I have a 95 legacy that is having intermittent fuel pump issues. Replaced and tested pump. Works. replaced pump relay but may not be the correct one. I hear it open when the ignition is turned on. Test light shows little power at the pump. At times it will start if it sits or if I unplug the pump and plug it back in. this issue is driving me crazy.

Welcome to the USMB.

 

When you were using the test light, did it tell you how much voltage was at the pump?

 

The thing to note is that the ECU supplies voltage to the pump for a few seconds to prime the fuel system, and then shuts off unless the engine is cranking/running. So testing the voltage can sometimes be tricky. There should be a green diagnostic connector under the dash that you can connect. This will put the ECU in a diagnostic mode, and it will cycle all the relays, including the fuel pump. This will allow you to check for proper voltage.

 

There is a connector for the fuel pump under the passenger side rear seat that can sometimes become corroded and have high resistance which causes issues with the fuel pump. If this is a problem, you can simply use another type of insulated spade connector to replace the stock one.

The pump relay actually "closes" the contacts to send power to the pump.

 

Check the power at the relay contacts to make sure full power is getting to that point and use chassis ground as the reference. If that is ok then check the power side of the connection at the pump to see if you have full power there also. If you don't then there is a bad wire connection between those points. If you have good power there also then the problem may be with the ECU if the ground for the pump motor runs through it.

I've seen a couple with burned contacts at the fuel pump connector. Is there brown marks on any of the plastic surrounding the pins of the fuel pump connector under the access panel in the back?

To narrow it down more, you could maybe rig up some sort of text jig that plugs into the cigarette lighter to power the fuel pump directly. That would bypass the relay and its controls. The cigarette outlet I think is hot in acc and run.....but not sure about start.

 

There were some posts in the past where people found the transistor on the ECU that drives the relay had gone flaky, so they replaced the transistor, but I think then it just doesn't work at all, not intermittently.

 

What made you think there was something wrong with the fuel pump to begin with?

There were some posts in the past where people found the transistor on the ECU that drives the relay had gone flaky, so they replaced the transistor, but I think then it just doesn't work at all, not intermittently.

 

The transistor that went bad inside the ECU was tied to another transistor that controlled the ground side of the wire tied to the pump motor. You are correct about it the trouble being a constant failure.

I have just been through my car trying to fix a similar problem. I had driven 500km the other week and not a single problem, get home after 28km along a dusty track and leave it outside for a while. Now it does not start after turning over and over again.

Fuel pump = fine

Fuel relay = fine

 

But tested the connections and there is no power getting to the relay or the pump. Perhaps there is a problem with the wiring on the bottom of the car where it enters under the passenger seat. This is my next task; to see if the dust has affected the wire underneath.

 

Does anyone have an idea to what could be causing this problem other than a wire issue? (Speaking to a man today, he thinks that the onboard computer could be confusing itself due to the battery going flat and then being recharged)

 

much appreciated

Harry

I ran a new wire from the relay to the fuel pump. This has solved my problem completely. After testing the relay I determined that I had power to the relay and coming out of the relay, but it was not getting to the pump. Ran a new wire, problem solved.

Glad you got it fixed. Thank you for reporting back the solution!