Troubleshooting, No Fuel Pump Operation Unless Switched To Reserve

[SpecOps13]

This is what's happening with my 89. I've been fighting this for a week now. The fuel pump relay basically controls and directs when the fuel pump operates. There are only 5 inputs / 1 output.

1. A hard ground. (input)
2. Power to the relay when switched to reserve. (input)
3. A ground supplied when the tank is low on fuel. This is controlled by the tank sensor. It shuts off power through the relay from the ignition switch being on and the fuel pump is disabled. (input)
4. Ignition on power to the relay. (input) Enabled, disabled by # 3. and the ignition switch.
5. Tach input signal that enables the fuel pump if certain other signals are present, Ignition on, kill switch to run, kick stand up sensor or neutral light on, bla bla bla.
6. Voltage line to the fuel pump. (output)

It runs when switched to reserve, actually until the tank is dry. If I put the switch to "On" rather than reserve, I can watch the output of the relay to the fuel pump stay steady for 10 or so seconds then fall off to zero volts. The battery reads 12 volts, the input / output of the relay at best is 10.4 volts. It goes up slightly with the engine running... but the relay and fuel pump act the same.

I've measured 3 tank sensors, all were within reason the same. One is in my 94 and that system works fine. I've tried 3 different relays in both bikes. They all work in the 94. They all act the same in the 89. It's driving me Frigging Nuts.

ANY WORDS OF WISDOM, GREATLY APPRECIATED...

Help Me Obi-Wan Kenobi......

 

[MaxMidnight]

I would have thought that if all of the components work out OK then that would leave you with with a wiring issue?

Have you tried running another wire in parallel at each stage of the circuit to see if that sorts the problem?

 

[[email protected]]

Is the low fuel level indicator light in good working order and is the bulb the proper wattage?

 

[PATMAX]

Just think how much better you are gonna feel when you conquer this gremlin too. There is a sticky or thread that addresses this very syndrome as I too was its victim. I think it was posted by Ragin main I think. Let me try to look it up again too. Don't forget to post the fix if you find it.

 

[maleko89]

Am I missing something? I don't see a problem. You say the pump won't run in the on position but it won't until you fill up? I would start by cleaning your reserve switch and measuring continuity at both positions.

 

[SpecOps13]

maleko89: I disassembled the switch and cleaned it. Tank full and the engine won't run with the switch to on. There is no continuity in the on position, the ignition being on supplies voltage to run the fuel pump. :ummm:


Dave

 

[maleko89]

The red/white wire feeds the fuel pump relay when the reserve switch is in the ON position. You should have 12 volts going into the fuel pump relay from this wire. When fuel light is lit, you should get 12 volts coming in from the red/green wire coming from the RES switch when that is switched on RES. Did you try unplugging the fuel sender? It's the two wire connector near your rear brake switch. Should be a green wire coming from it. Another possibility is the gray wire coming from your tach/vboost. This is a safety circuit. The fuel pump automatically cuts when an ignition signal isn't present. This could by why you get a good voltage for a bit and then it cuts off. Try this...drain your carbs and then flip the key on again. You should hear the fuel pump for a few clicks.

 

[SpecOps13]

As is always the case with this bike, let it set overnight and things are different. The name SkullDuggery is being burned into it with every step I make forward.

From the relay:

Black wire to ground continuity, Zero Ohms

Red / Blue: 10.4 volts when switched to reserve.. Goes up with the bike running.

Green: 2.14k Ohms tank full, same as my 94 and it works... Disconnected sensor, no difference with a full tank.

Red / White: 10.4 volts with ignition on. Goes up with engine running.

Brown wires: 10.4 volts when ignition is on. Goes up when engine is running.

Blue: Zero volts when bike is started with fuel switched to on. momentarily switch to reserve and back to on it will maintain battery voltage until bike is turned off. Then the fuel pump will not run when the bike is started again, until you flip to reserve and back to on. Then again it will continue to run until the bike is shut off again...

Here's a thought:
:th_biggun::rocket bike:

 

[one2dmax]

It was discovered that the fuel light must be working for the system to work correctly. I also found out the hard way that the newer clusters are wired just enough different that they are not interchangeable (without moving the harness over) or this same situation will be happening.

Our bike we are talking about worked with the pump in the reserve position thereby forcing the pump on. The on position would never work.

Sean

 

[SpecOps13]

I have an 89 and a 90 dash, neither one allows the fuel pump to work in the on position of the switch. The bulb in the 89 dash is good for sure, I pulled it and stuck a meter to it. Thanx for all the ideas. I'll keep checking things... The bike keeps altering itself but I'll catch it soon.

 

[one2dmax]

The interchange for them is 85-89 and 90-up.

Sean

 

[SpecOps13]

I got to thinking about that after my last answer. Everything in the 90
dash seems to work except the switch problem. The Tach was flaky at times
in the 89 dash but maybe I better swap it back in to troubleshoot...

Thanx for the wake up on that Sean.. 90 did go to digital...
??? I wonder if the dash has been replaced before with a newer one before.
Sure would make it hard to find the problem if all I have are newer dashes.

 

[[email protected]]

You can tell the difference between the early and late gauge pods by the color of the connectors.

85-89 gauges had one white, and one black connector
90-07 gauges had one white, and one red connector

85-89 gauge pod
http://cgi.ebay.com/ebaymotors/85-Y...2925889QQptZMotorcyclesQ5fPartsQ5fAccessories

90-97 gague pod
http://cgi.ebay.com/ebaymotors/91-Y...3437710QQptZMotorcyclesQ5fPartsQ5fAccessories

 

[SpecOps13]

Yup, I have one of each....:confused2uh....
Guess I have a spare for the 94...

Thanx mabdcmb

 

[one2dmax]

The actual clusters can be used by simply swapping the harnesses.

 

[SpecOps13]

I spent 14 Hours workin with the 89 today, accomplished all kinds of good things. I'll write the details of the day somewhere but I'm Toast, Drain Bread.:biglaugh: Lights Out after I write this...

Short story on the dash. I pulled the 90 dash out and noticed as was mentioned, a few wiring changes. Duh on me. I used the 90 outer shell on the original 89 guts. As I said, the bulb was good,,, but the light socket was FUBAR. Although I did manage to fix it. Amazing, I have fuel in the on position and a fuel light when I ground the green line...

Thanks for all the help and support. We Won...
Having all of you here on this forum really helps a lot...

 

[Redbone]

That's great news Dave, I guess it proves that our bikes are geting up there in age.
I'm sure you slept much better knowing this tidbit is taken care of! :thumbs up:

 

[SpecOps13]

Brian (Redbone), I mentally feel great about finally finding the fault. I did so much work yesterday, I almost can't move today.:rofl_200:Being Old Really Sucks.

Later, I'll add this cure and all the other stuff I got finished up yesterday. It'll be on the thread that I'm using to keep track of all the work going into this PITA 89...:biglaugh: SkullDuggery. (Misspelled on purpose)

Dave