Power steering weight mod

Hi

Just wanted to share a mod I just did the other day, after having stumbled across it a long time ago on supraforums. Now, I've modified my supra towards what I thought it would have been, had it not been developed to be able to be a runaround/DD/shopping/ show off car for all minds if people. In short making it a bit more focused, but with a heavy lean in OEM pars. So TRD brakes, pedals, anti roll bars, CW suspension, new OEM suspension arms all round, repo holstered OMP comfort sports seats, strut braces and so on. I've always wanted for a bit more feel in the otherwise direct steering, but haven't really thought it possible besides the suspension and wheel upgrades. So I settled for working on less assist from the PAS system.

I thought that would be a nice addition, giving a more modern and less compromised feeling to the car. As it turns out, it more than payed off. After having installed an 8 ohm, 50 watt resistance between the PAS ECU and the solenoid in e engine bay, I now have a more weighted steering, but also seem to be having a lot more feedback from the road, possible due the less "obstruction" due to the aid of the PAS.

If anyone is interested in doing this, I can give more specific details, but in short I found two ways of doing it, one is simply to solder the 8 ohm (or 10, if you want even less intrusion from PAS) 50w resistor in in the limegreen wire with a black line going from the PAS ECU. This I found rather difficult to get to, even if you can follow the wire to the nearby junction point. Also, I don't like cutting in the factory harness.

I found it way easier to buy the two plugs from Mr. T (90980-11002 & 90980-11003), getting the pins from an old wire harness and then soldering in the resistor between the two. These two plugs the fit directly in where the signal goes to/from the steering rack in the engine bay below the heat shield of the turbos. Click, and take a drive. That's it. Only thing is that I would recommend that you do some nice soldering and waterproof the soldering as it will sit close to the ground and possible spray.

I really do recommend this to everyone who doesn't require little-finger light steering but want some actual feel. I only need to test this on track, but that will have to wait for next season

Sounds interesting, and addresses one of the Supras few flaws.

I'm interested in this, can you post up info? Any photos, ECU pin numbers, links to get the resistors, that sorta thing?

For a moment there I thought you were going to redirect the aircon into your engine bay and I was gonna win another imaginary car

i'm interested in this, can you post up info? Any photos, ecu pin numbers, links to get the resistors, that sorta thing?

 

For a moment there i thought you were going to redirect the aircon into your engine bay and i was gonna win another imaginary car

I'm interested in this, can you post up info? Any photos, ECU pin numbers, links to get the resistors, that sorta thing?

 

For a moment there I thought you were going to redirect the aircon into your engine bay and I was gonna win another imaginary car

For a second I thought about that thread too!!

Interesting mod, I'd have to drive one with this mod first to make up my mind but it does certainly sound interesting!

I know little about electrics/electronics but is there perhaps a chance you could put a variable resistor in so you could have an in car adjustment?

I know little about electrics/electronics but is there perhaps a chance you could put a variable resistor in so you could have an in car adjustment?

Good idea you could have say a few setting such as;

Track setting

Motorway driving

Spirited driving

wafting setting

I know little about electrics/electronics but is there perhaps a chance you could put a variable resistor in so you could have an in car adjustment?

Fiat 500 has a similar setting, has a button on the dash think it's called 'city steering' I nearly flipped the car using it in that mode

Fiat 500 has a similar setting, has a button on the dash think it's called 'city steering' I nearly flipped the car using it in that mode

Ha ! My friend use to have a punto and it had this, made the steering so light he nearly ripped the steering wheel off !!

The Mrs fiat stilo has city mode, she uses it when parking. You can literally steer with 1 finger

I know little about electrics/electronics but is there perhaps a chance you could put a variable resistor in so you could have an in car adjustment?

I was thinking along these lines too when I read it, and although the resistance part of it isn't a problem 50 watts is a fair bit of power to use a simple pot or even a wire wound rheostat to control. However it could be done in other ways i.e. a simple series transistor regulator circuit or a voltage reg ic with the reference leg jacked up via a switch or adjustment, but just need to know a bit more about what that leg of the ecu is actually seeing, i.e is it a simple DC voltage or pulsed or what? I guess i could scope it out on my car given time.

I was under the impression the PAS solenoid was Pulse Width Modulated to vary the assistance ratio. I have no idea what adding a resistor to the system would do other than lower voltage/current.

Lyndon.

Unplugging the connector on the steering rack pretty much does this. I had it for a few weeks when I was getting work done and the person had left it disconnected. I didn't like it for about town, but I can definitely see how it would be advantageous on a track.

If you want to "suck it and see" without soldering or interfering with anything simply unplug the 2 pin connector on the drivers side just beside the turbos, it's easily identified as it goes to the steering rack.

Poached to tech and given a more descriptive title

More info on this would be great.

I was under the impression the PAS solenoid was Pulse Width Modulated to vary the assistance ratio. I have no idea what adding a resistor to the system would do other than lower voltage/current.

 

Lyndon.

I guess it would lower the power sent to the solenoid, making the solenoid slower to respond and thus lower the pulse rate, giving less assistance?

I'll happily post up more info on the mod. However, I'm at the nürburgring right now with a slow internet connection. I'll do all I can on Sunday.

To shortly reply, it cannot be compared to just plugging out the connectors, as that is intensely more weight to work with, but it might give you an idea of it, if you get a bit up to speed. Without PAS, the supra is impossible at a standstill to low speed.

