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Swapping a phase 2 ej25 in an older legacy or impreza

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I recently finished a swap of a 99 forester 2.5 into my 90 legacy sedan and have had quite a few questions about how I did it and problems I ran into. So I figured I would write up a little thing about some of the problems I ran into.

As most people may know if you been around Subarus long enough, they are like legos. Everything damn near fits in everything else.

The motor swap its self was a piece of cake. It was no harder to put in then any other EJ motor.

These were a few things that I needed to be deal with before it ran like butter.

Throttle Body

I ended up using my 2.2 throttle body rather then the 2.5 one. Mainly for ease and not much BS. The throttle position sensor is different and I didn’t want to go through the hassle of repining or trying to make the 2.2 TPS fit the 2.5 TB. The main difference between them is the lack of an IAC on the 2.2 TB. And because the 2.2 TB doesn’t have that I had to make a plate to block the extra area on the intake that is there for the IAC on the 2.5. I just used a 2.5 gasket, then the plate, then 2.2 gasket then the 2.2 TB. I also smeared a little rtv to loose any small air leaks. Other then the plate the TB bolts right on and the throttle cables mount up just fine. Just so you know both the 2.5 and the 2.2 have the same size throttle plates, so from an air flow stand point there is no difference.



Injector plugs

In the picture below you can see the injector from a 2.2. "A" is where the 2.2 ears are and "B" is where the 2.5s are. So how did I fix this, I just cut off the ears. After they were gone the harness plug clicked right on and didn’t seem to care that the ears were gone.


Coil and plug wires

This was one that took me a little time to figure out. Ideally I would have wanted to use the 2.5 coil pack mainly because the plug wires would match up to it and the heads. But after trying to repin and use the 2.5 coil I could never get any spark. So I had to resort to using the 2.2 coil. Using the 2.2 coil created a different problem in it’s self. The coil pack from the 2.5 have tips like a spark plug and the 2.2 have tips like a distributor cap. I was able to split the boot that was on the plug wires at the coil and bend the tips to hold themselves into the 2.2 coil. Then I found some rubber boots that are for the 2.2 coil style and slid them over the wires for that factory look.

So you may ask, why don’t you just use the 2.2 wires? Well on the 2.5 heads they recess the spark plugs in so far in that you need the plug wires from the 2.5. The 2.2 wires just wont reach. That and the mounting place for the coil is off set towards the passenger side. So two of the wires are longer then the other. Where as the 2.2 wires basicly have 4 wires that are the same length.

I also had to make a little bracket to mount the 2.2 coil because the mounting holes between the 2.2 coil and the 2.5 coil are different.




Evap system

Newer Subarus have their charcoal canister back by the gas tank and the older ones have them under the hood. For this one I really just had to copy the vacuum lines that were on the underside of the 2.2 intake and remake it on the 2.5. I ended up using some of the metal hoses from the 2.2 intake and connected them all with some vacuum hoses. Also I swapped the solenoid from the 2.2 on the 2.5 so it would just plug into the harness.

Wiring Harness

The wiring was pretty easy. I just snaked the whole harness off of the 2.2 intake and snaked it into the 2.5 intake. Threw a few zip ties on to keep it in place and that was all done.

Temp sensor

Newer subarus use only one temp sensor where as the older ones have two. One for the gauge and one for the computer. Under the intake is what I would call the water crossover tube. I don’t know what it is really called but if you saw it you would know what I was talking about. On the 2.5 tube it only had one sensor but was not drill out for the second one even though the casting was still there. So what I did was take the tube off of the 2.2 and put it on the 2.5 with some new O rings and I was done. No need to swap sensors because I brought both that I needed to the new motor.


Cam and crank sensors

These were just an easy swap. Take 2.5 out replace with the 2.2s. Snake wires to the back and you are done.



Oil pressure sending unit

This was an easy part also. Simply remove the oil pressure sending unit from your 2.2 and put it in the same spot on the 2.5.


