Fuel pump issue

[Sethdc04]

Hey all, I have a 1990 GL1500. Im having issues with the fuel pump power wire losing voltage. The fuel pump works fine when jumped btw. The issue is that the power wire won’t remain energized when it’s connected to the pump. When i unplug the power wire and test voltage, I have 12volts when the bike is in the run position, but as soon as i connect the wire, voltage drops to .5volts. I’m stumped. The ground is obviously good because I’m able to jump it from the positive battery post and using the ground wire that’s connected to the pump from the wire harness.

[DenverWinger]

I know the 88-89 models used a fuel pump relay and the 92 on up drive the fuel pump directly from the ECM. Not sure about 90-91 years. I think they are ECM drive but not sure. Anyone Know for sure?

Troubleshooting this will depend on knowing how the circuit is configured.

[Sethdc04]

Thanks Denver. I thought that too by there is no fuel pump relay on this bike. I ran the troubleshooting procedures and at the step I’m at its saying to replace the ECM, however, i still find it really odd that the wire is energized up to the point where it gets plugged back in to the pump.

[the_big_h]

The multimeter you are using to test voltage draws very little current, so if there is a high resistance in the circuit, you will still see full voltage with just the multimeter, but not enough current will flow through the high resistance to operate the fuel pump. For this reason in many cases a test light is a better tool to use than a multimeter - the test light draws enough current to avoid giving false assurance that the circuit is working.

In this case, I'd suspect the output transistor in the ECU that drives the fuel pump output. It could have had the smoke let out of it, or there could be a bad solder joint. I think I've heard of this being a fairly simple repairable issue, but that might have been on a different ECU entirely.

[MikeB]

If the voltage drops when the load is applied as in re-connecting the wire to the pump, then the power is insufficient to handle the load of the pump. Lots of times this is caused by a faulty or weak connection somewhere upstream of where you are testing. This is indicative of a corroded connection at the 12 volt supply. If the 12 volts is supplied by the ECM, then check the connections at the ECM or the wire that is coming from the ECM to the pump connection.

[Rambozo]

If you do find it is the ECM, there is a repair procedure to change the output transistor in the ECM posted either here or at goldwingfacts.