Power Steering Conversion Help

[GTLabAustin]

Hey there everyone, thanks in advance for any help provided here.

I'm currently converting my 91 manual NSX over to EPS, but have hit a bit of a snag. What I really need some assistance with is identifying the wires coming out of the rack itself. I've looked at all of the available schematics, but I cant find anything that matches up with the wire colors that go from the motors and sensors within the power steering rack to the first set of connectors. This has left my conversion in limbo and I really want to get it done if possible!

There are 9 wires coming from the rack itself (10 if you count the ground strap, but i can figure that one out

Here's the breakdown

The first connector has three wires in total (I believe these are for the rotation sensor??)
-Yellow
-White
-Whit / Blk

The second connector has six wires (I believe these are for the torque sensor?)
-Yellow/blk
-Yellow/Grn
-White/Grn
-White/Red
-Orange
-Blue

Again, any help here would be soo greatly appreciated. It seems like all the schematics reference color wires that lie between the eps controller and wiring harness rather than between this harness and the rack itself.

Hope that makes sense. I'll be happy to provide any additional details/clarification/pictures if needed.

 

[Old Guy]

If you are retrofitting an early EPS unit to your car, page 17-40 of the 1991 service manual provides a schematic with wire colors for the connections from the controller and the power unit to the rack. Unfortunately, it does not provide the pin designations for the connectors on the rack or the power unit; but, from the internal schematic of the power unit you should be able to figure out what is going where. Also, on page 19 of the schematics at the very end of the electrical section of the service manual there is a similar breakdown of the wiring.

However, none of your wire descriptions jive with the 1991 service manual. Are you retrofitting an EPS from a later car - one with the integrated controller and power unit? If so, do you have the model year for your rack and controller?

 

[JohnWayne]

Do you already have the rack and EPS computer?

 

[GTLabAustin]

If you are retrofitting an early EPS unit to your car, page 17-40 of the 1991 service manual provides a schematic with wire colors for the connections from the controller and the power unit to the rack. Unfortunately, it does not provide the pin designations for the connectors on the rack or the power unit; but, from the internal schematic of the power unit you should be able to figure out what is going where. Also, on page 19 of the schematics at the very end of the electrical section of the service manual there is a similar breakdown of the wiring.

However, none of your wire descriptions jive with the 1991 service manual. Are you retrofitting an EPS from a later car - one with the integrated controller and power unit? If so, do you have the model year for your rack and controller?

Thank you for taking the time to look at the service manual, I really appreciate it. I have been reviewing page 17-40 along with the electrical schematics you mentioned at the end of the manual. They have been very helpful, but I'm still down to identifying these wires coming from the rack.

Here's some further details:

The rack I have is from a 1991 NSX auto (PN 53180-SLO)

The controller is a later model with integrated power unit (PN 39980-SLO-053)

I know that these two specific components weren't used from the factory together, but after reviewing the schematics and various inputs/outputs, there doesn't seem to be any reason why they can't be. Once I identify the correct sensor wires from the rack, I should be able to test the system.

I've already installed the components and built a custom wiring harness. Everything is connected other than these 9 wires, so really hoping to get it sorted out!

 

[GTLabAustin]

If you are retrofitting an early EPS unit to your car, page 17-40 of the 1991 service manual provides a schematic with wire colors for the connections from the controller and the power unit to the rack. Unfortunately, it does not provide the pin designations for the connectors on the rack or the power unit; but, from the internal schematic of the power unit you should be able to figure out what is going where. Also, on page 19 of the schematics at the very end of the electrical section of the service manual there is a similar breakdown of the wiring.

However, none of your wire descriptions jive with the 1991 service manual. Are you retrofitting an EPS from a later car - one with the integrated controller and power unit? If so, do you have the model year for your rack and controller?

Thanks for taking the time to look into it! I've reviewed the pages you referenced and haven't been able to figure it out. Do you have any idea where I could locate an internal schematic for the power unit? I have not been able to find one.

Here's a few more details on the parts I'm working with.

