Using Xtreme G4+ to control MR2 Power Steering

[AlexLSX7]

I'm going to be fitting an MR2 Electro Hydro Power Steering pump to my car and would like to add a speed signal to the PS Ecu so it is not running at full speed all the time. Can i use a signal from the Xtreme ECU to tell it how fast the car is going so it can be controlled?

[Adamw]

Yes, you can do this - assuming you have a VSS or wheel speed sensor already connected to the ecu.  The easiest option would be to set an aux output up as "speedo out", this gives you some basic scaling settings that I think will be enough to give you decent steering feel Vs speed.

You could also do something more complex if you wanted using a GP PWM set to frequency table, this would give you a 3D table for powersteer effect, so you could for instance not only have a speed input but also add say a knob on the dash to vary steering effort.

[cj]

On both electric and mechanical driven SW20 speedo's, the dash is the source of the speed signals for the entire car (ecu, power steer controller, criuse control etc). On the electronic drive models there is a wire from from the gearbox sensor to the dash, but still a completely separate output from the dash to everything else.

The factory setup has a pullup within the ecu (not sure if 5v or 12v), and the speedo itself "outputs" ground pulses. This means you will need to configure the link ecu to use a pullup resistor on this output circuit, or add one in externally. Safest bet would be to pull it up to 5v to start and if that doesnt make the power steering ecu behave, pull it up to 12v.

The other useful control on these pumps is a pin labelled PSCT or EF1 (Blue/yellow - pin14) on the wiring diagrams - that functions as a kill switch for the power steering - ie in factory config its used to disable power steer when the engine is off to replicate how a hydraulic pump would behave. Leaving this pin floating lets the PS ECU do its thing. Grounding this pin makes the ps ecu disable any steering assist - ie you can set the link to ground an output above 50kph to turn the steering back to manual above this speed.

[Adamw]

43 minutes ago, cj said:

This means you will need to configure the link ecu to use a pullup resistor on this output circuit, or add one in externally. Safest bet would be to pull it up to 5v to start and if that doesnt make the power steering ecu behave, pull it up to 12v.

The aux outputs already have an internal pull up to 12V.  I have run the common W30 "MRS" pumps speed input directly without issue.

[AlexLSX7]

Wow, didn't expect such detailed replies, thanks guy, really appreciate it

My car is an LS swapped RX7 with a TR6060 gearbox.

I have a Dakota box which sends the signal to my speedo which is pretty accurate. Maybe i could use that? The ECU must be getting it from somewhere, potentially there?

[cj]

You'll need to check the wiring in your own car to determine how its wired up. Its likely gearbox > dakota > dash + ecu, but you can set these things up many different ways.  Is it the factory dash? the link acceptable input range is in the same ballpark as what most 90's dash's expected, and that TR6060 probably outputs a much higher frequency being quite a new gearbox, so i'd guess the dakota box is used to drop the frequency to something the dash and ecu can both use. Conveniently, most 90's japanse cars used the same number of pulses per km for their dashes, so you can probably just splice into the dash+ecu speed signal and run an additional wire to the speed input on the steering ecu.

Get out your multimeter and figure out which wires connect to where so you can be certain.

You've got 3x options

1) use the link as a frequency converter and run a new speed output wire from link > steering ecu

2) connect from one of the dakota outputs to the steering ecu

3) if youve already got the right frequency running into your dash you can add a wire to this so its connects to the steering ecu as well.

 

Only #1 will give you personalisable control over the level of assist. The other 2 will both take the real speed and feed it to the steering ecu so it will follow the factory speed vs assist calibration. 

[AlexLSX7]

24 minutes ago, cj said:

You'll need to check the wiring in your own car to determine how its wired up. Its likely gearbox > dakota > dash + ecu, but you can set these things up many different ways.  Is it the factory dash? the link acceptable input range is in the same ballpark as what most 90's dash's expected, and that TR6060 probably outputs a much higher frequency being quite a new gearbox, so i'd guess the dakota box is used to drop the frequency to something the dash and ecu can both use. Conveniently, most 90's japanse cars used the same number of pulses per km for their dashes, so you can probably just splice into the dash+ecu speed signal and run an additional wire to the speed input on the steering ecu.

Get out your multimeter and figure out which wires connect to where so you can be certain.

You've got 3x options

1) use the link as a frequency converter and run a new speed output wire from link > steering ecu

2) connect from one of the dakota outputs to the steering ecu

3) if youve already got the right frequency running into your dash you can add a wire to this so its connects to the steering ecu as well.

 

Only #1 will give you personalisable control over the level of assist. The other 2 will both take the real speed and feed it to the steering ecu so it will follow the factory speed vs assist calibration. 

Awesome, thanks so much for that, it is really helpful