Fuel Relay issues

This past August my 4th Gen died in the parking lot of my hotel in downtown Buffalo. It seemed like a fuel issue, and confirmed the float bowls were empty and I could not hear the fuel pump come on.

Well the same thing had happened on the Mass pike the previous year, but I was getting buzzed by semis at 70mph and it was so noisy I did not figure out the problem until after I got towed to my brothers in NH. I figured it out and made a jumper and put it into the connector and drove back to Maine no problem. I replaced the relay and all was good.

Well I had the jumper in with my tools and quickly got the bike running, dropped my niece off in Erie then drove back to Maine. I ordered another relay (shindengin) and went to install it this week only to find the pump would not come on with the new unit but ran fine with the Jumper wire.

So my question is, is there a way I can test the new relay? I'd like to be sure that it is in fact the relay and not something else before I return the unit.

I do have a decent digital multimeter but my electrical knowledge is pretty basic.

Thanks for any guidance or advice.

Relays can seem like a bit of black magic - but they're basically an electrically actuated switch.  I try to think of them as a normal rocker switch (could also be the ignition switch) with a coil that activates the rocker instead of your hand.  In the diagram below (plenty on line with a search), the numbering of the terminals is pretty typical, though from Japan it could be different.  Power from a switch (like a headlight switch) comes across terminals 86/85.  When that happens, the switch inside the relay is electrically triggered (closed) providing usually an audible "click", and then with the switch closed power flows across 30/87 to the load ("Device"), in the example headlights (or in your case, fuel pump) to ground.  To test it, place 12v across 85/86, see if there's a "click", and then using the meter see if the 30/87 has continuity.  As long as your meter has clips to attach to the terminals you should be able hold jumper wires to the power source and ground.   A Japanese sourced relay may not have the same terminal numbering, but the concept is the same.  You can check it installed on the bike by backprobing the terminals (a paper clip works for that), but be careful that you know which terminal is which - you don't want to jump the wrong pair.  In the diagram, below, terminal 30 always has power to it, so that's also good to check before deciding the relay is bad. 

Relays are pretty reliable, though they can get sticky with age - sometimes a tap on them will make them work.  Something else to consider is that possibly your original relay is still good - check it, too - and by bypassing it to the fuel pump you are possibly unknowingly bypassing a fault further down the circuit beyond the relay.  In other words, the relay is sending power to the pump, but something between the relay and the pump is faulty.  In the diagram it would be a fault between "87" and "Device".  Since the pump runs by jumping it, it seems reasonable that it's grounded properly.

That's probably clear as mud, but I hope it helps. 

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That's all good stuff Cogswell but isn't FromMaine referring to the Fuel Cut Relay on a 4gen?

Looking at the circuit diagram this is a special 3 pin relay that is energized by ignition pulses, then sends power to the Fuel Pump. So it doesn't appear to be the normal relay coil arrangement, possibly electronic! Not too sure how you would test this relay outside of the bike.

I believe some 4gen owners just link the relay out and don't bother with it!

Sorry, I have no experience with a 4gen.

Cogs:

Looking at your diagram it looks like a 4 pin relay. Lots of tutorials in Youtbe on these as I've read quite a few. Many of these type you can take the cover off and see the contacts. Mine is not like that.

As you noted I to had my suspicions that the original might have been fine when I plugged the new one in and got no response, hence my wanting to see if I can test it.

Grum:

As you noted the relay on my bike is a 3 pin, and yes I think it is electronic as its potted in Epoxy unlike the other type relays.

I did not know it was powered by ignition pulses, which makes me think I should start chasing the ignition wiring and checking my connections there before proceeding else where. I did ride the bike for 2 months with the jumper wire without a problem, but if I do have a wiring issue now is the time to rectify it, its already snowed twice here so riding is effectively over, plus I don't want to be fixing it by the side of the road 1,000 miles from my garage next year. 🙃

Thank you both for your timely and helpful responses!

Also the Service Manual doesn't offer much in the way of description. It just offers a continuity and voltage check of the three wires to the relay.

