fb25 swap from ej25 on 2010-2012 legacy

so i have an issue with a fourth gen naturally aspirated legacy but have a question that is pertinent to the fifth generation legacies

 

i am wondering if the ej25 ecu from fifth gen for years 2010-2012 is compatible with the fb25 ecu for the years 2013-2014. granted it is going to run, i have the intention to run logs and tune it with the romraider software and a tactrix cable, but the primary question is if the earlier ecu can run the fb25 motour

 

another question is how the different transmissions (cvt from 13-14 versus 4EAT from 10-12) will impact things

 

background info:

in model years 2010-2012 the (fifth generation legacy with ej25) moved to ignition coils from plug wires and distributor cap; so this is the first question, is the ecu from fourth gen still plug and play here even with the early fifth generation model years where the motor is still an EJ25 SOHC. In 2013-2014 model years it moved to twin cams and a timing chain and significant hardware internal hardware changes with the FB25 motor, but the harness seems mostly the same with the ej25 motor from earlier fifth gen legacy, but it is unclear if ecu would be blind to these changes. it seems the harness connections all connect inside the engine bay and into the original ecu the same way

 

 

 

appreciate any input omg thanks

As with most cars nowadays the ecu isn't blind to anything at all. The canbus system is very unforgiving in these cars. I don't believe a sohc ecm will run a dohc motor in any subaru without eliminating the extra sensor somehow.

 

As far as tuning the different model years, XRT tuning does all of them maybe you could join his FB group and ask him direct he is very knowledgeable and helps wherever possible. I don't think I would waste my time with different years of ecms just for the sake of tuning, considering it can and has been done on the fb engine already.

As with most cars nowadays the ecu isn't blind to anything at all. The canbus system is very unforgiving in these cars. I don't believe a sohc ecm will run a dohc motor in any subaru without eliminating the extra sensor somehow.

 

thanks for your input!

 

just a thought, but wouldn't elimintaing that sensor amount to not plugging it in; if the original sohc ecu and harness are retained, there wouldn't be a connector to plug it into, so the ecu would run as if sohc, so if it were to run, wouldnt the distinction sohc vs dohc be transparent to the ecu?

 

after all the point of the sensor is to tell you when the sensor actually fails or the engine has blown, or no?

 

omg thanks

thanks for your input!

 

just a thought, but wouldn't elimintaing that sensor amount to not plugging it in; if the original sohc ecu and harness are retained, there wouldn't be a connector to plug it into, so the ecu would run as if sohc, so if it were to run, wouldnt the distinction sohc vs dohc be transparent to the ecu?

 

after all the point of the sensor is to tell you when the sensor actually fails or the engine has blown, or no?

 

omg thanks

 

The ecm uses the cam and crank sensors to determine mechanical timing and to set programmable timing. My understanding is the two engines (sohc and dohc) use the sensors differently. Also the FB motor uses dual avcs which cannot be controlled by the sohc ecu. This is why the engine has multiple cam sensors and also oil control solenoids.

 

Now, say you do get the ecm to run the engine using a single cam sensor input, now you have crippled all the advanced hardware on the engine and taken your power output all the way back to like 1996.

 

There is almost no case in which this would make any sense to do, unless you happen to have an FB engine laying around free to you, and you absolutely needed it to work in your sohc car. But even then the fb25 would be worth more to someone looking for one than a sohc ej25 would cost in a salvage yard.

thanks so much for this; literally answers everything. this is my thread in the fourth-gen section where ppl are slightly less clueless than i, but you are clearly way less clueless omg thanks

So you want to put all this into a 4th gen...a swap worth doing would be the fa20 in the newer wrx, make sure the front crossmember is compatible since they do have an upgraded chassis. The 5th gen legacy/outback uses a funky engine mount system not used in any other Subaru.

 

There is probably a standalone system that would run everything as well. For the time you would be putting into the swap it would be worth having a ready to go solution for the ecm. Those engines also have dual avcs, but Idk how you would get the DI to work properly.

several aftermarket ecu companies make subaru specific ecu. or you could swap the full harness from the fa car into the 4th gen.

...5th gen legacy/outback uses a funky engine mount system not used in any other Subaru

 

i noticed; but at least fb20 engine mounts look similar to the ej sohc mounts

 

a ready to go solution for the ecm. Those engines also have dual avcs, but Idk how you would get the DI to work properly.

 

i meant the fb20, not fa20; i would swap over the fb20 ecu, tcu, and wiring as the complete drivetrain with minimal disassembly as complete

and then drop-in; these aren't di, but if i did the same swap with fa20, i don't see why the di would be a problem, or would it

 

do you know if my fourth-gen rear differential would be compatible?

 

omg thanx

Edited October 1, 2020 by darthqwo

i noticed; but at least fb20 engine mounts look similar to the ej sohc mounts

 

 

 

i meant the fb20, not fa20; i would swap over the fb20 ecu, tcu, and wiring as the complete drivetrain with minimal disassembly as complete

and then drop-in; these aren't di, but if i did the same swap with fa20, i don't see why the di would be a problem, or would it

 

do you know if my fourth-gen rear differential would be compatible?

