'll be easier going to carb
Just look behind the power steering pump and see if you have a block off plate on the side of the timing case...
If you do, remove IT, and use a mirror to confirm the eccentric.
No one is suggesting you pull the whole front off the engine to 'check'...
Then you could get a $35 mechanical pump that has the return built in.
I have no idea if there's any difference between 302 & 351 applications
Electric pumps do a MUCH better job of *pushing* fuel than they do of pulling it... the in-tank pumps exist to get the flow going from the bottom of the tank to up and over the top and thereby supply a feed for the high-pressure pump. Think of trying to start a siphon, it's the same thing.
In any event, if you use such a setup, I would recommend a return line regardless just to keep the pump from dead-ending (pushing against a brick wall) and getting hot and burning out as a result.
I don't remember enough of this thread to remember what the exact issues here are...
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