no power to fuel pump

[DeanR]

Need to run my '91. It's been a year or two that it's been sitting. With no fuel tank (it's been empty and in the house) and drained carbs.
Fuel pump is not starting with the key, runs fine when jumped. Wired connections all look ok. Where should I look?

 

[Uncle Phil]

Fuel pump relay?
Dumb question - you checked the ground and the hot to make sure both were good (meter or test light)?

 

[DeanR]

Fuel pump relay?
Dumb question - you checked the ground and the hot to make sure both were good (meter or test light)?

Not a dumb question for this electron dummy. Most times I use my multimeter, I have to be told how to, including now. Electricity stuff just never quite sinks in.

Is the fuel pump relay one of the three up there on the right side of the cowl stay?

 

[Uncle Phil]

Is the fuel pump relay one of the three up there on the right side of the cowl stay?

I believe that is correct -

 

[Ron]

Does the bike start and run if you run a hot wire to the pump? Don't worry about overloading the pump, it runs all the time when the motor runs.

 

[DeanR]

Which of the three relays (if any) is for the fuel pump? I think at some point I've made a note of what each relay controls, but I can't find it.

I can do a timing belt but electrons and the multimeter remain mysterious. I do have a test light, but never sure how to use that either.

 

[dwalby]

Dean,

the fuel pump relay is an expensive electronic version, because its controlled by the CPU using digital logic voltage levels rather than 12v, so don't try to use jumpers, etc. on the relay itself you might blow it up.

the service manual shows its location, but its on a different side depending on STD or ABS model.

 

[Uncle Phil]

The diagram I gave should be for the standard and it is number 8 as I noted at the bottom of the picture.
I've had to replace one before to finally fix a fuel pump issue.

 

[DeanR]

I didn't see the fiche you had posted until now Phil. I believe I have another no.8 part that I can swap in.

Yep, expensive Doug !

 

[kerbside]

In June i hot wired ( 5 amp aux switched output) my pump in S. Dakota and 8,000 miles since with no issues. Easier than getting at the relay on an abs11 bike.

 

[DeanR]

Well I did the relay swap (assuming the spare is in working order).
No luck.
Gut feeling is this is something really simple.

you checked the ground and the hot to make sure both were good (meter or test light)?

How do I do this? With either my meter or test light.

 

[Uncle Phil]

With the key on - see if the 'hot' wire shows any current by grounding the other tester wire to a known ground (like the battery ground post).
For the ground check between the battery hot post and the ground wire for the fuel pump.
In both cases, the meter should show voltage or the test light should light if they are good.
The value of the meter is you will see how much voltage you are getting (I usually set the 'base' setting to 20 volts on a meter).

 

[DeanR]

13.7 at the fuel pump connection. Would this imply that the number 8 (fiche) relay as well as the spare relay are both bad?

Interestingly, the test light comes on slowly and is quite dim at the fuel pump.. When at the battery it is bright and immediate.

 

[Uncle Phil]

So you've got 13.7 at the 'hot' wire that goes to the fuel pump?
What about the ground wire?
You should be getting the same there (though the hot lead would be at the battery and the ground connection would the ground wire at the pump).

 

[Andrew Shadow]

Interestingly, the test light comes on slowly and is quite dim at the fuel pump.. When at the battery it is bright and immediate.

Knowing the exact voltage is a useful test in diagnosing. Also testing with a test light is required for the above reason. You can easily have full voltage but not enough current flow to power the motor due to a bad connection in the circuit somewhere. The volt meter will still register full voltage, but the test light will burn dimly indicating a problem.

As reference test, connect the test light directly to the battery positive and negative posts so that you will know what your test light looks like when it burns at full brightness.

Disconnect the wiring harness from the fuel pump.
Connect one end of your test light to the fuel pump connector 12V+ terminal, and the other end to the fuel pump connector 12V- terminal. This tests both the 12V+ and 12V- sides of the entire circuit all the way from the start to the fuel pump connector at the same time. The test light should burn as brightly as it did in the reference test. If it does, the electrical side of the fuel pump wiring is probably not at fault. Check the condition of the connection between the wiring and the fuel pump, and the fuel pump itself.
If it burns dimly, there is a fault in either the 12V+ or the 12V- side of the circuit.

