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TBI conversions and angles

Discussion in 'The Garage' started by Mastiff, Jul 18, 2004.

  1. Mastiff

    Mastiff 1/2 ton status Premium Member

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    I'm working on converting my carb to a TBI, and I'm trying to get away with an in-line fuel pump instead of modifying the tank. I see that the Holley pump wants to be below the fuel level in the tank to get a good gravity feed. But then, what happens if I'm going up a steep hill? The gas will be way below the fuel pump, is the pump going to fail and choke off my system just like a carb (or worse)?

    What does it take to convert my whole gas tank to an EFI style with in-tank pump?
     
  2. Hossbaby50

    Hossbaby50 3/4 ton status

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    If you are not going to swap in a baffled tank then just make sure you don't get below 1/4 tank while wheeling. Otherwise you might uncover the pickup at angle and choke the motor.

    Sofar I have not had a problem with my external pump and my TPI setup. I make sure to top off before I head for the trails though.

    Harley
     
  3. ntaj*ep

    ntaj*ep 1/2 ton status

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    TBI only needs about 10 PSI, you shouldn't need a powerful pump. Holly and most others for that matter, want the pump below the tank in case you starve the pump it will re prime eaiser.
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    It's pretty easy to swap the tanks. The tanks are externally the same, but the inside has a baffle, and the TBI sender is somewhat difficult to find. You can get the senders new for about $180. (gastanks.com)

    Looks like you could be into a new tank and sender for about $300.
     
  5. Mastiff

    Mastiff 1/2 ton status Premium Member

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    [ QUOTE ]
    It's pretty easy to swap the tanks. The tanks are externally the same, but the inside has a baffle, and the TBI sender is somewhat difficult to find. You can get the senders new for about $180. (gastanks.com)

    Looks like you could be into a new tank and sender for about $300.

    [/ QUOTE ]

    That would be an 87-91 tank? What exactly is included in the sending unit? It's the top cover thing, plus the lines going down into the tank? To do the total swap, I'd need a new tank, a sending unit, and a fuel pump, is that correct?

    Thanks. /forums/images/graemlins/thumb.gif
     
  6. TrcksR4ME

    TrcksR4ME 1/2 ton status

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    Since I am a moron when it comes to these things...

    If a TBI only needs about 10 psi why can't you get a high output mechanical fuel pump if you are doing a swap?
     
  7. ntaj*ep

    ntaj*ep 1/2 ton status

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    Needs a constant 10 psi mechanical pumps are too inconsistant, also it needs pressure at startup which a mechanical pump in incapable of.
     
  8. TrcksR4ME

    TrcksR4ME 1/2 ton status

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    Ahhh, that makes sense. I hate the idea of fuel pumps in the gas tank, to me it sounds like one of those things auto makers came up with to increase the cost of repairs on their vehicles /forums/images/graemlins/deal.gif /forums/images/graemlins/dunno.gif /forums/images/graemlins/screwy.gif
     
  9. Hossbaby50

    Hossbaby50 3/4 ton status

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    In tank pumps are actually more reliable then external electric pumps. The easy way to get around having to drop the tank to get to the pump is cut an access hole in your floor. Then make a plate to cover the hole that is removable.

    Harley
     
  10. y5mgisi

    y5mgisi 1 ton status

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    like this!
    [​IMG]
     
  11. justinf

    justinf 1/2 ton status

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    I run an inline fuel pump from an 89 Furd F150 with a 302 that I use in the jeep, got it at Autozone with a lifetime warranty. It is mounted just above the bottom of the tank, and I have had no problems unless I get below a quarter tank of fuel, then like was said earlier, it uncovers the pickup. Other than that it works great, and If I remember right it was about $75 I think.
     
  12. Hossbaby50

    Hossbaby50 3/4 ton status

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    How many PSI does that pump put out?

    Harley
     
  13. Mastiff

    Mastiff 1/2 ton status Premium Member

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    [ QUOTE ]
    I run an inline fuel pump from an 89 Furd F150 with a 302 that I use in the jeep, got it at Autozone with a lifetime warranty. It is mounted just above the bottom of the tank, and I have had no problems unless I get below a quarter tank of fuel, then like was said earlier, it uncovers the pickup. Other than that it works great, and If I remember right it was about $75 I think.

