NSX EPS Unit Upgrade

[NSX78__]

Hey guys, been reading on our cars eps unit system and found that there are NSX owners in Japan that convert their old early separated EPS control unit and power unit to the integrated NA2 unit that uses only torque sensor (39980-SL0-053) with a custom made harness. I'm very interested to do this upgrade but I'm just left with a few thoughts that I would like the NSX experts to fill in.

1.Problem is mine is a 93 auto that uses the gearbox AT control unit. I have read in a Japanese blog that the gearbox AT control unit exchanges signals to the EPS control/power unit for the EPS to function.
2. I do know the NA2 EPS system removed the rotational sensor and its only torque sensor driven but this upgrade works on the NA1 racks with as well.
3. My concern is since the new EPS unit does not have the rotational sensor, will it malfunction with the gearbox AT control unit since its missing the rotational sensor or the gearbox AT control unit only sends signals from the VSS to the EPS system? Am I thinking too much? Logically it doesn't make sense that the rotational sensor would have anything to do with the gearbox brain but 90s electronics are weird sometimes hmmm.

I really want to keep the EPS and if there's anyone wondering why did i not opt for the 95 eps unit that still runs both torque and rotational sensor is cause I plan to run the new EPS steering rack that only uses the torque sensor in the future as the 95 eps steering rack that uses both torque and rotational is no longer available to purchase. TIA

 

[Old Guy]

First off, not an EPS expert, in particular because I have not had the need to fiddle with the EPS on my 2000. All of this is inferred from parsing the wiring diagrams in the service manuals.

I don't think the TCM 'exchanges' data with the EPS controller. The TCM passes a countershaft speed signal to the EPS unit and that function exists on 97+ NSXs automatic transmission TCMs. On 97+ cars which do not have an auto there is a separate module called a pulse unit which combined with a differential speed sensor performs that function. Since you have an auto you already have that countershaft speed signal from the TCM which the later EPS needs. The only issues would be are the countershaft speed to pulse rates the same and are the voltage levels compatible. As far as I can tell the part number for the EPS controller on the 97+ cars is not transmission dependent implying a unidirectional data path. As such, I expect that the TCM - EPS data connection is uni directional. It is really hard to conceive of a universe in which the TCM needs to know the rotational speed of the steering wheel to function.

In addition to the torque sensor signals, the 97+ EPS torque sensor passes a +2.5 volt voltage reference signal back to the EPS unit. It looks like this also exists in the 1991 torque sensor interface and it is called out as 2.5 volts in the 1992 ETS manual; but, depending on whether you look at the 1991 service manual or the 1992 ETS there are pin assignment discrepancies. The 1991 service manual does have some errors so I don't know whether this an error or reflects a product change. Just something to be aware of when confirming the pin assignments in your conversion harness.

I am curious about why you want to do this. Unlike the 2000+ ABS system replacement it is not obvious that the controller alone would necessarily be an upgrade. If your controller has failed then fitting the later controller would be one alternative for a repair if it is determined that the controller / amplifier is not amenable to the usual repairs. It would be consistent with a plan to ultimately install the later steering rack. However, if your current controller works and the plan is a complete switch to the later EPS system then I would be inclined to skip the purchase of the custom harness and just install the later controller and rack as a matched set at that later date. If you just do the controller conversion now you may find at a later date that 97+ EPS racks are no longer available in which case you are stuck with an un-matched system.