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2000 2.5RS/C BRP
2,321 Posts
Discussion Starter #1 (Edited)
So as I just finished my build a few weeks ago, I've noticed that my ECU setup is not original, but generally VERY badly documented.

I run a 2002 WRX ECU (from a manual, not that it matters) with the CarBerry Speed-Density Grp N ROM. It's wired into my stock harness, as my engine is an EJ251 with an M62 on it. It is completely functional, and flashed through the OBDII just like a normal WRX.

Now, You don't need to use the SD ROM. I chose to because I generally dislike MAFs, for a cadre of reasons. Also, my year RS was SD from the factory, so I would have had to buy a MAF. If you DO choose to use the CarBerry ROM, note that while the harness you'll need is any WRX from '02-'05, the ECU has to be an '02 or '03. If you just want to run a standard MAF tune, any ECU ’02-‘05 will work.

Standard blah blah disclaimer: I claim no responsibility for the damage done to your engine, your turbo, your love life, your driver's license or wallet. Just the psyche. :blol:

A large amount of this information comes from Carbotron, who did this and has most of the info. His car was older ('97L) and the wiring was completely different, however, so I had much work to do to transfer it to the RS' pinout.

This is my first point: DO NOT RELY ON PINOUTS. Trace wires, octuple-check against the WIRING DIAGRAMS. It saved my ass more times than I care to mention when things were either left off or incorrect on the pinout.

First, there are some mechanical requirements that you need:

  • WRX Crank Sprocket. This is the (I think) 32-tooth sprocket, used on all EJs since '02 (and in some cases earlier). It's part number 13021AA141, looks like this, on the left:

  • 2005 2.5RS/Phase 2 2.2 Cam Sprocket. This is a little harder to see the difference when installed. The triggers on the back are different, the PN is 13019AA051. Note that there are a few other cars that used the later style despite running an EJ251. Looks like the one on the right (the left is the older style):

  • WRX/P2 2.2 IACV, PN 22650AA181, or 22650AA182. Looks like this:

  • WRX (or STi) Front O2 sensor.
  • Any 5V MAP sensor (the stock RS one will do for NO boost).
  • Any 5V MAF (if you want to run a standard WRX ROM).
  • Any 5V TPS (again, RS stocker is fine).
  • Any IAT. The RS one WILL work, but the wiring is a touch odd. More on that later.
  • OBDII port re-wire. Again, more on that later.
  • Carbotron had to change his cam and crank position sensors, I didn't. He never confirmed if that was due to bad sensors or not. Still not confirmed as of 7/4/14.

Now, in MY case, I did it a little differently. The engine I got was pulled from a friend's crashed 2000 Legacy, and it had all of the cam/crank and IACV/TPS requirements cleared. Apparently some older Subarus used the more modern setup, but I can only verify the 2000 Legacy (2.5). The IM is different, though, as is the wiring, so use the RS stuff. In any case, the absolute simplest solution to the sensor issue is to get a WRX throttle body, since everything is there.

As it turns out, a Phase 2 2.2 has the correct hardware on it. Like, verbatim. So the best route is to get a complete P2 2.2 IM, but the P2 2.2 Throttle Body has all the right sensors and will bolt to a standard 251 manifold.

The wiring itself is pretty straightforward. Most of it is just cut & solder, and in lots of cases the wires are even the same color. I'll include a spreadsheet I made for 2000 RS to 2005 WRX harness. The only difference between the '02-'03 and '04-'05 harnesses that we care about is that two of the ECU connectors swapped numbers, the pins are the same. The harness I used for the ECU pigtails was from a 2005, so my numbers reflect that. If you have an older harness:

2002-3 Conn.
A: B134
B: B135
C: B136
D: B137
E: B84

2004-5 Conn.
A: B134
B: B135
C: B137
D: B84
E: B136

Yep. That's it, just to make it *THAT* much more confusing.

Now, to the notable issues.

The first thing you'll run into is the IACV difference. The '00RS IACV has SIX wires. One is power, one ground, the rest are what I believe to be individual steps in the solenoid's travel. The WRX IACV is only 3 wires, power, ground, and signal. I just chose one of the RS IACV wires and used that. DON'T cut the rest of the wires, they'll be very useful later.

Next, the MAP/IAT sensor. I only include this because it's likely if you're looking at this ECU swap, it's because BOOST. On the RS, the MAP AND the IAT are one sensor. If you're using the stock MAP and IAT, then it's just the pins in the spreadsheet at the ECU end. If, like me, you're changing the MAP sensor (I used a GM 2-BAR for my build), you'll need to do a little wire juggling. First off, the MAP/IAT is four wires. The pins are as follows, from the left to the right if you're looking at the wiring harness connector.

1-Ground. Shared between the MAP and IAT. This should be left connected as standard.
2-IAT signal. This is just a thermistor, so for it to function, only pins 1 & 2 are required.
3-5V power. Shared across many sensors. Required for the MAP.
4-MAP signal. You need pins 1 and 3 hooked up for this to work.

