1993 EJ18 ECU ~ ROM ID: 733C21

[RoadRunner]

Hi all,

I have a US-Spec OBD1 1993 Subaru Impreza Wagon.  Originally came with the EJ18 but I replaced that with 1999 Impreza 2.5 RS Engine a few months back.  However, I am running the EJ253 on the original EJ18 ECU.

Today I successfully communicated with the ECU & TCU (4EAT) through the Hex Com Tool linked on b3lha's site, though got different results than what was listed.  I imagine those numbers are for the SVX.

I also got EvoScan up and running.  I seem to have the TPS, MAF, and coolant temp working.  I'm getting numbers on other things too, but I don't know if those are accurate readings yet.

The ROM ID for this 1993 EJ18 ECU is 733C21.

If someone would be willing to guide me, I could possibly get more info from it.  I'm not exactly a computer genius, when it comes to stuff like this, so bear with me!

Cheers!

[bubba2533]

What cable are you using?

[RoadRunner]

I'm using the 9-pin SSM to USB cable from limitless.co.nz

[seport]

I have a US-Spec OBD1 1993 Subaru Impreza Wagon.  Originally came with the EJ18 but I replaced that with 1999 Impreza 2.5 RS Engine a few months back.  However, I am running the EJ253 on the original EJ18 ECU.

So The EJ25 engine is running with EJ18 ECU?
Does the EJ18 ECU have inputs for the knock sensor and cam shaft position sensor, apart others?

If someone would be willing to guide me, I could possibly get more info from it.  I'm not exactly a computer genius, when it comes to stuff like this, so bear with me!

If what you need is the address parameters, then I will search for your ROMID in my SSM, if I have it, I can extract the correct parameters.

[RoadRunner]

So The EJ25 engine is running with EJ18 ECU?
Does the EJ18 ECU have inputs for the knock sensor and cam shaft position sensor, apart others?

Yes, it actually runs quite well off the EJ18 ECU, even with Delta 2000 camshafts.  I ordered a JDM OBD-I EJ25D ECU tuned my Mines a few weeks ago to replace the EJ18 ECU, but it may be a while before I get that installed.

The EJ18 ECU does not support a knock sensor.  It does use a camshaft position sensor though, plus crankshaft position sensor, TPS, IACV, water temp sensor, and all the other essential stuff.  If you compare the list of pinouts to, say, a 2000 Impreza 2.5 RS engine, the list is about half as long, due to less sensors throughout the car.

If what you need is the address parameters, then I will search for your ROMID in my SSM, if I have it, I can extract the correct parameters.

That would be awesome!

[seport]

hi,

sorry for the delay, but i have some problems with linux again!, I will get back to you later this week.

[seport]

here are your address parameters for ECU - ROMID 733C21

116C Battery Voltage
1075 V. Speed
1073 RPM
11AC Coolant temp.
1323 Ignition Timing
1307 MAF
1305 Engine Load
1329 TPS
1306 Injection Pulse Width
1314 ISC Valve Duty Ratio
1310 O2 sensor
1332 O2 Max.
1333 O2 Min
10A7 A/F Correction
12CF EGR Temp

Alex

[RoadRunner]

Thank you Alex!  I will test those out this weekend!

[b3lha]

Nice work Alexander! 

[RoadRunner]

Okay, I lied.  I tested the parameters tonight, and they all seem to work!

Actually I can't verify the EGR Temp, because my car doesn't have that sensor (only came on some EJ18's).  And even if it did originally have it, I would have had to remove it for my EJ25 swap.

I only let the car idle, and revved it a little, so I also didn't test the Vehicle Speed.  Though it did remain at zero while parked.

One question - what are the units for 'Engine Load'?  Is it just a percentage?  It displayed between 19-23 at idle, and increased as I revved.

Thanks again, Alex!

Cheers
Corey

[seport]

One question - what are the units for 'Engine Load'?  Is it just a percentage?  It displayed between 19-23 at idle, and increased as I revved.

There is no units for engine load, the diagnostics manual does not specify any unit. I believe (and it is only my opinion) that it is just a number from 0 to 255 which the ecu use for the various maps so that it can produce an appropriate output.

What formula are you using for engine load? There shouldn't be any it is just conversion from hex to decimal.

For the EJ18 it should be 40 - 70 at idling after warm up, but you have different engine EJ25, I don't have any specifications for that motor.

