Hi all,

I have a 1990 LS400 and have temporarily worked around a surging/bad idling problem by bypassing the fuel pump relay resistor. I have been looking for a replacement resistor on the usual websites and can't seem to find a replacement. The part number is 23080-50010. These are available (with slightly different part numbers) for other Lexus models. I don't know if the newer resistors are compatible and after trying a newer one the problem persisted.

Does anyone know where I could source a working replacement please?

 

Try using 2 head light bulbs instead of the resistor in case you can't obtain it. 2 bulbs have to be connected parallel. Some heat comes out from bulbs and you have to be careful for that. The temperature reaches higher than 100 degrees C.

 

Hi Yamae,

Maybe I could connect daytime running lights permanently

So if I connect headlights does this mean the pump is always running at lower voltage? I thought the resistor was there to vary the resistance based on load and not just to keep it low.

Thanks

 

That is how it works lower voltage means lower speed. A resistor creates a voltage drop across it and the same across the fuel pump. In essence it becomes a voltage divider.

 

The ECU only sets 2 modes, a high and a low. The high mode is performed supplying full +B to the fuel pump bypassing the fuel pump resistor. The low mode is performed by using the resistor limiting the current. The resistance is constant and is 0.73ohm. It does not vary. Strictly to say it varies some depending on the temperature but the value change is less than 0.1 ohm.

2 head light bulbs organise the resistance about 0.75ohm. You may think it's strange and the value should be more than that because a bulb has a resistance about 3ohm when it is applied 12.6V. It s true that it shows that much when working at 12.6V. But the resistance of a bulb is not constant. It varies a lot depending on the temperature. For an example, at 25 degrees C, it shows only about 0.3ohm which is roughly 1/10th.

When it is used in series with the fuel pump, it shows about a half of the resistance compared with the operation at 12.6V. In that case the current is limited and the heat is also limited. Thus the resistance of a bulb shows around 1.5ohm each when used instead of a fuel pump resistor. There are 2 bulbs and the total resistance is a half of it which is 0.75ohm. It is quite close to 0.73 ohm. Now you see why 2 head light bulbs can be used instead of the resistor. But be sure to prepare for the heat coming out from bulbs.

 

Thanks Yamae,

I'll see about connecting the bulbs, just have to find a way to protect everything from the heat.