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Discussion Starter · #21 ·
I just thought about something , if I was to plug the relay back in , start the bike up and let run. If I unhooked the pump if the relay is good I should get voltage going to the pump right? I'm no expert at this but I would think it would if the relay is good.am I right it wrong?
 

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1983 Honda vt750 Shadow
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You could try that with a 12 volt light bulb as a test. If it lights that means it CAN work. Then connect the pump and see if the pump works. It may be that an old pump starts drawing too much current and the electronic relay can't pass that much.
That is just a guess out of the blue.
And if you connect the pump directly to battery power with the green as ground, it should pump steady.
 

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Thanks Swifty, for the info on the fuel pump relay. The one in my '96 1100 ACE is driving me crazy. Doesn't seem to work, although the fuel pump clicks away merrily if I jump Black to Black/Blue. The replacement I purchased was a take-out and behaves just the same.

I tried supplying both B+ and B- to the trigger terminal (Blue/Yellow) of the relay, but it doesn't close with either of those. I guess it's not so simple as that, it wants to see ignition grounding pulses in order to close? What I didn't realize until now, was that the engine needs to be spinning for the relay to provide power to the fuel pump. I guess this is why some folks install a priming switch to temporarily jump the fuel pump on and fill the bowls, before they start cranking.

When jumpered on, my fuel pump slows down, but doesn't cut off. Does this mean I have a leak in the fuel lines or a leaking float valve? Somewhere I read that the fuel pump has the ability to sense back pressure and an internal cutoff?

By the way, I was incorrect about the Kill switch, it has no effect on the fuel pump supply circuit. If the relay is bypassed, the fuel pump will continue to run as long as the ignition is on, which is a safety issue.
 

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If it is a factory style pump, it will shut off about 2-3 pounds.
Squeeze off the pump outlet hose to verify that is how it works, and then you know if there is a fuel seepage somewhere too.
Some aftermarket pumps continue to click, but bypass internally at the pressure level.
 

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You could try that with a 12 volt light bulb as a test. If it lights that means it CAN work. Then connect the pump and see if the pump works. It may be that an old pump starts drawing too much current and the electronic relay can't pass that much.
That is just a guess out of the blue.
And if you connect the pump directly to battery power with the green as ground, it should pump steady.
That would be a hope, but when my ‘bad’ pump was forced to keep operating, it blew the relay up.
 

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With the info from Swifty, I checked the fuel pump relay on my '96 1100 ACE today. Running the bike gravity fed from a hang tank, with the relay connected as it should be, pump delivered about 1liter/min. I continued to run the engine from the hang tank and looped the clear hose I had attached to the fuel pump outlet over the top of the bike and into the inlet hose to the fuel pump. I could see the fuel moving through the hose, as I did the rest of my tests.

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I back-probed the relay connector and hooked the trigger signal for the fuel pump relay from the front cylinder ignition primary circuit (Blue/Yellow) to channel 1, and the relay output to the fuel pump ( Black/Blue ) to channel 2 of my Hantek 1008C USB oscilloscope. My Kelvin DMM was also measuring the relay output. I'm running the bike off a car battery next to the bike, and the carb throats are wide open for this test.
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The ignition signal yellow has quite an inductive voltage spike happening, so I used a 20:1 attenuator on channel 1. With 500mV per division vertical for channel 1, I was seeing about 40V peak/peak on the primary spike. Channel 2, the relay output looks like a constant 12V, but this is only over the horizontal time base of 200 microseconds per division that gave the best view of the ignition spike. That's only 1/500th of a second on the screen. The DMM was displaying 5.6 to 6.0 VDC, on the DC scale, so the power pulse must be cut off for a substantial percentage of the time between ignition pulses.

If my math is correct, at 1000 rpm, there will be 60 / (1000 / 2) = .12 seconds between ignition pulses, so I need to look at a time base more like 10 msec / division if I want to see the shape of the fuel pump power pulses.

A friend showed up on his Genuine Buddy 150 scooter, (like riding a dining room chair) so we went for a ride, and I didn't get to that test, or the fuel pump pressure test, but I'm happy that, with the forum's help, ( esp. Swifty ) I finally understand how this fuel cutoff relay and fuel pump works. Also, I finally have the jetting to my satisfaction at 180/45 front and 185/45 rear, so I think it's time to button it up and put the tank on.

I want to replace the flimsy wire fuel line clamps, and still need to recover the seat, but getting close to riding this one.
 

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Good to hear your results, although a bit above my head.
I love electronics, but don't understand all the deeper info.
I only have an analog scope so a bit outdated !
 

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Discussion Starter · #29 ·
Yeah I read that twice and still have no idea what most of that means , lol but thank you for taking the time out of your dad to figure all that out. That was really cool of you ,
 

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Yeah I read that twice and still have no idea what most of that means , lol but thank you for taking the time out of your dad to figure all that out. That was really cool of you ,
Well, I thought I had a pump relay issue, so I was mainly resolving that, but documenting it in your thread. One thing that my experiment means is that I've confirmed that an operating relay, when measured with a digital volt meter, shows quite a bit less than 12V. You said in your other thread that you had measured around 4-5 volts. I measured 5.6 - 6.0 with an operating fuel pump.

I think that the current through the thyristor output device IS affected by the downstream circuit, so I wouldn't be at all surprised if the voltage displayed was different when it's feeding an open circuit, ( like your measurement), vs some impedance, like my measurement. I would bet that number changes with rpm too. It would also be reasonable to expect that more current would flow and could destroy the relay circuit, if somebody's fuel pump failed with a shorted coil, ( like Troy's situation may have been).

Anyway, ... it's not unreasonable to expect that your relay is still good. You'll find out when your pump arrives.

Folks might also like my trick of looping the pump output, through a clear tube, back to the pump input. Once the fuel pump and filter are primed with a little gas, you can see the pulses surging through the clear tubing round and round, as the engine runs off the gravity tank. My 1100 ACE is too fricking loud to hear the pump with the engine running. Maybe I'll put a clear plastic filter inline, just for fun, to act as a sight glass.
 

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Discussion Starter · #31 ·
Ok I kinda get what your saying , I thought you had 9-10 going to the pump with the relay plugged in or unplugged. I tested mine with it plugged in. I probed the back of the connecter feeding the pump.

If my dad was still around he would have been able to be figure it out for sure , he was real good at troubleshooting electrical stuff. Most of the time he wouldn't even need to look at a book or diagrams. I really miss my dad sometimes
 

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Discussion Starter · #32 ·
Installed the new pump and relay a lil bit ago and I have fuel pumping again , filled the bowls before I connected the outlet hose to the main line so I could start it up and make sure it was working. I took it around the neighborhood for a few and seems good. I plan on taking it back out so I can get on it a lil bit see how it acts, I'm sure it's good to go but for now I'm staying off the highway until I know for sure. Lol I didn't even try using the old relay though. I think I might take the old one apart and take a look at it. Would like to know what went wrong with it. Just wanted to say thank you to everyone that gave me some advice.
 

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Thanks for closing the circle, glad you got your Shadow rolling.

If you do surgery on the fuel pump, please post a few pictures and a description of what you found here.
 
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