 

omg thanx

I think you would have a better chance at getting an fa20/6mt to work than the fb25 and cvt. I dont think thats gonna work in the 4th gen at all. You would need to swap the entire wiring harness for the whole car, I don't think you understand exactly how unheard of this would be. You need everything swapped over, dash, hvac, seat wiring, body wiring...etc...

 

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I think you would have a better chance at getting an fa20/6mt to work than the fb25 and cvt.

 

so, in that case im still wondering about my rear differnetial; is gear ratio going to require a swap here as well; if anyone knows about this so, a rear differential swap is a possible compatibility issue; but fifth gen legacy has both a 5eat and cvt; and fourth gen legacies also have a 5eat, so the latter might accommodate the cvt as well if they bolt up the same way (this is a common logic in the forum for cross compatibility between model years and generations)

 

 

I dont think thats gonna work in the 4th gen at all. You would need to swap the entire wiring harness for the whole car, I don't think you understand exactly how unheard of this would be. You need everything swapped over, dash, hvac, seat wiring, body wiring...etc...

 

the only other items would be the biu (immobilizer), instrument cluster, and key; the steering wheel has shifters, so if i require that i would have to look into, but hvac, seats, body, airbag, etc., bear no relevance to the swap unless i am mistaken. i've taken the dash out before in the junkyard on my model year; it is easy once you have done it, but it is not necessary to get to the cluster

Edited October 2, 2020 by darthqwo

so, in that case im still wondering about my rear differnetial; is gear ratio going to require a swap here as well; if anyone knows about this so, a rear differential swap is a possible compatibility issue; but fifth gen legacy has both a 5eat and cvt; and fourth gen legacies also have a 5eat, so the latter might accommodate the cvt as well if they bolt up the same way (this is a common logic in the forum for cross compatibility between model years and generations)

 

 

 

 

the only other items would be the biu (immobilizer), instrument cluster, and key; the steering wheel has shifters, so if i require that i would have to look into, but hvac, seats, body, airbag, etc., bear no relevance to the swap unless i am mistaken. i've taken the dash out before in the junkyard on my model year; it is easy once you have done it, but it is not necessary to get to the cluster

You need to do more reading on canbus systems. For it to work properly you need everything, and I mean everything from the car to swap into yours. Everything in these cars is connected to the canbus network, the seats, doors, dash...everything. Unless you are finding an aftermarket controller to run the cvt, you need the entire car harness complete, because its all connected, especially the dash and cluster. And the rear-end is the least of your problems, they all fit the same way so you would need to swap that as well, the 5eat is geared differently than the cvt.

 

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finding a cvt used that hasn't failed may be an issue. the reason the cars sell cheap is the cvt is very expensive to repair as it has no user serviceable parts

finding a cvt used that hasn't failed may be an issue. the reason the cars sell cheap is the cvt is very expensive to repair as it has no user serviceable parts

 

Yup. That's probably the biggest reason why I sold mine.

for completeness

 

so, a little belated detail for completeness

 

the foresters between 2011-2013 are all fb25 engine with 4EAT transmissions lol; moreover, crossmember (engine cradle) compatibility is retained between engine generations on the forester backwards through 2009 and is the same on the imprezas turbo and nonturbo from 2008-2014, according to part numbers. #this is a no-go for the 2010-2012 legacies/outbax where the oil pan would hit the crossmember at the upper and lower pan rears; these aren't fb25s but they are ej25s with an oil pan unique to the fifth gen to accommdoate the garret turbo from the fa20

 

the reason this is significant is any other model and year with the fb25 automatics will have a cvt and require a complete drivetrain swap complete with dash harness and tcu; also it wasn't clear from the other models and years about crossmember compatiblity. so one could just drop in an fb25 motor, and all you need is an ecu from a forester from these model years to complete the swap while retaining your 4eat; i checked the tcu for these model years, and it appears to look identical, so a dash harness swap would be also unnecessary unlike the cvt models (i.e., imprezas, legacies). so for anyone wanting to make a swap this is the way to go. #also need forester biu, instrument cluster, and key--or otherwise bypass immobiliser

Ok so I'm really lost right know and am in need of someone to guide me in the right direction please!! So I bought a 2011 forester with a fb 25 motor had it for a month engine crapped out on me cause it threw a rod I'm limited on funds so I couldn't get the same motor so I found a 2011 subaru legacy with a ej 25 sohc so I grabbed it threw it in and all it does is crank and the harness that it came with is the one I used so the main plugs only the gray one is plugged in it didn't have the brown one is that my problem? It's my family's only mode of transportation so I got it all done in 2 days and never done a subaru motor and really don't no to much about them if there's any guidance someone can give I would greatly appreciate it

Ok so I'm really lost right know and am in need of someone to guide me in the right direction please!! So I bought a 2011 forester with a fb 25 motor had it for a month engine crapped out on me cause it threw a rod I'm limited on funds so I couldn't get the same motor so I found a 2011 subaru legacy with a ej 25 sohc so I grabbed it threw it in and all it does is crank and the harness that it came with is the one I used so the main plugs only the gray one is plugged in it didn't have the brown one is that my problem? It's my family's only mode of transportation so I got it all done in 2 days and never done a subaru motor and really don't no to much about them if there's any guidance someone can give I would greatly appreciate it

 

Did you even bothet reading this thread? You can't just swap from a fb25 to ej25 and expect it to work. I know it sucks to hear, but you wasted your time and money.