The rack is from a 92 automatic (PN 53180-SLO)

The controller is a later model with the integrated power supply (PN 39980-SLO-053)

I know that these parts weren't used together from the factory, but I looked at the pinout for the ECU closely and have built a custom harness so that it can all talk to one another. The parts are already in the car and installed save for these last remaining wires.

If anyone has the internal schematic for the power rack (showing which wire represents TRQ1, TRQ2, ROT1 etc), that would get me going.

Alternatively, if anyone has a 91 auto and would be willing to take a look at your EPS rack harness and tell me if the wires change color at these connectors (and how the match up), I would be willing to pay your for your time and effort.

Thanks again!

 

[GTLabAustin]

test

 

[GTLabAustin]

Sorry, I tried to reply to this days ago, but my posts did not show up. Not sure why, but seems to be working now.

Old Guy - Thanks for taking the time to look into this! I have also reviewed the pages you referenced in the shop manual, and have not been able to answer my question. Do you happen to have the internal schematic for the power unit? I have not been able to locate one.

Here's the details on my rack and controller

Rack is from a 1992 auto - PN 53180-SLO

Controller is a later model with integrated power unit - PN 39980-SLO-053

I know that typically these two weren't used together from the factory, but I did a little research and reviewed the pinnout from the ECU before moving forward. I don't see any reason why they couldn't be used together (provided I know which wires from the rack correspond to TRQ1, TRQ2, ROT1, etc). I've already built the custom wiring harness and have everything hooked up save for the 9 wires I mentioned.

Thanks again!

 

[Old Guy]

On the rack used on the later cars, the wire colors and functions coming out of the steering sensor on the rack are as follows. Note that there is a wire color transition between the internal sensor on the rack and the wires that go into the 18 pin connector on the EPS control unit on later cars.

Internal wiring
6 pin connector _____18 pin connector on control unit
yel/blk - Vref _________grn/red pin 13
wht/grn - TRQ1 _______lt grn/yel pin 11
yel/grn - TRQ3 ________grn/yel pin 10
wht/red - TRQ2 _______blu/blk pin 3
orn - SPS (power) _____lt grn/blk pin 2
blu - grnd ____________blk/yel pin 17
(The message editor appears to suppress blank spaces so I had to enter under score to separate the above table columns)

Looking at the crude schematic for the 1991 rack torque sensor the function designations are as follows

Grn/red - Vref
lt grn/yel - VT1
grn/yel - VT3
blu/blk - VT2
lt grn/blk - SPS (power)
blk/yel pin - grnd

So, it looks like the torque sensor control wiring on early and late racks matches up, assuming VT1 is equivalent to TRQ1, VT2 =TRQ2 and VT3= TRQ3. The later control units (and racks) do not use a steering rotation sensor. The torque sensor signal voltages for the 1991 cars (pg 17-52 of 1991 manual) appear to be consistent with the torque sensor signal voltages for the 1997 and later cars (pg 17-34 of the 1997 service manual).

Free .pdf copies of the 1991 and 1997 service manuals are available on-line. I suggest you get them and compare to make sure I did not mess up the color assignments on the wiring.
​

 

[GTLabAustin]

This is sooo helpful! Thank you

 

[GTLabAustin]

Old Guy - Could you tell me where you were able to find a schematic for the rack wiring harness? I looked at the manuals again and couldn't find where you located the "Internal Wiring for 6-pin connector"

I have only three wires left to identify and connect before testing. The wires come from the rack and have the following colors - (white), (yellow), and (white/black). I suspect that these wires correspond to ROT1 (#4 on 18 pin connector), PHC (#8 on 18 pin connector), and ROT2 (#12 on 18 pin connector). I'm just not sure exactly how they match up and don't want to start plugging things in without identifying them first.

Thanks again. You've really been a huge help

 

[Old Guy]

The crude schematic (actually more of a functional block diagram) for the 1991 rack is on page 17-40 of the 1991 service manual. Unfortunately, it shows the wire colors on harness on the outside of the rack; but, does not show the colors on the inside of the rack. There is a transition at the plug. Page 17-18 of the 1997 service manual shows roughly the same functional diagram for the 1997 rack which shows the wire colors on the inside of the rack and the rack - control unit harness. The 'inside' wire colors match up with the wire colors for the 6 pin connector you listed in your first post.

