85 700 fuel pump and relay questions - Honda Shadow Forums : Shadow Motorcycle Forum
 
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post #1 of 10 (permalink) Old 09-28-2009, 07:36 AM Thread Starter
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85 700 fuel pump and relay questions

1985 VT700, been hard to start lately, cleaned carbs a souple of times, with mixed success, but fuel pump started acting up. Normally hear the ticking when ignition turned on, varies if petcock opens, but does not seem to shut off in a couple of secs like I hear that it should, so I figured PO bypassed the relay and it did not need the signal from the igniter box. Anyway, went to start it, and no ticking, no start, gas level pretty low. Sometimes get a few ticks, but really sluggish sounding pump. Checked voltage at the pump connector just to be sure, and it's got voltage. Tried to probe connector when disassembled and meter probe slipped out of place and shorted two pins together, made spark, now dead, figured a fuse popped. I looked, no fuse seems to apply to this circuit, all seem OK. What's funny, is that "relay" seems to be there, and with no evidence of "hot wiring" the pump from PO. It certainly seems to be a solid state relay (potted), but what kind of relay has only three connections (if I'm remembering correctly)? What kind of signal does it get from the igniter box, or does the box just send 12v and the relay connects it up? My guess is that it's more than just a relay in there, but how it does anything with just three wires is beyond me. And what would die if the pump shorts in a normal situation? A fusible link, or the igniter box?
The pump itself was interesting, contacts look decent, plunger a little sticky so I grease it a bit and tried it out, and it acts like a short now. At the two coil wires I get just a couple of ohms at best continuity, but not shorted to the housing. Will all but melt wires if given power. Is this normal for the pump? Maybe a quick hit of juice won't heat the wires if it pulls down and disconnects, but I doubt it. Besides, why would it not pull down the plunger with power in any case? I don't mind getting a new pump, but I want it to make sense first. And if it draws so much power, why did wires not melt earlier on the bike? Maybe I changed something upon disassembly, and it's dead now for some reason. Can anyone shed some light on this stuff, maybe answer one or two of my myriad of qusetions? Thanks!

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post #2 of 10 (permalink) Old 09-28-2009, 08:08 AM
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I think you're referring to the fuel cut-off relay. My son's '84 VT700 had an intermittent problem with the relay. I bypassed the relay and it's been running fine for 5 yrs. Hang in there. Someone more knowledgeable will come along to help.

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post #3 of 10 (permalink) Old 09-28-2009, 09:30 AM Thread Starter
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Relay and pump

Yeah, I may do that when this is solved. I'm thinking that the pump may still be OK (I've heard a few ohms is typical), maybe my voltage to it when testing was too low. I'll try again tonight. Still wonder why I don't have power now at the pump connector on the bike, though. Maybe the cut-off relay is working properly now, and cut off before I got the meter hooked up.

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post #4 of 10 (permalink) Old 09-29-2009, 05:39 AM
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Re: Relay and pump

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Originally Posted by fadingshadow
Yeah, I may do that when this is solved. I'm thinking that the pump may still be OK (I've heard a few ohms is typical), maybe my voltage to it when testing was too low. I'll try again tonight. Still wonder why I don't have power now at the pump connector on the bike, though. Maybe the cut-off relay is working properly now, and cut off before I got the meter hooked up.
My observation is that the pump will pulse a few times when you turn the ignition on to get gas to carbs. Once the bike is running I don't hear many pulses from the pump. My son's problem was an intermittent one. The bike would run for about 12-15 miles and then stall out. After it sat for about 1/2 hour it would restart and run for awhile. Finally found out that the cutoff relay would operate until it reached a certain temp. and then die.

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post #5 of 10 (permalink) Old 09-29-2009, 07:25 AM Thread Starter
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Pumps, etc.

Yes, I've had lots of different electronic devices that fail at temp, but work when cool (have a car doing it now, but don't know which component is the culprit, and the weather is cooling, so it may escape detection til spring).
Tried again to energize the pump on the bench with healthy voltage and current. Wire to the coil went incandescent in a second, now the coil reads open, so it's new pump time regardless. I found one on Ebay that looks to be the same (mitsubishi) with an extra bracket that I can remove, meant for a 1.3 or 1.5 liter civic. I'm hoping the valving inside is OK, but I'd bet they are identical inside.
Still does not answer my "relay" questions. Are both relays the same down there? I can swap them around for diagnosis reasons if so. Still don't know what kind of relay would have three wires.
Please keep the suggestions coming...

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post #6 of 10 (permalink) Old 10-01-2009, 12:23 PM Thread Starter
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Pump deal!

http://cgi.ebay.com/ebaymotors/ws/eB...d=366467683009
That's the pump that I picked out. It's identified as:
1983 83 HONDA CIVIC 1.3 Fuel Pump BECK/ARNLEY 1520735
We will see how it does. I still am unsure how that relay works- three wires means to me that there is more than a relay in there. Anyone know?

I just checked the beck/arnley number, and "rockauto.com" is selling a batch of them (closeout) for $35. I paid about $65 for one. I may buy a spare!

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post #7 of 10 (permalink) Old 10-04-2009, 08:47 PM
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I think that the fuel pump relay is actually a solid state transistor, one pin has system voltage sitting on it (12 volts), the 2nd pin gets its signal from the little blue wire, and then that activates the transistor and 12 volts comes out of the third pin and makes the fuel pump turn on.

If I have time tonight I'm going to test the relay on my 84 VT700C and see if it "looks" like a transistor when I test all three pins.
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post #8 of 10 (permalink) Old 10-05-2009, 10:15 AM Thread Starter
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Transistors- wave of the future

That sounds about right. Thanks. I wonder what kind of signal it gets- if one ignitor box fires the tach, and the other goes to this "relay", and they are interchangeable, it must be some kind of pulsed signal. If it gives me any trouble, I'll bypass it with pretty clear conscience, but it's always good to understand how things work.
I'm surprised tubes_rock hasn't weighed in on this one, but I guess he's just not into devices that don't have a glowing filament.

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post #9 of 10 (permalink) Old 10-05-2009, 09:35 PM
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Well, the basic explanation of this is the signal originates from the two pick up coils that are mounted in the alternator, those two signals are sent to the ignitor boxes which then the yellow wire runs and tach and fires one of the ignition coils, the blue wire tells the fuel pump relay to turn on and fires the other ignition coil.

So yes it is a pulsed signal which would have to start out as a sine-wave coming out of the pick up coils, after that I'm not sure what the ignitor boxes do to the signal, they might just amplify them so that they have enough strength to make the ignition coils fire, or clip them into some kind of square wave.

I did not have time last night to test my relay I'll try again tonight.
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post #10 of 10 (permalink) Old 10-06-2009, 07:42 AM Thread Starter
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Relay

Thanks, no hurry. I still have to mount the new fuel pump, which is larger than the old one. If the relay is not working, I'll just bypass it.
thanks!

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