Ok so I'm really lost right know and am in need of someone to guide me in the right direction please!! So I bought a 2011 forester with a fb 25 motor had it for a month engine crapped out on me cause it threw a rod I'm limited on funds so I couldn't get the same motor so I found a 2011 subaru legacy with a ej 25 sohc so I grabbed it threw it in and all it does is crank and the harness that it came with is the one I used so the main plugs only the gray one is plugged in it didn't have the brown one is that my problem? It's my family's only mode of transportation so I got it all done in 2 days and never done a subaru motor and really don't no to much about them if there's any guidance someone can give I would greatly appreciate it

 

 

You can send both harness to a pro to be merged. That would be a step one worthy of a used engine financially.

 

Step two would probably be an open source tune to get things to talk. Still probably the same price as a used engine .

 

The road ahead is probably as or more expensive than the one you’ve started down already

 

 

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Swapping an ej25 into an FB platform isn't even worth the time and effort just get the correct engine.

finding a cvt used that hasn't failed may be an issue. the reason the cars sell cheap is the cvt is very expensive to repair as it has no user serviceable parts

 

Wait I am not sure about these things failing. The place that built my 06 LGT did the work on my 2013 CVT legacy. They have yet to see one fail with the steal belt cvt. they said as long as the are serviced right then you will have not problem. I had my 2013 done and the car runs very good now at 124K miles.

Swapping an ej25 into an FB platform isn't even worth the time and effort just get the correct engine.

 

hahaah this reminds me of people doing ej20X swaps and they never work right.

Ok so I'm really lost right know and am in need of someone to guide me in the right direction please!! So I bought a 2011 forester with a fb 25 motor had it for a month engine crapped out on me cause it threw a rod I'm limited on funds so I couldn't get the same motor so I found a 2011 subaru legacy with a ej 25 sohc so I grabbed it threw it in and all it does is crank and the harness that it came with is the one I used so the main plugs only the gray one is plugged in it didn't have the brown one is that my problem? It's my family's only mode of transportation so I got it all done in 2 days and never done a subaru motor and really don't no to much about them if there's any guidance someone can give I would greatly appreciate it

 

They may look similar but FB and EJ are different motors. Different, size bore, stroke, timing chain vs Timing belt. Your best bet is get a FB25 and sell the EJ25. One issue that you are going to run into is that the early 2011-2014 FB25 were oil burners. (A good chance is that your Fb25 ran low on oil, which is which it threw a rod.)

You can send both harness to a pro to be merged... step one

 

Step two... open source tune

 

 

would agree with except for one thing which an earlier forum member posted rather critically. the open source tune would have to tune in the fact your borrowed ej is single cam, so that is a substantial tune most people wouldn't be tasked with ever having done. toward this end you could swap in your fb25 harness and splice ej25 connectors into the harness (for such items as coils, sensors, etc.), and most connectors don't need this since they are identical, but this would solve the missing bulkhead connector and probably your starting problem, and it then remains to see if it runs well.

 

alternatively this objection wouldn't apply with the ej255 with dual cams that you could run without a turbo, or just tune in a manually boosted turbo, and then you would just trick your ecu to believe your motour is an fb25 nonturbo with dual cams. i see why there might be interest in going this route, but a sohc downgrade does not make sense unless it was unresearched and/or misinformed--fyi there is a parallel thread on the exact same topic of fb25 swaps in the 4g subfora together with this one amassing members' wisda on the matter) otherwise, your last route to save the title is get 2015+ fb25 that will resolve the oil consumption issue (still need harness splicing at the coils and maybe temperature sensors for oil, water, etc.)

 

otherwise to continue with your setup you need a complete bulkhead harness swap and ecu + biu at the minimum from the same or compatible vehicle engine came from in order to run as sohc, but i have to warn that the other harnesses (instrument, rear wiring, etc.) may need to be rewired, as they are not compatible between legacies and impreza/foresters. it is not just that but the fuel harnenss for the ej25s will require dropping the fuel tank to get to the holes in the back that have connectors. actually for this reason you can go forwards from ej253 to fb25 easily but not backwards since the latter only has connectors that are accessible form the rear seat, and i know this because

 

i actually did the complete motour and bulkhead swap into my 4G L; it is a huge drain on time and requires a tow to and fro for a dealer key registration. I am still working on the vehicle and it is not yet road worthy while i await an ecuflash definition from td-d or whomever for my eighteen codes, but i am happy to say my 4eat swap was plug and play

Edited September 28, 2021 by darthqwo

Surprised you didn't go for the fb20 out of an impreza, where I am located these sell for the same price as the sohc ej25.