My blade ruins fuel pumps.

Discussion in 'Maintenance' started by Paddyk, Jul 31, 2020.

  1. Black & White

    Black & White New Member

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    We're getting off piste here. Smiley face emoji.
    I'd get an assured-quality replacement pump, connect it electrically but leave fuel lines off. Switch ignition on and check it primes for two seconds, then see if the pump runs when cranking. For some insurance, maybe swap the 30A fuel pump fuse for a 15 or a 20. The 20 shouldn't pop under cranking. If all's well, fit the pump in the tank & do the fuel flow test (Chapter 6-45 of the 2008-on manual). If that's all good, the only thing left that could be at fault is a blockage after the pump. Any restriction which causes the pump to work harder than normal will definitely increase its current demand.
     
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  2. RR7

    RR7 New Member

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    I'm not sure what is causing the problem but assuming any pump will draw greater amps when dead headed against a blockage, or starved on the suction, is wrong.
    Any obstructed pump will draw a minimal amperage required to just spin in a fluid. A pump draws amps in relation to the mass flow moved. Restricting a petrol pump would cause the amps to fall, and eventually to vapour lock the pump if sufficient cooling was not available. The trick to understanding is that pumps reflux against a closed outlet, ie. they internally recirculate.
     
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  3. Black & White

    Black & White New Member

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    This gives a trouble shooting conclusion @ around 5.30, which I think is not wrong.
    Centrifugal, impeller type pumps will internally recirculate, but roller cells (as this type of pump is) won't internally recirculate because they seal too well, depending on liquid viscosity. If you watch the amps rise when he first bypasses the relay, it goes from the 'surge' (motors max out on start-up) current of 3 amps up to 5.6A running current as the pressure increased. These are positive displacement pumps so that cavitation and vapour locks are avoided, particularly important on Diesel engines. Their high pressure pumps are putting out 2,000 bar and can only be engine driven. An electric motor would require too much current on a 12V or even a 24V system.
     
  4. RR7

    RR7 New Member

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    This is the typical head/flow/power characteristic of an in-tank fuel pump.
    https://www.aemelectronics.com/site...rent-vs-pressure-50-1000-1200-1215-1220_0.jpg

    These are the Affinity Laws that cover both centrifugal and positive displacement pumps.
    https://www.sugarprocesstech.com/pump-affinity-laws/

    If you can find a manufacturer's characteristic for a pump able to behave as you describe I'd be interested.
     
  5. Black & White

    Black & White New Member

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    That was interesting, thanks for that @RR7.
    The affinity laws regarding impeller pumps seem straightforward, insofar as speed/size matters(!), but the equations regarding positive displacements largely ignore those factors.
    The chart on the first link shows current flow increasing almost directly proportional to restriction..... Which was my point, so thanks for that.
    It's exactly the opposite from what you were saying. So thanks again. You said current demand drops as pressure increases.
    It would obviously peak at some point where line pressure overcame the pump's internal sealing pressure, or the pump stalled, and then we'd get a lockdraw/current reading.
    Anyway, now that's established, what I'd find way more interesting is a solution to the OP's problem, in that his bike keeps 'burning out' fuel pumps.
    You were saying that it was not possible for a pump to exceed its (or its fuse's) rated current capacity due to a restriction, so you have ruled that out then, in the face of the graph you linked that indicate the contra.
    What's your suggestion as to why the pumps keep on failing, or are you trying to emulate a famous Monty-Python sketch in that you came for an argument......? fuel-pumps-flow-current-vs-pressure graph.jpg
    The Fireblade fuel system is meant to run at 3.5 bar, which is around 50 psi. Your graph shows we've got around 12.5 amps at that pressure, which wouldn't blow a 15 amp fuse (or a pump able to handle 15 amps max).
    If a restriction was introduced that brought the pressure up to, I don't know, 95 psi? What's the amp reading, and how would our 15 amp fuse (or pump) fare then?
    It appears to me that current flow increases with motor/pump load, or am I reading it wrong?
     
  6. Paddyk

    Paddyk New Member

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    As a new member I am amazed and thankful for all the help that you are giving me.
    The bike is a rry 2000 with 17000 miles
    The replacement pumps are genuine Honda
    I am wondering if the rectifier could be giving too high a voltage when the engine is running ?
     
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  7. Marc

    Marc Member

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    I'm not an expert, far from it. The only thing I can add is that my RR6 has been suffering with a faulty reg/rec recently and that was frying the battery rather than anything else on the bike.
     
  8. Black & White

    Black & White New Member

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    Are you saying your bike runs for a while before the fuel pumps fail?
     
  9. dern

    dern Active Member

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    This might be a red herring but if you're got a spare hour to eliminate this... Hondas of that age have a common problem with corrosion of the common earth block. You'll find it on cbr600s, blackbirds, all sorts. Find the common earth block and replace it with something less manky if you find any corrosion in it. On my blackbird I soldered ring terminals on all the grounds going in to the block and bolted them all to the frame. The earth block going bad throws up all sorts of weird issues and is worth eliminating.

    I had a fuel pump go on my 929 but in my case replacing it with a second hand unit fixed the issue which is no help. One stupid thing about the wiring loom on those bikes is that the low fuel sensor shares the same connector as something else in the loom (can't recall what) which blows the low fuel sensor if you connect them the wrong way round... you've not had the thing apart to that degree have you?

    Anyway, check the earth block and see if it's corroded.

    ETA: Load of info here... https://www.fireblades.org/threads/electrical-gremlins-finally-caught-them.75556/
     
    #29 dern, Aug 20, 2020
    Last edited: Aug 20, 2020
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  10. Paddyk

    Paddyk New Member

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    The bike is a 2000 model with only 18000 miles
     
  11. Paddyk

    Paddyk New Member

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    Hi it's a 2000 model
     

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