Toyota soarer fuel pump voltage control

[dirtydoogle 383]

Right, I am designing a replacement for a fuel pump ecu from a toyota soarer [uzz3* and jzz3* series, same as a jza80 supra and jzx8* chaser]. Basically it is a switching device that switches the voltage out put from 12V [engine cranking and haerd throttle/load situations] to 9V [cruising, idle/low load and rpm].

The original unit has a sender/signal wire from the ecu, obviously to trigger the voltage regulation. This system is prone to dying and nobody seems to have designed a replacement part. All I am having trouble with is deciding what kind of switch to use. It obviously needs to switch when a pre-determined current passes through the signal wire, I have thought of a SMPS [switched mode power supply] or going with a triggered switch [Transistor? Circuit opening relay? etc] that will bridge the 12V circuit and go through a .75 ohm ballast resistor.

Pics may be a wee bit big due to detailing. Attached is my hoary microsoft paint idea, but I can't decide what switch to use! Also a schematic for the original system.

Any ideas/advice would be cool thanks.

Edited June 4, 2010 by Duckeater

[dirtydoogle 383]

Problem sorted, low voltage SPDT relay.

Pharque I'm good

Look out for pic sizes.

Hopefully this could help somebody else?

Edited June 4, 2010 by Duckeater

[jochen 4]

Problem sorted, low voltage SPDT relay.

Pharque I'm good

Look out for pic sizes.

Hopefully this could help somebody else?

Your circuit has an inherient unreliability in it: the fuel pump relay is switching the power always.

Wire it like this

+12V--------------[resistor]------[pump motor]------ground

And then have the relay simply bridging the resistor. You'll get less contact sparking and greater reliability, because the resistor is in circuit during the switching time of the relay

Which is the same as connecting relay contacts 30 and 87 on your own drawing

Edited June 4, 2010 by jochen

[dirtydoogle 383]

Your circuit has an inherient unreliability in it: the fuel pump relay is switching the power always.

Wire it like this

+12V--------------[resistor]------[pump motor]------ground

And then have the relay simply bridging the resistor. You'll get less contact sparking and greater reliability, because the resistor is in circuit during the switching time of the relay

Which is the same as connecting relay contacts 30 and 87 on your own drawing

Thanks mate, I didn't think of that! I'll modify the diagram.

I've run into a problem though, turns out the signal is not a constant voltage, the signal is a solid 5V when 12V [100% duty cycle] is needed at the pump, when "9V" is needed at the pump the signal is 5V at a 50% duty cycle, not like 2.5V as common belief dictates. This effectively tells the fuel pump ecu to cut the fuel pump down to around 75% duty cycle...so I have to figure a way of translating the 50% signal into a 2.5V or, ideally no signal at all. I've been looking at the effect of a step down buck converter, but, I don't think that is going to work. Perhaps some clever trickery with some SCRs? I've never worked with PWM before so this is all new to me.

Any suggestions?