Please help me :(

[rixskgw]

The ls400 uses the control relay to switch the speeds i have found out, thats why i was saying if someonone could remove the little lid on there control relay and rev the car and tell me how much reving it takes for theres to switch over, that would be a great help

 

[cacrawfo]

Why don't you completely diagnose the problem before blindly replacing components like the ECU etc?

Start by getting the relevant electrical diagrams to fully understand the fuel pump control circuit.....

Why not check the fuel pressure at the rail to see if you are having a low fuel pressure under brisk acceleration....

A quick test to see if the 2-speed circuit is functioning properly is to bypass the large finned resistor with a piece of 14 gauge wire.... that will put the pump in high-speed mode all the time... if your problem is still present you need to look elsewhere.

Carl C

 

[rixskgw]

Nope, its fine after i do that

 

[rixskgw]

so, if when in high speed mode its fine, what could be the problem? the fuel pump?

 

[Zuffen]

No if the pump runs on hi speed it is fine.

If the car runs OK when you by-pass the resistor then you have a problem in the speed control area.

One simple solution would be to run the car for a week or so on hi speed. If all goes OK and you don't mind the pump running on hi speed all the time, put up with it. Note the pump will wear out faster.

That gives you the option to repair the problem in your own time.

 

[rixskgw]

I dont understand what else could be wrong with the speed control... i have replaced what i thought was everything that controls it....

 

[Zuffen]

Why not take it to your local Lexus dealer. It would have to be cheaper than replacing half the electronics in the car.

 

[cacrawfo]

I sais it once before, you need to get the wiring diagrams and fully understand the speed control circuit.... If after that you still do not fully understand the circuit, how it operates, and how to diagnose it, you should give up and take the car to a profesional....
That said, I think the problem is at your resistor.... By bypassing the resistor at the connector, you got the car to run correctly right? That tells me that all the relay connections etc are all OK, the car was commanding the fuel pump on via the resistor box. So when you add the resistor box back into the mix, it stops running correctly...... why not replace the resistor box? Also make sure the connectors all look good, are not burned up, corroded, etc...

It is remotely possible that the fuel pump is getting bad, and does not want to run at lower speeds.... but the resistor box is a lot easier and cheaper to replace than a fuel pump, so I would try that first....