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00-04 Legacy ECM/ECU interchangeability


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My 00 Legacy GT has always been smooth as glass on and off throttle, but my 03 and 04 Outback/Legacy have always been like falling off a cliff when you get off of the gas. A high performance shop told me a few years back that it is due to emissions and cutting off the fuel in a less gradual manner on the later models.

 

My question is this. What controls that fuel delivery (ECU/ECM?) and will swapping in a part from a 00 work on a 03/04 to fix the fuel delivery problem.

 

It is worth noting that all are 5 speed manuals.

 

Thanks a bunch!

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Short answer, probably no.

 

the early cars 00-02 are all cable throttle bodies, i know i have an early 02 sometime mid/late 02 and depending on if the car is 50 state or cal emissions they switched to throttle bodies by wire.

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the parts catalog for the 04 shows that they are electronic throttle body cars, i would have to dig up the FSM's for 02, 03 and 04 to confirm what year made the switch for 50 states, iirc Cali cars made the switch a year before the rest of the cars to electronic throttle body.

 

if you wanted to swap ECU's you would need to know the FSM(wiring diagrams) for the car the ECU/ECM came off of and compare it to the FSM(wiring diagrams) for the car your putting it into and make sure they match for I/O if you want it be straight plug and play.

 

also, if you have a dirty iacv, or pcv, or a minor vaccum or emissions leak the car will feel like it has snap throttle.

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Thank you!

 

All of my 03/04 Legacies have had the problem. The performance shop looked at them and said that they fuel flow dropped off of a cliff without any throttle on. It certainly feels like it. Some have had iffy neutral sensors, and replacing those helped a bit, but none feel anything like the '00.

 

I wonder why all of mine look the same, cables on throttle bodies; no electronics.

 

s-l300.jpg

 

I think that I've look at the PCV and IACV before, but I'll double check my notes.

 

Some research reveals that the ECMs are not interchangeable, so i'll hunt a little for other things and then just continue to live with them. They're low mile cars (50k and 70k miles), so I'll likely have them forever.

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  • 1 month later...

A bit late to the party but even so, the biggest difference is the 00 5 speed has the EJ252 engine which has the late 90's style throttle body and intake manifold and o2 sensors and a Denso ECM to match.

 

By the time the 03/04 models came out they were all EJ251 with a newer style throttle body, intake manifold, and o2 sensors.

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Something that is completely unrelated to electronics, but lightweight flywheels reduce engine braking. So a closed throttle will do less driveline shock.

 

A tune up has always done me good too. Plugs, wires, coils, clean iacv, clean maf and or map, change fuel filter, stuff like that

Edited by RustyRuu
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  • 4 weeks later...
A bit late to the party but even so, the biggest difference is the 00 5 speed has the EJ252 engine which has the late 90's style throttle body and intake manifold and o2 sensors and a Denso ECM to match.

 

By the time the 03/04 models came out they were all EJ251 with a newer style throttle body, intake manifold, and o2 sensors.

 

 

I was about say, What? And then read the Wiki page for the EJ252: "The only notable differences confirmed are unique intake manifold and throttle body designs to accommodate the different MAP sensor location and IACV location.[14] They also have different cam and crank sprocket reluctor configuration."

 

Learn something new every day....but I'd still like to see a pic....and if it's got the Phase 2 heads, then the IM is more likely not compatible with either Phase 1 SOHC or DOHC heads/IM.

 

Still interesting to read that....I've heard/read about the 252, just thought is was the early PZEV or CA version.

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  • 1 month later...
I was about say, What? And then read the Wiki page for the EJ252: "The only notable differences confirmed are unique intake manifold and throttle body designs to accommodate the different MAP sensor location and IACV location.[14] They also have different cam and crank sprocket reluctor configuration."

 

Learn something new every day....but I'd still like to see a pic....and if it's got the Phase 2 heads, then the IM is more likely not compatible with either Phase 1 SOHC or DOHC heads/IM.

 

Still interesting to read that....I've heard/read about the 252, just thought is was the early PZEV or CA version.

 

I have a 2000 GT Limited with the 5 speed. It originally had the EJ252 engine. I wanted to do a Delicious Tuning ECM flash to try to get more power out of the engine and I ran into all sorts of issues.

 

The flash supports the EJ251 on the Unisia JEC ECM but the Legacy uses a Denso ECM that may or may not be flashable in the same way.

 

So I dropped my car off with my guy to do the head gaskets and pulled the ECM to send off for the flash. He had a Impreza ECM we thought would run the car and we swapped it in and the car wouldn't do anything.

 

That's what started my research into the EJ252 and my decision to convert the engine into a EJ251.

 

Subarus use two different driver's side cam sprockets with different marks on the back for the sensor and they are different enough that if you have the wrong set the motor won't start.

 

The 90's EJ engines used a narrow band 4 wire AF sensor ahead of the CAT and a Map / MAF (I can't remember which) in the intake with a simpler throttle body. The EJ251 introduced a new throttle body with an outbound atmospheric sensor and a combined air temp / volume sensor on the intake. It also added an air assist throttle control and a wide band 6 wire front AF sensor.

 

So my build became Delta 1500 cams, heads ported and polished, lightweight crank pulley, Stage 1 flash and Cobb EL headers and a Cobb Hi Flow Cat.

 

That was the plan. All these other bits were needed to support the flash. I sourced another JEC ECM for the flash, Cam Sprockets with the other marks, a full intake manifold and throttlebody from a EJ251, a huge chunk of a body to engine harness from an automatic Outback that I broke apart to add more wires to my existing harness to support the different sensors, a complete EJ251 engine harness to go with the EJ251 intake, the outboard atmospheric sensor and harness, new wideband AF sensor and new O2 sensor (post Cat).

 

There are a few wires that need to move in the connectors to the ECM. I spent a lot of time looking at the wiring diagrams for the automatic and manual Legacy's and the Forester model that my replacement ECM came from.

 

The EJ252 was a transition engine that only appeared in the Legacy 5 speed 00-02 or so. It used parts from a bunch of other engines, some older some newer. The emissions were from the 90's while the crank sprocket shows up in later cars. The block and heads are the same as the EJ251 so all those parts are the same, not dual cam EJ25 or older EJ22 from the previous generation Legacy.

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That is really interesting. Thank you (saving it to my personal file!).

 

I wish that all three of mine had the engine in my 2000 GT manual. It is so much smoother.

Edited by bmart
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