naluloa

Hi guys,

So my fuel pump is old and hasn’t been changed. When I fill up gas it would take 2 tries to start (the first start would die out) and my air fuel trims were very lean. So I figured might as well upgrade to a Walbro.

So that’s what I did. I pulled the old fuel pump and put the Walbro in. Granted I had to solder the old wire that went to the old fuel pump to the new Walbro pump’s harness/plug.

I started it up after buttoning up the fuel tank, and voila! It started and idled just like normal after cranking for a few seconds.

So I go about my day relaxing at home. Then o get hungry and decide to eat out. Next thing I know, my car is cranking again, which I thought was weird because fuel pressure should already be built up. So it cranked for a few seconds and started, only this time it started bogging HARD. My door was also open and the courtesy light in the door was flickering. So that makes me think the fuel pump is drawing large amounts of current intermittently. I soldered the wires together after twisting them together so I feel like there shouldn’t have been anything wrong electrically..

After holding the accelerator to keep it at about 1000 RPMs, I decide to run my scanner and see what I can get out of it. Surprise surprise, oxygen sensors are outputting < 0.01 volts.

I took my car for a drive since the idle steadied out at about 600 RPMs, but the whole drive my car would not let me accelerate. Any input to the throttle was met with VERY rough combustion and shaking. So I’m thinking my car is in limp mode right now.

I really don’t know what to do. Others have replaced their fuel pump with Walbro and said it was a plug n play and seemed to have no issues. So I’m really wondering what went wrong. Did I toast my O2 sensors? How would that even be possible from just replacing a fuel pump? Should I have reset my ECU by disconnecting my battery? Would that have saved my O2 sensors? I’m thinking my O2 sensors might not even have been affected but my scanner has me worried that that’s the case. Anyone done a fuel pump upgrade?



The OEM fuel pump mounting piece had a connector with 3 wires: 2 black, 1 blue/green, but the 2 black were terminaled into 1 black wire. The Walbro pump connector only had a red and black. So I figured hey, all I need to do is solder the red wire with the blue/green wire, and the black with the black. So that was how I soldered it. Google says rough idling after a fuel pump replacement is usually due to wiring, but I don’t see how I went wrong when I soldered the red to the colored and the black to the black. Below is the OEM pump harness with the blue/green wire and the 2 black wires in 1. I also put the Walbro pump I installed, which in the picture, shows the red and black wires.

naluloa

So I disconnected the battery overnight to see if resetting the ECU would fix everything. Now the car won’t idle at all. The car just instantly dies after it spins up. Applying throttle doesn’t even keep it alive. Not sure what the issue is.

naluloa

Update: I ended up removing the fuel pump again.. disassembled it, and put a piece that I threw away, back where it was on the old pump, but on the new pump. No more issues. Ha ha ha...

If you decide to upgrade to a Walbo on the GS 400, the pump you get may have a different top than the original pump. The Walbro that I got had a ledge near the up-tube on the top. On the original pump, there was no ledge so the snap ring sits flat at the bottom of the up-tube. On the new pump, the ledge doesn't allow the snap ring to sit at the same level (it makes it sit higher), so the gap where the o-ring is supposed to go is very small. Anyway, I just shoved the snap ring with the o-ring on it and the plastic piece above the o-ring, up into the fuel filter. Heard the snap, and she was good to go.

Thankfully my soldering job wasn't the issue because I cut the wires a lllllittle too close to the junction of the ground and negative wire.

Car is ready to receive a manual trans and supercharger now I don't think the GS 400 needs injectors for a SC, but I could be wrong.

CurlyG

The only issue that comes to mind is the OEM fuel pump is controlled by 3 voltages: it runs at low, medium, and high pressure, depending on demand. If you remove the rear seat bottom, you can hear the motor pitch change as your drive. I had to replace my fuel pump in my 2000 GS400 when I bought it in 2021.