I'm starting a new thread to discuss solutions to electrical problems that are inevitable when swapping engines into CANBUS vehicles like the RX8.

For those tackling engine swaps, an electrical understanding is a must. Any decent mechanic should be able to read a schematic but when it comes to signals not being what is required for their new engine, an electronics guru may be needed.

One thing I demand from my engine swap is that I maintain as many original electrical functions as I can including things like the cruise control and instrument cluster. This is where I'll keep a record of any solutions I've found.


Cruise Control:

The RX8 cruise control is handled by the ECU and drive-by-wire system. The buttons on the steering wheel only use one wire to signal the ECU which button is being pressed. Each button has a resistor connected to ground with the exception of the MAIN button which doesn't have a resistor. By applying a voltage to this wire (via a series resistor) it becomes a voltage divider. When a button is pressed is causes a voltage drop. Each button then produces a different voltage. For example... Say we use a 10k resistor to provide 12v to the cruise buttons. If the SET button was 10k, it would drop the voltage to 6v. If the DECEL button was 3k, it would drop the voltage to 2.77v. The MAIN button would equal 0v.

I'll post a schematic shortly showing exactly what's happening.


Cruise Control Solution:

The vehicle my engine came from had a different type of system. The buttons were located on the turn signal lever and each button had it's own electrical path to a dedicated cruise control module which drives a motor to pull a separate cable connected to the throttle body. I'm eliminating the drive-by-wire system so this type of cruise control works for me. This type of system is quite common in many vehicles and the solution I'm using could be applied to a number of vehicles.

I'll be using a microcontroller to detect the various voltage changes (off the RX8 cruise buttons) and convert it into individual outputs to drive the dedicated cruise module I'll be using. I'll need one analog input and 4 outputs for my application.


The Buttons:

Measured resistance when button is pushed:

None: infinity
Main: 0 ohm
Cancel: 120 ohm
Set: 680 ohm
Resume: 2.15k ohm


Using a 4.7K resistor as a supply I get:

None: 12v
Main: 0v
Cancel: 0.299v
Set: 1.517
Resume: 3.766v

From these values I can build a circuit to drive my cruise control module.


For Sale?

Since this method suits a wide range of cruise modules, I'd like a gauge any interest in purchasing the cruise converters. If there's interest I could have a small production of boards made. If not I'll just be protoboarding a single unit for my swap.

Schematic:

 

Cruise control option number 2:

The second option I'm looking into is locating another vehicle that also uses a "resistor-selective steering wheel mounted button assembly" (for lack of a better term) and simply swap out the resistors in my buttons to the values used in the donor cruise system. This may be easier -if- I can locate such a system that uses a separate cruise module.

Keep you posted...

EDIT - Looks like many of the 2000+ Nissan vehicles (Altima, Sentra) have a comparable cruise circuit that may function with the RX8 buttons. It's unlikely the resistor values are the same but swapping those and using a Nissan cruise control system may be the easiest solution. Here's the schematic of the steering wheel buttons. RX8 on top, Nissan on bottom. The other parts of the cruise circuit are pretty cut and dry. Brake and clutch signal, power, speed sensor input are all pretty simple on the Nissan unit.

The only complication I can see is the Nissan cruise has both terminals from the buttons going to the cruise module. The RX8 has one side grounded. It looks like the grounded side is on the colum side of the clock spring so maybe it can be seperated if need be.

 

I know it was a long time ago but would you share your schematic. I have the same setup in my swap and am capable of making a protoboard, just dont know electronics enough to figure it out.
Thanks

 

I'm pretty sure Nikola no longer participates in the forum.

 

He once mentioned he was also posting elsewhere. Anyone know where?

 

I found this one...

https://www.locostusa.com/forums/vie...=15737&start=0

Though it seems to have also gone dark in August, 2017. There's mention of an Isuzu forum in the last post (but no updates there since 2013). So guessing either the project was never completed or he finished it and decided to just leave everyone wondering how it turned out.

 

That project was a running joke for years before he left.

 

Just in case your interested, The Adaptronic Modular Series 1 Ecu retains all factory functions.