In this blog post we discuss the issues with swapping a Single AVCS CANbus (shortened to CAN for the rest of this blog) equipped engines like a 2008 WRX into an older non-CAN equipped chassis like a 2002 WRX.
When doing a swap with a CAN equipped single AVCS engine, the biggest issue will be dealing with the CAN system (read more about that here and part 2 here). After working through this a couple of different ways we have determined the best way to do this is by swapping out the CAN equipped ECU with an equivalent NON CAN ECU. More details about how and why below.
Which models come with Single AVCS engines and are CAN equipped?
2005+ Legacy GT
2008-2014 Forester XT
What do I need to do if I want to swap this engine into an older non-CAN chassis?
Let's take a scenario with a 2008 WRX engine that is going into a 2002 WRX. There are three options. First is that a standalone ECU could be utilized either with a model that offers a plug and play for the turbo ECU (IE Haltech has a 2008 WRX jumper harness for their Elite ECUs) or custom fabricate a harness from the standalone out to the engine and merge that in. The second option could be utilizing a CAN Emulator. We have done this a few times but for now, have found the process cumbersome due to the immobilizer circuit running through the gauge cluster. The third and best option is to move away from the CAN ECU and switch to one with the same capabilities to run the engine without the CAN related issues.
If you have a 2008-2014 WRX, 2009-2014 Forester XT, or 2008-2012 Legacy GT/Outback XT engine
We'll run these models on a 2007 WRX ECU with a 2008-2010 WRX harness so that the wiring at the ECU matches the non CAN equipped 2007 WRX ECU and engine plug matches the newer engine. 2007 WRX models have all of the secondary air pump wiring and emissions equipment the 08+ model does, so this could pass smog without a reflash.
If you have a 2005-2006 Legacy GT or Outback XT Engine
These models are the only models that came with CAN equipped ECUs but do not have the secondary air injection system which makes it a little more complicated. We would run these engines with the same 2007 WRX ECU, however, it would be paired with a 2007 WRX harness unlike the above example due to the layout of the engine plugs. If smog is not a concern this would allow the 2005/2006 GT/XT intake manifold and harness to stay.
If you live in a state like California where you can't reflash the ECU to pass smog, the 2007 WRX ECU would not be a good option. The better route for these applications is to swap the intake manifold and harness to either a 2004-2006 STi intake or 2004-2005 Forester XT harness because they are Single AVCS models with drive by wire but do not have the secondary air injection system. We'll then wire up your swap with matching XT or STi ECU and harness.
What about dual AVCS engines like a 2008 + STi?
Unfortunately at this time there aren't any great options because there aren't any NON CAN OEM ECUs that have the ability to run exhaust AVCS. Most of the time we would wire this to a standalone ECU like a Haltech Elite 2500 that has the ability to utilize the exhaust side AVCS. If smog is a concern we would wire it up like the 2008+ single AVCS models with a 2007 WRX ECU and ignore the exhaust AVCS.
2 wire to 3 wire Coolant Temperature Sensor
For all the above scenarios, a conversion will need to happen with the coolant temp sensor from the 2 wire model found on CAN equipped cars to the 3 wire version that comes with the non CAN models. This change is because the 2 wire sends the temperature signal direct to the ECU and then the ECU transmits that information to the cluster via the CAN system. On non CAN equipped models there are 2 separate wires for the coolant temperature signal. One to the ECU and one to the cluster directly from the sensor.
*All credit goes to iWire Subaru Wiring Service
Article Source: https://www.iwireservices.com/post/single-avcs-canbus-equipped-engine-swap