With the wiring harness still disconnected from the fuel pump;
To test the 12V+ side of the circuit, connect one end of the test light to the battery negative post, and the other end to the 12V+ terminal of the fuel pump connector. The test light should burn as brightly as it did in the reference test.
To test the 12V- side of the circuit, connect one end of the test light to the battery positive post, and the other end to negative (ground) terminal of the fuel pump connector. The test light should burn as brightly as it did in the reference test.
If the test light burns dimly when testing either the 12V+ or 12V- negative side of the circuit, that is the side of the circuit that you need to investigate.

Because you wrote that the light comes on slowly, that indicates that there is a problem with the relay circuit. You tried another relay with the same result. While it is possible, it is unlikely that you have two defective relays. Assuming it is not the relay, your next step would be to test the circuits that trigger and feed the relay at the relay connector using the same method as above for each wire. You can also jump the wires at the relay. This eliminates the relay, so if the fuel pump works you will know that the wiring from the relay to the fuel pump are good.
You will need a wiring diagram to know which wire is the supply, which is the trigger wire, etc..

 

[kerbside]

the fuel pump relay is an expensive electronic version, because its controlled by the CPU using digital logic voltage levels rather than 12v, so don't try to use jumpers, etc. on the relay itself you might blow it up.

Have replaced a couple of pump relays and assume I do not have two relays with faults. Pump power is now direct, no relay, and is fine but would love to find the problem.
Apart from checking connections on all the relay wires going to the CPU, pump and battery, any way to test/measure the relay and the relay inputs?
Had replaced the CPU a few years ago when troubleshooting what I now assume to be an intermittent loss of power to the fuel pump thru the relay - I added at the time an LED light connected to the pump power lead to give me indication of loss of pump power.

 

[dwalby]

The service manual doesn't seem to go into any discussion of the fuel pump relay in the fuel system troubleshooting section, but here's a wild guess.

In the attached screenshot the blue, and yellow wires come from the CPU. From the ignition coils on the right it appears that the blue wire triggers for cylinders 2/4 and the yellow wire triggers for cylinders 1/3. It appears that the square boxes are the ignition coils, and the boxes with arrows are the spark plugs. I'm not sure exactly how the ignition coils are constructed, but it appears to trigger off the blue/yellow wires (I'm guessing that's at CPU voltage levels), and energizes the coil primary with 12v via the black wire. The black wire carries 12v from the bank angle sensor relay (not shown in diagram, but visible in the full wiring diagram picture) and when the blue wire triggers the fuel cutoff relay, the black wire energizes the red wire with 12v to the fuel pump. The green wire is ground for the fuel pump. The reason I'm guessing the blue and yellow wires are at CPU voltage levels is because from reports here that's how the fuel cutoff relay works, its not a regular 12v automotive relay, its something called an SCR.

I'm not sure what voltage you'll find on the blue and yellow wires, if its digital logic levels it will be 5v or less. But, because its pulsing rapidly, you may get a weird voltage reading from a multimeter in DC voltage mode because its not a continuous voltage level. Try both AC and DC settings and see if one works better than the other.

You won't hurt anything by just measuring the voltage at any of those wires with a multi-meter, but if you tried jumpering a 12v supply voltage from the battery into the blue line that expects the CPU logic level in the relay, it would probably fry the relay if its a SCR relay.

another failure point could be the bank sensor and/or the bank sensor relay which provides the 12v voltage supply on the black wire. If you don't have 12v on the black wire, then the problem is further up the path in the bank angle area, or the 12v path to the bank angle sensor.

All guesswork, try at your own risk.

 

[DeanR]

Should be getting back to my problem shortly. Put off due to the stupid hot garage and my world class procrastination.

 

[Ryan_B]

So, backing up to your first post:

Fuel pump is not starting with the key, runs fine when jumped.

I would think that statement points to a bad battery or a loose connection at the battery terminal. If it is starting and running just fine with external voltage (a jump), then there shouldn't be any issues with your wiring, relays or components. Everyone is giving you advice and test procedures based on the assumption that you have a working/good battery. A loose battery connection will sometimes give good voltage, but then drop to nothing once any amps are pulled. Normally, this is most noticeable on a starter that draws a lot of amps (it will just "click" once and never turn the starter).

Can you confirm that if jumped there are no issues, and it will remain running once the external battery is disconnected? If that is the case, look closer at your battery connections and possibly take your battery in to any auto shop for a test.

Ryan

 

[Uncle Phil]

When you 'jump' the hot wire on a ST1100 pump, you are bypassing all relays, circuits, etc.
I would bet he jumped off the bike's battery.
The key is does 'runs fine' means the bike or the pump or both.