Carb to Fuel injection conversion

Discussion in 'Gas Engines' started by bravloue, May 14, 2008.

  1. bravloue
    Joined: May 2008
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    Location: Florida

    bravloue New Member

    A couple of years ago I upgraded my boat with a new fuel injected Volvo Penta 320 HP Ocean Series Drive. The old drive was an OMC carbureted drive. When the tank gets down to about 3/8 the motor starts to bog down and the fuel pump whines. The motor will idle OK and will get the boat back on plane but after 20 or 30 seconds the motor starts to bog down again. (I know this is becuase I never installed a lift pump to the fuel pump but I do have a couple of additional questions).

    The old carburetor (like all carburetors) is vented. If the tank gets low and the pump starts to suck air (from fuel splashing in the tank) the air will be vented out in the carb bowl (this is my theory, for what it's worth, probably not much).

    Could my problem be from sucking air or is it strickly a lack of suction from the main fuel pump? Do I need a high pressure pump or low pressure? Can anyone recommend a good lift pump?

    Thanks.

    Lou
     
  2. kenJ
    Joined: Jul 2005
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    kenJ Senior Member

    Is the pickup tube long enough or perhaps too long so it's floating off the bottom of the tank? If the pickup tube is rubber, perhaps it is cracked allowing it to suck air when the fuel gets low. If the engine runs fine with a full tank, I wouldn't think an extra pump is needed, I'd inspect the pickup inside the tank.
     
  3. bravloue
    Joined: May 2008
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    bravloue New Member

    Pickup tube

    This is a poly tank with a aluminum fitting on the pickup tube. The pickup tube is seized to the fitting, I am afraid if i put too much torque on it somthing will give other than where it's supposed to. I was trying to avoid extra work if a fellow mechanic told me the pump would fix it but it sounds like I am going to have to put the torque to that fitting.

    Thanks for your advice.

    Lou
     
  4. CDK
    Joined: Aug 2007
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    CDK retired engineer

    For an injection engine you need two fuel lines and a fuel collector near the injection unit. The return line transports excess fuel and air bubbles back to the tank.
    By far the best solution is a submerged fuel pump like in all modern passenger cars. It is much easier to pump fuel out than to suck it out. These pumps are mounted in a plastic housing with filters. The construction is such that the fuel level in the housing is higher than in the tank itself. Splashing has no effect on the fuel flow and these pumps are able to operate reliably until the last drop. Chose a pump from a car engine with similar HP or somewhat less, they are designed to supply 150% of the required amount while maintaining their rated pressure.
     
  5. bravloue
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    bravloue New Member

    Sounds like the system with two fuel lines is what I need. Did the "collector" come with my new enegine? I will be on the boat this weekend and see if there is a device similar to what you are referring to. From my recollection all there is, is an NPT fitting right on the fuel pump which came mounted to the engine from the Volvo Penta Factory. Also, are automotive fuel pumps (lift pump) Coast Rated for marine environment in an engine compartment?
     
  6. CDK
    Joined: Aug 2007
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    CDK retired engineer

    The fuel collector is little more than a cavity at the beginning of the fuel rail or injection pump body (there are mechanical and electronical systems). It has one NPT fitting where the fuel line is connected and another one mounted on or near the top for the return. In a single fuel line system the upper one is plugged.
    The fuel lift pump I have in mind isn't mounted in the engine bay but in the tank at the bottom. That may feel a bit weird an dangerous, but firstly these pump are of the brushless type, so there are no sparks, and secondly they operate in an environment where there is only liquid fuel and fuel vapour, so no danger of explosion.
    You could also opt for the old-fashioned external pump that looks like a beer can. The pump itself is not dangerous, but the connection to the fuel line is, because you'll need a piece of fuel hose and clamps at both sides. That's why these pumps in passenger cars were always mounted under the cabin bottom where airflow is quite high.
    Thinking about it: I once owned a Maserati Ghibli with two of these pumps mounted in the boot, but that was 30 years ago when safety standards were nonexistant. I doubt if such a pump exists with a Coast Guard certificate.
    The submerged pump requires no certificates: its environment in a boat is identical to that in a car.
     
  7. bravloue
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    bravloue New Member

    Thanks so much for the info. I will check it out this weekend and let you know what I found on Monday.
     
  8. broke_not
    Joined: Jun 2008
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    broke_not Junior Member

    I've had quite a few of the in-tank pumps apart, and haven't come across a brushless style motor in one yet.

    It's tough to find a good picture of one taken apart, but here's a link to a page with some automotive in-tank pump repair/replacement info:

    http://www.rangerovers.net/repairdetails/fuelpump.htm#rebuild

    One of the photos from that page:

    [​IMG]

    ;)
     
  9. CDK
    Joined: Aug 2007
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    CDK retired engineer

    The pump in your photo definitely has brushes. I've not seen as many pumps as you did but it seems to make sense to me that in a gas tank you should not use anything that can spark. I replaced the pump in my Isuzu/Vauxhall/Opel with a Bosch pump meant for BMW: both were of the brushless type with hall sensors.
    The fact remains that the air/gasoline mixture in a tank is saturated, so it cannot explode. Landrover does make mistakes I suppose, but not of this magnitude.
     
  10. broke_not
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    broke_not Junior Member

  11. CDK
    Joined: Aug 2007
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    CDK retired engineer

    A simple way to build a brushless DC motor is using hall sensors to detect the change in magnetic fields and mos-fets to do the actual switching. A 4-pole motor has 4 such devices on a small circuit board, a rotating magnetic ring and static field windings. In small motors they use hall sensors and bipolar transistors in one plastic package. Texas Instruments was the first supplier with their TL-17x series. No sparks, no wear, no RF-interference.
     

  12. broke_not
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    broke_not Junior Member

    Okay, I can see using Hall Effect sensors in the construction of a brushless DC motor, but is anyone currently doing it with fuel pumps? I haven't seen one myself, but a quick Googling led me to this:

    http://findarticles.com/p/articles/mi_qa3828/is_200609/ai_n17191951/pg_1

    This part in particular caught my eye:

    It sounds as if the idea will work, but practical application of the idea hit a wall due to cost and complexity. I searched for a few minutes trying to find a source for purchasing a brushless pump that operates in the manner described and came up empty. Many links to Chinese companies, and many more to "free patents" websites.

    Do you have a link to the model you have?
     
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