EJ20 - EJ25 Swap

[xkalib3r]

Hi All,

First a bit of background.

I have a 1997 Subaru Legacy GL Wagon, which came stock with an EJ20 engine. In South Africa where I am from, this is so far the very only one I have come across thus far...

Alright, so eventually I got sick of fixing oil leaks, and servicing more than I should have to, and got myself an EJ25 to put in the car. After much reading and asking around, I have established that the engine I bought is a 1997 EJ25D (JDM Spec i presume).

Well, I managed to get some help from a few friends, and we installed the EJ25 with not too much difficulty.

Once this was done, it was off to the shop to get custom branches and free flow exhaust fitted.


So, she starts and drives...But.... (This is where I would really appreciate some help)

1. The car is using fuel at a rate of knots - I have replaced the Throttle Positioning Sensor with that of my old engine. The car is running much more smoothly, but is still using too much fuel and you can still smell too much unburnt fuel when she idles. (Service manual says TPS (Fully closed) should have a reading of between 0.2V - 1.0V I have adjusted it up and down (And it does make a difference) but such a large range makes it hard to set.

2. The car has issues starting - If the car has been sitting for some time, It has to turn over far to many times until she eventually starts. However, if I start the car, let it run for a few seconds, or drive a few miles, then leave it off for a minute (Run into the shops) and come out, it starts almost perfectly.
I have checked that Crank Positioning sensor, and if I disconnect that, it will not start at all. I have heard that the knock sensor might cause this (I still need to try test it this weekend)


If there is any insight or advice that anyone could offer, I would very grateful!

If there is any more info that is needed, please don't hesitate to ask

[Legacy777]

Welcome to the BBS.

Based on your description of the problem, I would suggest replacing the coolant temp sensor. It should be the same as what you had on your ej20 engine. The sensor has a brown plastic connector and is located in the coolant crossover pipe under the intake manifold.

The TPS on the newer cars adjusts itself based on readings taken during startup, so I wouldn't get too worried about it. Try replacing the coolant temp sensor and see if that helps things.

[xkalib3r]

Hi Josh,

Thanks for the info. I will try get the old one as soon as I can (Work is a little hectic at the mo)

Will report back once this is done.

[xkalib3r]

Super late reply I know! My bad...

So I replaced the coolant temp sensor with a known working one but it has not changed anything sigh...


Since my last post I have established a few more things.

1. Im certain my head gaskets need to be replaced - Which will hopefully be done soon

2. Biggest issue is this. My old motor was an EJ20 SOHC. The new one is the EJ25 DOHC- Presumable y also OBDI as wiring all matched up 100%

This being the case, my biggest issue is that my ECU is going nutz because of the SOHC-DOHC - Any ideas? Does anyone know where I could get even a stock EJ25DOHC ECU?


Thanks in advance

[Legacy777]

The ECU shouldn't really care about the SOHC vs DOHC. What it likely cares about is the cam/crank signals its getting. I'm not sure what the base timing is or what the cam/crank triggers are like in comparison to the SOHC setup.

Can you be a little more descriptive as to what you mean by "my ECU is going nutz..."?

[letdown450]

You need to change the cam and crank gears from the old engine to the new otherwise your firing sequence will be off. make sure that the sensors match because some pick up differently than others.

[wtdash]

Hi and Welcome to the LC site.

Please note the dates in the upper right corner of each post to see the most recent. This Thread is over 4 years old and the original poster (OP) never replied after the last question.

TD