I can't vouch for other possible solutions with the same possible result, as I have no real in depth now ledge of the type of signal in the system or the result of different watt ratings of resistors.

In the mean time, here is the original thread from supraforums:

http://www.supraforums.com/forum/showthread.php?663406-HOW-TO-reduce-Power-Steering-Assist&

Remember, in stead of cutting in the wire harness, I created a small addition to the harness to plug directly into the plug on the steering rack.

Let me know if further documentation is needed

I'll happily post up more info on the mod. However, I'm at the nürburgring right now with a slow internet connection. I'll do all I can on Sunday.

 

To shortly reply, it cannot be compared to just plugging out the connectors, as that is intensely more weight to work with, but it might give you an idea of it, if you get a bit up to speed. Without PAS, the supra is impossible at a standstill to low speed.

 

I can't vouch for other possible solutions with the same possible result, as I have no real in depth now ledge of the type of signal in the system or the result of different watt ratings of resistors.

 

In the mean time, here is the original thread from supraforums:

http://www.supraforums.com/forum/showthread.php?663406-HOW-TO-reduce-Power-Steering-Assist&

 

Remember, in stead of cutting in the wire harness, I created a small addition to the harness to plug directly into the plug on the steering rack.

 

Let me know if further documentation is needed

Have you unplugged the connector from the steering rack? It doesn't do away with the power steering at all, it merely does away with the low speed aspect of it, thus giving you motorway speed steering throughout the range.

When mine was off, the car was fine.. I used it for quite a while till I figured out the issue. There was no issue manoeuvring or driving the car, it just wasn't fingertip light like it was previously.

Maybe an interesting read regarding Powersteering: http://www.autospeed.com/cms/article.html?&A=110778

Finally I will give this a go hated all 4 supras ive had far to light on the pas , unplugging 2 pin wire as some have mentioned the pas can this damage anything

As already said, unplug it.

This works fine, we have done it on Jay's car and he prefers it.

If you don't like it plug it back in

Sounds simple enough for my abilities I'll give that a go next week hopefully

Ok, so in continuation of my previous description, here is a bit more info:

The point of the mod is to give more weight to the supras steering , even resulting in more of a feed back feeling. Adding a resistor in between the PPS ECU (located to the left of the lower glove compartment, which needs to be removed if you want to add the resistor there) and the PPS solnoid located on the steering rack in the engine compartment. This results in the Power Steering adding less of a helping hand turning the wheels, hence giving a more weighted feel to the steering. I chose to create an extension to the harness, pluging it into the OEM harness in stead of cutting into the original harness. I don't like cutting in that and also the placement of the PPS ECU makes it very hard to work with.

Following parts are needed:

• Resistance, 50w, 8 ohm (I bought mine from RS-components for next to nothing)
  
• Regular 12V wire
  
• 90980-11002 & 90980-11003 from Toyota
  
• Pins to fit the two plugs from Toyota. (Get from an exisiting harness or Toyota garage as they cannot be bought from Toyota)
  
• Waterproofing material for wires (liquid gasket, glue, shrink insulation)
  

Tools:

[*] Soldering iron

[*] Soldering tin

First off, the plugs from Toyota comes without the pins in them, and apparently they cannot be purchased, so they need to be taken from an existing harness. If you don't have one lying around, pop by a Toyota garage and ask them to pick some from their inventory of old harnesses. They have the laying around for the same reason. It might be possible to find the pins from third party, but the Toyota ones are made to be water proof, so I would reccomend you go for those. Shouldn't cost more than a six pack or so..

When you have all compontents, it is simply to wire them up as I have done here:

Make sure to set the resistor is wired to the wire that will "continue" the limegreen-black striped wire on the original harness:

You can find the placement of the plug to the solnoid here (P1. This diagram is for a LHD, so the solnoid will be on the opposite side of the engine):

As the wiring diagram shows, the Lg-B (limegreen-black) wire (coming from ECU) will go to pin no. 1 in the plug you bought (that would be 90980-11003) and continue into the resistor and then to pin no 1 on 90980-11003 that again plugs into the harness that sits on the steering rack.

I would reccomend to use some shrink insulation and maybe some liquid gasket or glue to make sure all soldering is waterproof. There wont come much spray up there, but better safe than sorry.

When you have it all soldered and insulated, simply click in into the harness as described. When you add the 10" or so of extra wire you just created, make sure to fasten it somehow (I folded and fastened it to the existing harness). If not, it wire might be caught on the steering column, and you dont want that.

Go take a drive!

If any more questions, let me know and I will do my best to answer

Have you tried disconnecting the referenced plug and taking the car for a drive? Is there any difference between this mod and just removing the plug?

I'm sceptical as adding the resistor may simply be stopping the signal altogether and putting the steering into the same mode as removing the plug does.

If that's the case then it's a whole lot of work and hassle to end up with the same outcome as unplugging does.

I have, but it was quite a long time ago. It was VERY heavy in comparison. When up to speed, it might be usable (or not) but in slow city driving, it would be unusable.

The guy from the US forum, tried a 10 ohm resistor, which resulted in heavier steering than the 8 ohm. I have not tried 10, as 8 feels very good to me.

As another person indicated, it would be possible to ad a variable resistor and even have a dial somewhere to shift between weighting. I choose not to, to avoid further wiring laying around the car but I definately see the point of having very light steering when parking or so and very heavy when going on track. For now though, the 8 ohm works very very well for me.