Knock sensor

Just take your 2.2 knock sensor and put on the 2.5 block.

All of the brackets for the alternator and power steering pump and AC pump just bolt right on. All the holes are in the same spots on both blocks. The only thing I ran into was the power steering lines got in the way of the now bigger intake. So just a little bending of the hard lines and all fit great.

Things to keep in mind if you are doing this swap.

With this combo you not have a working IAC. The 2.2 IAC was mounted on the side of the intake and the 2.5 was mounted with the TB. So by using the 2.2 TB and the 2.5 intake, I no longer have a place for an IAC. Come to find out this really wasn’t a big deal. When you first start the car it will want to die if you don’t put your foot on the gas. I generally just hold the RPMs at about 1500 for 30 seconds and after that it will idle. First low because it’s cold, but once warm you really can’t tell there isn’t one. I have my idle set at about 1000 and it will sit at that all day. Now this is something I am willing to live with. This being my race car, cold starts are the least of my worries. Also if you still have AC the ECU will not be able to compensate for the draw from the AC pump. All of my AC stuff is removed so no biggy for me.

Now there is rumor that some older JDM WRX intakes will bolt up to the heads and still uses an IAC mounted to the side of the intake. I was never able to confirm this rumor as finding an intake from a JDM WRX is not something I have ran across.

Also this is not a problem if you do this swap to a 1.8 impreza as the 1.8s have the IAC mounted on the TB.

One idea that I came up with on how to have an IAC in the legacy was to use a 1.8 TB. The IAC on the 1.8 and the 2.2 do have the same plug but I’m not sure if the 2.2 ECU would run the 1.8 IAC. One thing to note the 1.8 TB is smaller then the 2.2. Not that this would make a large difference but there is a difference.


What about the crappy 2.5 head gaskets?

Yes I knew before getting into my swap that the ej25s have a pretty bad rep of head gaskets issues, from blowing them in the phase 1 to leaking coolant in the phase 2. So to give the best chance to my motor I started with a plan of parts that have proved themselves to be reliable. As far as I know Subaru has stepped up and now make a decent head gasket. But I had been doing a lot of reading about a company called Cometic. And from what I hear they make some pretty outstanding gaskets. And the funny part was they were no more money then if I was to go to Subaru and get a set from them. So with a set of Cometic head gaskets and a set of ARP head studs I put the top end together. I feel this combo should give me quite a bit of extra protection. Only time will tell but so far so good.

So would I do it again?

Hell yeah. This what these old legacys should be like. It has way more pickup and go and go and go. I would even deal with the idle problem on a street car. But if I was to put it in a street car I would look further into using the 1.8 TB so I could have a better cold idle and bump up the idle if I turned on the AC.

One more thing to mention is that the older 2.2 and 1.8 ECU had a much steeper ignition curve then the newer bigger motors. So it tries to put more timing in then it should and can cause knocking. In the 2.2 you are safe because it has a knock sensor and will pull timing if it hears any knocking. The 1.8 does not have a knock sensor so the safe thing to do is run 92 octane. In my case my car on 87 octane, ran, and pulled hard until you reached the upper end of the RPMs. Then it felt it was running less then it should be. So I ran a tank of 92 through it and it is a whole new beast. It pulls hard all the way to redline and doesn’t have that feeling that it did before. So unfortunately it has an expensive drinking habit now.

Now as you can tell this is by no means a step by step “how to” kind of write up. But these will get you through the main things that I had to deal with. I would be more then willing to answer any questions about my swap. So feel free to ask away.

As of writing this I have got about 300-400 miles on this set up. And it's still running great. Nothing weird going on except for the cold starting thing that I knew was going to happen. Well except for the crazy exhaust rattle that is driving me nuts. But that has nothing to do with the swap, that's more because I bent it at the last event and I need to replace it.

Edited by mellow65
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