Its operation though is to simply disable the fuel pump if the engine is not running. 

Grum:

Yes, I've read both the Clymers and Honda service manuals, both focus on the fuel pump itself rather than the relay, which is why I hoped someone here had figured out a way to test them.

It is a safety feature, but I guess if you don't drop/crash your good to go...……......I cant be trusted to not do either though. :^)

I just got back from the garage and had a look with my flashlight, 1 wire to the fuse box, 1 to the Spark unit and 1 to the pump. I'll tear into it tomorrow as its after midnight and 1C with slushy rain and I'm feeling wimpy. BTW I did find my wiring diagram, should have looked at that first.

Thanks again mate

BTW - this is special relay that apparently has some circuitry inside that keeps it ON between grounding pulses from ignitor. Probably a capacitor & diode inside to keep it engaged just long enough for next ignition pulse to come along.

What's this jumper you made do? Does it bypass relay and just bridges black to black/blue wire on relay-connector and powers pump any time run-switch is ON?

Here's some simple quick tests with multimeter. Remove relay from connector:

1. key ON, run-switch ON, measure voltage at black wire going into relay connector. What is voltage?

Test relay, use test-leads with alligator clips:

2. connect +12v to black terminal on relay

3. connect ground to red/yellow terminal on relay

4. measure voltage at black/blue wire terminal on relay. What is voltage?

6 hours ago, DannoXYZ

BTW - this is special relay that apparently has some circuitry inside that keeps it ON between grounding pulses from ignitor. Probably a capacitor & diode inside to keep it engaged just long enough for next ignition pulse to come along.

What's this jumper you made do? Does it bypass relay and just bridges black to black/blue wire on relay-connector and powers pump any time run-switch is ON?

Here's some simple quick tests with multimeter. Remove relay from connector:

1. key ON, run-switch ON, measure voltage at black wire going into relay connector. What is voltage?

Test relay, use test-leads with alligator clips:

2. connect +12v to black terminal on relay

3. connect ground to red/yellow terminal on relay

4. measure voltage at black/blue wire terminal on relay. What is voltage?

Yes, the jumper bypasses the relay entirely and provides power to the pump. The pump has a pressure switch and cycles normally.

Voltage at the relay connector is 11.2, my volt meter says my battery has 12.4, so there is a loss. I'll check this out. I'll try again later today when I won't wake the neighbors to see if the voltage increases at the black wire.

Not sure I can get alligator clips on terminals on the relay, have a look at the pic, they are in the white plastic connector that is epoxied into the unit. Probably can sneak some small leads in there if I'm careful.

Many Thanks for your thoughtful response.

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Yeah, it's a tight squeeze. There's little holes on tip of terminals in relay. What I've done in these cases is take some small solid-core wires (20-22ga). Strip about 6mm from end and bend end about 90-degrees. Slide that end into hole in terminal. Reach in with needle-nose pliers and fully bend end back 180-degrees to clamp onto terminal. Repeat for others. Then you've extracted signal from those hard-to-reach terminals to outside and other ends of wires can be measured easier.

That is a large voltage drop for no-load measurement. With current flowing, it may drop even more. Trace black wire backwards from relay-connector and examine all other connectors on way back to battery. might be case of corrosion on terminals that needs some clean-up. 

Thanks, that's a great tip, now I don't have to go out and find the worlds smallest alligator clamps……….🙃

Did not get a chance to trace the wires and check connectors but did start the bike and measure voltage at the black wire while running, and it was 13.4-13.5v. plugged the relay back in and the fuel pump stopped working. Shut it down before I drained the bowls. So I'm thinking its not picking up the feed from the spark box. I'll check that and the connectors for the black wire tomorrow before running a test on the relay.

Many Thanks again.

Isn't that connector just a standard 3-pin "Hitachi" connector (as used all over the bike's wiring loom)?  http://www.cycleterminal.com/110-connectors.html

Maybe a bit OTT to make up a connector just to test the relay, but it is always a good idea to have some on hand with these older bikes.  

