87 VFR 700 Fuel Pump...not pumping.

Discussion in '1st & 2nd Generation 1983-1989' started by vfrf2, Mar 29, 2010.

  1. JasonWW

    JasonWW New Member

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    I believe the safety relay provides low voltage at low rpm and higher voltage at higher rpms. It provides zero voltage at zero rpm. The 86 model has the tachometer wire go through the safety relay while later models used a wire from one of the coils to go to the safety relay.

    This is designed to shut the fuel pump off in case of a crash. If the running bike falls over the carbs will flood out the engine shutting it off, but the key will still be on. So if the safety relay loses its pulses, it will not let voltage pass.

    I think the factory pump is rated at 1 psi or there about. As the carbs fill, the floats shut off supply and fuel pressure builds up to 1 psi. The pump will stop due to pressure build up. Then as the fuel levels in the carbs start to drop, the floats open the needles and fuel line pressure is removed. The pump will click and start pumping fuel again.

    I hope this helps.

    To the original poster, did you check the contacts? That's the rebuildable part of the pump. If they are okay and working, yet it's not flowing and the inlets and outlets are not mixed up, then it's probably the diaphragm or internal pump part not working. Also make sure the plunger is moving up and down as the pump clicks.

    I remember some oem type pumps for a different model honda on ebay costing about $30-$35 dollars that was identical, but had straight fittings instead of 90° curved fittings. These pumps would work fine if you attached rubber 90° boots onto the ends.
     
    Last edited: Dec 15, 2016
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  2. squirrelman

    squirrelman Member

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    oem pump is 3 PSI.
     
  3. JasonWW

    JasonWW New Member

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    That's higher than the 1 psi I was thinking, but I'll defer to you.

    The replacement fuel pump I was thinking of was for the cbr600. They are easy to find on ebay and run about $17. They are rated for 1-2 psi.
     
  4. Ascalon

    Ascalon New Member

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    I'm intrigued by your statement.
    I've been hunting running issues with my 87 VF1000 FF that I think is a dying 2-4 pulse generator coil. This is the one that sends the signal to the fuel pump.

    However, in troubleshooting this, I have found that the fuel cut-off relay, at idle RPM, only supplies 8-9v to the fuel pump. I cannot see how this is possible, as the relay appears to be more of an electrically activated switch than a relay, so there is no reason why voltage would drop from 12+ to barely 9 in passing through it. However, if what you are saying here is correct, then the at higher RPM, more voltage flows, then that would make sense.

    I tried two different FCoRs, one from a later CBR600F2, and both do the same thing, at idle RPM, they both supply between 8 and 9V to the pump.

    How is this achieved? A mate who is better at electrickery than I am, says the wiring diagram shows a device of some sort on the line between the FCoR and the pump that he says might be responsible for the voltage drop. However, on stripping back the loom, there is a single white wire completing that circuit, and there is no apparent device in it, but the resistance of this short run (no more than 100mm) is 4 Ohms, which seems high, but seems consistent with the ‘something in there’ theory.

    I've managed to get a spare old pulse generator coil assembly and fit it, I'll be firing it up tonight (fingers crossed), but I’m just intrigued to know what the story is with the fuel pump and its apparent voltage issues.

    Cheers,

    A
     
  5. JasonWW

    JasonWW New Member

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    The VF1000 is a different engine than the vfr700/750 we are talking about in this thread, but are similar in theory. The pulse generator coils by the crankshaft don't have anything to do with the fuel relay. They provide the signal to the ecm/spark box. That's all.

    Getting back to the fuel relay, it needs a series of pulses to provide output. I don't have a wiring schematic for a vf1000, but the similar VF750 uses 2 spark boxes. Each box has a yellow wire coming out that provide 12 volt pulses. One boxes yellow wire goes to the tachometer and the other boxes yellow wire goes to the fuel relay. The fuel relay is an analog circuit, nothing digital about it at all. I don't know how it works inside the relay, but image you had an analog volt meter with a needle that swings back and forth. If you apply 12v to it, it swings over to 12v. Now if you start touching it to 12v rapidly on and off the needle doesn't have time to swing all the way over to 12 or all the way back to 0v. A decent steady pulse will make the needle kind of hover in between.

    When the engine is idling it's a slow pulse which may only let 9 volts pass. It higher rpm the pulse is much quicker so you start to see higher voltages. If the engine stalls out with the key on, the pulses stop and the relay sends out no voltage.

    I hope that makes sense.
     
  6. JasonWW

    JasonWW New Member

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    To clarify on what I was saying earlier:

    The 86 VFR700/750 gets its fuel relay signal from the yellow/green tachometer output wire from the spark box/ecm. It splits after coming out of the spark box. One to tach, one to relay.

    The 87 VFR700/750 gets its fuel relay signal from the number 3 ignition coil through a red/blue wire.

    The 88 and 89 VFR700/750 gets its fuel relay signal from the number 4 ignition coil through a red/yellow wire.

    I hope this doesn't confuse anyone, but the reason the 86 model is different in that it's fuel relay signal does NOT come from an ignition coil wire is due to the coils firing half as often as the 87 up bikes. The 87 up bikes fire their ignition coils every crank rotation (what's called wasted spark) and the 86 bikes fire only once every 2 rotations. Hence why the 86 bikes use a cam position sensor and the 87 and up do not. It's also why the 86 bikes need a special double fast output from the spark box to run the tach and fuel relay.
     
  7. Ascalon

    Ascalon New Member

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    OK, that makes sense. However, on the P/G assembly wiring, there are five wires from the connector, 2 each for the coils, and then another for signal to relay?
    I know it might go through the ignition box, but it was my understanding that it was one of the pulse coils (2,4) that originated the signal for the cut off relay, so that it was not just key on dependent.
     
  8. JasonWW

    JasonWW New Member

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    I found a schematic for the F model, not FF, but it should be the same. The 5th wire in the connector is for the oil pressure switch, so it's unrelated.

    You should have a blue wire from the 2-4 spark box going to the 2-4 ignition coil and that blue wire tees off and goes to your fuel pump relay.
     
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