[RoadRunner]

EvoScan has the Engine Load formula as 'x'.  So, you're right, there is no real 'formula' for it.  Just a conversion from hex to decimal.

Do you know if all/most Subaru ECUs use the 0-255 range, or is that specific to the EJ18 ECU?

[seport]

Do you know if all/most Subaru ECUs use the 0-255 range, or is that specific to the EJ18 ECU?

Sorry I don't know , however if the ECU is 8 bit and there is no conversion formula to read the output, then it can not be more than that.

0x0000 to 0x00FF which is 0 to 255

Don't get me wrong, but I am still wondering about the knock sensor and the cam shaft position sensor of your motor EJ25 and how did you interfaced them with the EJ18 ECU.
As you can see from the address locations which I extracted from the SSM it does not cater for knock correction, which is a parameter found on ECU's with knock control.
It is nice to know some more details about this swapp, since I might consider replacing my motor EJ15 with EJ20 (if I find something worth it) without the need to change the ECU etc.

[RoadRunner]

Gotcha!  I don't know a lot about this hex, bit, baud stuff...

As for the swap, everything (harness-wise) from the ECU up to the 2 SMJ connectors at the bellhousing is original, untouched EJ18.  I also used the original EJ18 harness that runs under the intake manifold, though I had to make a few changes to it...

1) Injector plugs - used EJ25 injector clips on the EJ18 IM harness.  Had to make sure i got the polarity right.

2) Water temp sensors (on the coolant x-over pipe)- EJ18 uses two of them.  One that is larger, 2-pin, and is used by the ECU.  And a smaller one with a single spade connector, used for the coolant temp gauge in the cluster.  The EJ25 uses only one 3-pin coolant temp sensor, which serves both the ECU and the cluster gauge.

I had two options here:
a) [what I chose to do] Install both EJ18 sensors on the EJ25 coolant x-over pipe.  The EJ25 x-over pipe had a plug installed where the smaller, spade-connector sensor goes.  The larger, 2-pin sensor swapped directly in place of the EJ25 3-pin sensor.  Which made it so that the EJ18 harness plugged right in.

b) [the other option] Use the EJ25 3-pin sensor, and install the 3-pin connector on the EJ18 harness.  The wire from the spade connector sensor matches up to the bottom pin of the 3-pin connector.

3) EGR solenoid - The EJ25 didn't have EGR, but the EJ18 did, and the EJ18 ECU still expected the solenoid to be there.  So, I just connected it (to prevent a CEL), and bolted it to the IM.  No hoses go to it, and it doesn't control anything, but the ECU doesn't know any better.

4) Coilpack & plug wires - There are a few options here too...

a) [this is what I did] Make brackets to mount the EJ18 coilpack on the EJ25 manifold.  (The bolt holes don't line up).  Use EJ25 plug wires, but cut half the rubber boot off the coilpack end.  This will allow the EJ25 wires to plug into the EJ18 coilpack.

b) [this is what I am going to do] Remove & bypass the ignitor on the firewall, use the EJ25 coilpack, unmodified EJ25 plug wires, and splice an EJ25 coilpack connector in place of the EJ18 coilpack connector on the EJ18 IM harness.

Everything else is plug-n-play, including:
-Camshaft sensor
-Crankshaft sensor
-Idle Air Control Valve (used the EJ18 throttle body to keep it plug-n-play)
-Throttle Position Sensor (again, used the EJ18 throttle body)
-Vapor Canister Purge Solenoid (I removed this system from my car, so it's like the EGR solenoid - doesn't control anything)

Knock sensor was not found on the EJ18, and the EJ18 ECU doesn't expect to see a signal from one, and doesn't support it.  The EJ25 used a knock sensor, but is not necessary to run.  As a result, the timing is probably not as aggressive as it would be with an EJ25 ECU and a knock sensor.

The only thing to watch out for, if you do this (or any) NA to NA swap, is to make sure the tooth count on the crank and cam gears are what the ECU you are using expects to read.

I used the EJ18 airbox, MAF, intake tube, and throttle body.  Pretty much everything else is EJ25, except what I listed above.

This info doesn't apply to all EJ25 swaps, so take it all with a grain of salt.  Mine specifically was a 1999 Impreza RS EJ253.

Cheers

[seport]

Thank you for your detailed report.