JEC ECU swap for 00 Legacy GT

[Regardie]

So I am looking for a little help and to see if anybody has done something like this before.

I have a 2000 Legacy GT 5MT EJ252 with 186K miles and I need to do the head gaskets. So while the engine is out of the car, I am sending the cams off to Delta to get a 1500 grind. I wanted to send the ECU off to Delicious Tuning for a Stage 1 map / reflash but that only works with the JEC ECUs from the Impreza / Forester, not the US made Denso ECU that is in the Legacy.

I have done a fair amount of research and I have sourced a JEC ECU from a 00 Forester for the reflash. Both cars run the EJ251/2 with MAP. Both ECUs have a 3 connector set that are largely similar in pinouts (from the OBD-II section of the FSM).

The problems that I am anticipating:

The Cam and Crank Sprockets. Subaru used two styles of cam and crank sprockets that must be changed in sets or the engine won't even turn over. I believe the Legacy has one style and the Forester / RS has the other style. The gears are fairly cheap and since the timing components are being replaced, I am getting new gears.

The front O2 sensor. My car has a 4 pin O2 sensor that only returns one signal. The Forester ECU wants to see four signals from a 6 pin O2 sensor. I'm not sure how I will get around that. The auto 00 Legacy has the same setup as the Forester.

The IACV (Idle Air Control Solenoid Valve) - mine is 3 pin / one signal, others 6 pin / 4 signals. Once again the auto is the same. Not sure how I am going to get around this either.

There are a couple wires that need to move as well. Rear defogger and small light switch show up in different places.

Has anyone tried this to get some more power out of the 3rd gen Legacy?

[r3v_v3ng3]

You have the California version (3 pin IACV/4 pin front O2 sensor) the cam/crank gear is also different. You can try to source up a 99 impreza 2.2 ECU that came in CA version, maybe its made by JEC.

The only other way would be to source up a Legacy parts car that is the same year as yours and get the bulkhead wiring harness, engine harness, cam/crank gear, O2 sensors, IACV (maybe more). Make sure its not the CA version

[Regardie]

Strange, I never thought about Ca spec versus US spec. The 2000 FSM has two wiring diagrams, MT and AT, along with two diagrams of pinouts of the ECU. My car matches the MT diagrams. My car is MAP while those earlier cars are MAF based so their ECUs won't work either. The Forester and RS in my year used the same parts for both MT and AT. It seems that the EJ252 is the outlier in the Legacy 5MT for 00-01.

So yes it looks like a harness merge is in my future if I want to continue this project.

[Regardie]

My builder and I have finished this swap. The main issue was the EJ252 that only came in the Legacy 5MT for 00-02. The EJ252 uses a combination of old and new parts that are not used together anywhere else in the EJ line. It has the old style IACV, front A/F sensor, throttle body, intake manifold, pressure sensor, but new style cam and crank gears.

The EJ251 has the newer intake manifold and throttle body, different IACV, an Air Assist solenoid valve, and outbound atmospheric pressure sensor. It is set up to use a wideband A/F sensor.

The process is surprisingly easy once you understand what the issues are to complete the swap. I sourced a 2000 Legacy 4EAT engine harness, and a replacement set of cam and crank gears. I got a huge chunk of a 2000 Legacy Outback 4EAT body harness, including the bit to the passenger strut tower atmospheric pressure sensor, and the sensor itself, and the bit down to the front A/F sensor. I pulled that harness apart and lifted just the 6 or so wires that I needed from it.

We tried to use my intake manifold with parts off a Forester manifold that my guy had laying about but the casting was too different so an EJ251 intake and throttle body are required to do this swap. We used the one he had at the shop and now he has mine.

A few wires needed to be pulled through the firewall and added to the existing harness and a few pins needed to be moved around on the existing harness to make them line up with the new ECM.

The end result is I now have a 2000 Legacy GT 5MT with an EJ251 and a Forester ECM with a Delicious Tuning Stage 1 flash. The car seems like it has a little extra go and I hope to get it on a dyno at some point to give us some hard numbers. These are the things that should have increased the HP and torque: moving to the 251 adds a little according to Subaru specs, the lightweight crank pulley, the Delta 1500 cams, the port and polish of the heads, the Grimmspeed manifold spacer, and the Stage 1 flash.

In the future I expect some EL headers, and an upgraded high flow cat, and axle back, probably 2.5 inch.

Then the 5MT will need to go since my replacement is showing it's age so I guess a 6MT could be in my future.