You list wires in positions #4 , #8 and #12 on the 18 pin connector. On pg 17-19 of the 1997 service manual you will see that on the 1997 cars (and up to at least 2003) those 3 pins are unpopulated on the 18 pin connector. On the 1991 service manual you will see that #4 , #8 and #12 on the 18 pin connector appear to be populated; but, not with the wire colors you listed and I don't recognize those wire functions.

Your controller SL0 (zero not Oh) is the 1997-2003 EPS controller so it should match up with the connector configuration on pg 17-19 of the 1997 service manual. Are you looking at the 18 pin connector for the 1991 EPS or the 1997+ EPS where you see #4 , #8 and #12 populated? Perhaps you have mirror imaged your pin numbering? However, you 3 wire colors don't really jive with anything on the service manual diagrams.

 

[GTLabAustin]

We must be looking at different manuals(?), because 17-19 in my 1997 manual shows removal and installation of the steering gearbox.

Here's is what I've been referencing for the 18 pin connector on my EPS controller (below).

The wires I mentioned above that I'm trying to identify (white, yellow, white/black) come out of the rack itself and then into a four-pin connector (with one blank position). As we've already determined, the wires coming from the rack are not consistent on either side of the 6 (and this 4 pin) connector. You were able to match up either side of the 6-pin connector above, I'm just stuck on these remaining 3

 

[Old Guy]

On the very first page of your service manual at the bottom left there is an edition number. Mine is First Edition 1/97 1476 pages . The part number on the back cover at the very bottom is 61SL006. If your part number is 61SL004 you have the 1995 edition. 61SL005 is the 1996 shop manual supplement (a complete service manual was not released in 1996). Also, is it a North American service manual?


That pin assignment diagram looks like a pre 1997 service manual because Honda ditched the rotation sensor on the later EPS controllers. I have the same assignment chart as you show above; but, it is on page 17-20 of my 1997 service manual.​

 

[GTLabAustin]

Ahh, you're absolutely right. I was referencing the pre 97 schematic. Thanks again for pointing me in the right direction. I will look for the correct version and modify my harness accordingly. Hopefully I can get this done and document the details for anyone that's motivated to do something similar.

 

[GTLabAustin]

Just to confirm 100%, when the schematic says "Wire side of Female Terminals", this references the view when looking at the wiring harness, correct?

For example, If I'm looking at the EPS controller, position "1" as shown on the schematic would be in the upper right position, correct?

 

[Old Guy]

Just to confirm 100%, when the schematic says "Wire side of Female Terminals", this references the view when looking at the wiring harness, correct?

For example, If I'm looking at the EPS controller, position "1" as shown on the schematic would be in the upper right position, correct?

The side of the plug pair that has the little exposed metal contacts is the male terminal. The other side that receives the metal contacts is the female terminal. Typically, the male side of the pair of terminals would be on the controller box and the female side would be the wire harness side. I have not removed my EPS to be 100% sure; but, that is the norm for any other piece that I have maintained.

When they say "Wire side of Female Terminals" that would mean that you are looking at the back side of the female plug where the wires enter the plug body. I wouldn't use the term upper since 'up' on the diagram may not necessarily be up when installed if you are referring to the controller Always reference it to the locating keyway on the plug body viewed from the wire side of the plug body.

​

 

[drew]

The first few pages of the ETM and the wiring diagram section of the shop manual go over the nomenclature and standards. They are very clear about it, with pics and the diagrams do indicate gender.

 

[GTLabAustin]

Thank you. I actually found that just after asking. Spent a little time working on it again yesterday and will likely test the system later today.

 

[Birki_Black_91NSX]

Hey [MENTION=36891]GTLabAustin[/MENTION] how did you go with the conversion? I own a 91 manual NSX and also want to do the conversion. Whats involved from mechanical side of it? ..... I can see the wiring side is a challenge


Sent from my SM-N975F using Tapatalk