    [/ QUOTE ]

    Why is the uncovered pickup only a problem with electric pumps? If the mechanical pump was sucking air, wouldn't that also kill the motor? I don't see why this problem suddenly appears when you switch to EFI.
     
  14. Hossbaby50

    Hossbaby50 3/4 ton status

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    EFI pumps usually pump alot more fuel then the mechs do I believe. Therefore it would starve the motor faster. A mech pump can probably be starved to but it won't happen as fast as with FI.

    That is why you must have a fuel return line with FI and not mech. You have to have a way to get the unused gas back to the tank to be recycled with the FI.

    Also if you were at enough angle to starve the mech pump you are probably at enough angle to have the carb the mech pump is feeding run poorly too.

    Harley
     
  15. dyeager535

    dyeager535 1 ton status Premium Member

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    [ QUOTE ]
    If the mechanical pump was sucking air, wouldn't that also kill the motor?

    [/ QUOTE ]

    Carbs have float bowls full of fuel to draw from even if the pump is starved for a bit, and they aren't run under pressure once the fuel enters the bowl. This is why some Q-jets have hard start problems when they sit...the fuel leaks out of the bowl, and the pump needs to move fuel up into the float bowl before the carb starts dumping fuel again.

    If EFI loses pressure, it dies...the injectors can't spray if there is nothing pushing fuel through them.
     
  16. justinf

    justinf 1/2 ton status

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    [ QUOTE ]
    How many PSI does that pump put out?

    Harley

    [/ QUOTE ]

    I believe it's somewhere around 15 psi. It works great for the TBI 350 in my jeep.
     
  17. Mastiff

    Mastiff 1/2 ton status Premium Member

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    [ QUOTE ]
    In tank pumps are actually more reliable then external electric pumps. The easy way to get around having to drop the tank to get to the pump is cut an access hole in your floor. Then make a plate to cover the hole that is removable.


    [/ QUOTE ]

    Okay, so with the external pump, there is the problem of the pickup sucking air. Why is it not a problem with an in-tank pump? I mean, the pickup for the external pump could be at the exact same spot as the intake for the in-tank pump, so why would it be different? Why is an in-tank pump not a problem but an external pump is?
     
  18. dyeager535

    dyeager535 1 ton status Premium Member

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    With the same sending unit, there wouldn't be a problem per se, but there would be the fact that as the fuel drains out of the system, (like overnight for instance, not while running of course) the in-tank pump is still submerged in fuel, where the external is now having to move air to get fuel to it.

    A little different than the question posed, but perhaps the external pump questions are raised in anticipation of not using a TBI sender..

    I have to look at my TBI sender, but the TBI sender fuel return line might well extend all the way to the base of the tank...that way all returned fuel would be returned to the "sump", which would obviously make fuel starvation even more difficult. I should take a look at that, have to change my sender anyways. /forums/images/graemlins/frown.gif
     
  19. justinf

    justinf 1/2 ton status

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    [ QUOTE ]
    [ QUOTE ]
    In tank pumps are actually more reliable then external electric pumps. The easy way to get around having to drop the tank to get to the pump is cut an access hole in your floor. Then make a plate to cover the hole that is removable.


    [/ QUOTE ]

    Okay, so with the external pump, there is the problem of the pickup sucking air. Why is it not a problem with an in-tank pump? I mean, the pickup for the external pump could be at the exact same spot as the intake for the in-tank pump, so why would it be different? Why is an in-tank pump not a problem but an external pump is?

    [/ QUOTE ]

    If you did not use a TBI tank with internal baffles, then I think you would still have problems with the pickup sucking air when the fuel level in the tank dropped far enough. TBI tanks combat this problem with baffles so the fuel is not sloshing all over.

    I run an external pump with the stock jeep sender and pickup in the the stock jeep tank. The only time I have problems is when the fuel level drops below a quarter tank, and the fuel is sloshing around (on inclines, or sometimes hard turning/driving). Easy driving on flat ground isn't a problem. BTW, I can wheel for two days easily on one tank of gas, this is even with the engine running a little rich and idling high (I am working on straightening out these issues now).
     

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