Ciao,

JZH

The fuel pump relay on the '97 is not an actual relay; the type with a coil of wire that when power is applied to creates a magnetic field which pulls a metal actuator (the switch) which completes a circuit.

The Fuel Cut Relay (as labeled in the Service Manual) is all electronic.  This "relay" provides the power  for the fuel pump to operate.  The ignition module sends a (return/ground) pulse to the coils and also to the Fuel Cut Relay.  This is what enables the "relay" to provide the power to the fuel pump.

As stated above, the "relay" is a safety feature to shut-off the fuel pump when the engine is not running.

When the jumper was in place, this provided constant power directly to the fuel pump, bypassing the Fuel Cut Relay. (Jumper Black to Black/Blue)

No easy way to test the "relay" by itself. 

But do check-out the R/Y wire at the Fuel Cut Relay to the Ignition Control Module; check the terminals.  You have already verified that power is on the Black wire at the Fuel Cut Relay and that the fuel pump works, so must be a problem with the connection to the Ignition Control Module.... that is my suggestion as to where to look.

There's two possible issues, we we need to do two different tests to see what problem is. Might be both areas are bad.

TEST FUEL CUT RELAY

Bench-test relay as above. This will give 100% verification relay is good or bad.

Solid-state relays are direct drop-in replacement for mechanical types and operate exactly same way.

Replace coil with pnp-junction of transistor and it flips switch same way.

Relay has no idea if ground signal is coming from ignition-coil or from ground-jumper.

TEST IGNITION SIGNAL AND CIRCUIT

The ignition signal is a ground. Digital electronics has three possible states: high, low or open.

Ignition signal on R/Y wire is either open or low. When it's low, R/Y is connected to ground to dump coil.

Ignition circuit provides the ground for relay's coil while black provides power.

If you don't have proper ground coming from R/Y terminal, then that wiring to coil may be bad.

Can test grounding pulses with solenoid-light. https://www.amazon.com/dp/B004FEN84M/ Connect one terminal to black wire and other to R/Y wire at fuel-cut relay connector. Also test for proper grounding pulses by connecting to ignition coil. It may be case of bad wiring and signal is present at coil, but not at relay-connector.

Or test with oscilloscope:

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The grounding pulses are extremely short. If R/Y wire between relay and coil has drop-out like black wire, it's very possible these ignition-pulses aren't long enough to trigger relay and keep it activated. To verify wiring, test signal at ignition-coil itself, then compare trace to one at relay-connector. If they're not identical, wiring is bad between coil and relay-connector. You can replace that R/Y wire end-to-end. Also test other coil's trigger signal with oscilloscope as well.

"Fuel cut relay" is really bad terminology, might be translation issue like "all your bases are belong to us". Before relay can cut power to pump, it must first provide power to pump like any other normal relay. On many bikes and cars, this relay is wired into crank-sensor so that relay doesn't activate fuel-pump unless engine is spinning. This comes from 1992 FMVSS regulation that dictates some safety requirements. Tying fuel-pump operation to engine-speed is one way of satisfying those safety-requirements. Prior to this, you can be trapped upside-down in flipped-over car after crash and fuel-pump can merrily continue pumping and dump entire contents of tank from ruptured fuel-lines onto hot exhaust-pipes!

Lannyl81, 11/16/2020 at 4:07 AM

The Fuel Cut Relay (as labeled in the Service Manual) is all electronic.  This "relay" provides the power as a pulse for the fuel pump to operate.  The ignition module sends a (return/ground) pulse to the coils and also to the Fuel Cut Relay.  This is what enables the "relay" to provide the power pulse to the fuel pump.

Think this needs a little clarification!

The Fuel Cut Relay doesn't provide a power pulse! It provides solid 12v to the Fuel Pump if Ignition pulses are detected at the relay.

The pulsating of the fuel pump is a characteristic of this type of pump.

first time i had that relay fail (1990) i jumpered it and have done the same to all my honda bikes since.  seems a waste of money to buy a new relay to replace one that is known to fail often.