Obviously, if you plan on using a different MAP or IAT, you'll need to cut and redirect those wires to your sensors. I used the stock IAT, the MAP wires are just cut short, and the harness wires lead to my GM sensor.

The Front O2 sensor is next. On the '00 RS, it's an OBDII-tricky twin-signal thing, and it's a sort-of half-wide-band. Real PITA. It's 6 wires, and one of the wires in the O2 connector isn't actually connected to the sensor, it's got some odd voltage divider circuit going on. Since I had a complete WRX harness, I just took the O2 sensor connector off it, and spliced that in, since it's four wires and done.

Basically, the four wires contain some badly worded signal wires. According to the FSM, there's Signal 1, Signal 2, Signal + and Signal -. The 2005 FSM says the Sig 1 and 2 are actually the heater wires. Signal - is just the shared sensor ground. I left the actual signal wires unmarked, however, as you can simply re-use any two of the four shielded wires in the harness. I marked the pins on the actual WRX O2 connector, and what pins they hit on the ECU. You'll just need to match the colors of the wires on each end.

Now we come to the real PITA, the ignition coils. This was the worst part for the others who did this setup. In Carbotron's case, he ended up using LS CNP coils. I know someone else used diodes. I tried the diodes and had no luck, it only ever ran on two cylinders (fired the coil half as often as necessary). I actually tried some really weird stuff, but that's for my build thread.

Anyway, the way I got it to work was by using an OR Gate. This is a digital logic circuit, that took the two individual ECU outputs and fire the coil for either. I built mine out of parts I had laying around, since I couldn't get a complete one locally. I'll give you the basic idea.

An OR gate has five pins. Power, ground, input 1, input 2, and output. I tapped the coil power & ground wires. Then....

ECU COP 1 -> OR Input 1
ECU COP 2 -> OR Input 2
OR Output -> 1 & 2 Coilpack Input (Pin 1 on coil)

This was repeated with a second OR Gate for the other pack (pin 4). If you get a commercial OR Gate, it will be in IC form, which is standardized. I recommend the NXP HEF4071BP,652 (Digi-key link). You only need one of these, it has four OR gates onboard and we only need two. I can give pin numbers for this chip.

Pin 7 - Ground
Pin 14 - Power (+12)
Pin 1 - FROM WRX ECU Coil 1
Pin 2 - FROM WRX ECU Coil 2
Pin 3 - TO Pin 1 on RS Coilpack
Pin 4 - TO Pin 4 on RS Coilpack
Pin 5 - FROM WRX ECU Coil 3
Pin 6 - FROM WRX ECU Coil 4

(Thanks tzedek for noticing I had the 2nd gate's pinout wrong!)

I should warn that I have yet to switch to this IC, so I can't speak for its resilience yet, my home-made gate is more robust but slower. You will need to repurpose two additional wires for the WRX ECU's two additional coil wires. I used the spare IACV wires, hence why I said not to cut them earlier.

Obviously, you can just take the simple solution and get some individual coil packs. Chevrolet LS packs work well, it's what Carbotron uses. I ended up going this route as well, because I had issues with water on my OR gate… And I found 4 LS coils for $50. These are super-easy to wire. There’s keyed power (already in the harness), coil ground (already in the harness) and the trigger wire (one of the 4 trigger wires that are in the harness). The other ground, chassis I believe it’s called, can be tied to the coil ground.

A note on coil packs and dwell: While I don't plan on covering tuning in any fashion (mostly because I have no clue what I'm doing), I will point out that the wasted-spark OR gate setup has a dwell of something near 6.5ms, which is almost double the WRX's COP. So just make sure to change those values in RomRaider, ECUExplorer, etc. It won't seriously impact if you don't, I ran it with the WRX values for a few days, but it should be changed.
Since I switched to the LS-style coilpacks, my map in RR now uses those dwell values. I actually have truck coils, LQ4s to be exact. There is a slightly stronger version, the LQ9. I can provide details about dwell, joules, etc. if anyone would like to use these.

The next wiring weirdness is the Fuel Pump Controller. The WRX uses a PWM unit to slow the fuel pump when not in boost, for NVH and lifetime. I'm still using the stock RS pump, so I just wanted it ON. On the older cars, the fuel pump relay was controlled by switching the power side. On the newer cars (mine included) the relay is controlled by switching ground. That means Carbotron just took the FPC line from the ECU and used it to control his fuel pump relay, I couldn't do that. I had to add another relay, wired like this:

RS FP Relay to switched relay pin 1
WRX FPC wire to relay coil 1 AND switched relay pin 2
Relay switched pin 2 to ground
Relay coil 2 to ground.

Yes, the WRX FPC wire needs to be grounded to make this trick work. No, I can't explain that one. Here's a basic diagram, because this is weird:

I can try to explain this further if need be. The only "downside" to this setup is that it has no prime. As soon as the key is on, the pump is on. It might impact the pump lifetime, but that's it.

The final wiring to attend to is the OBDII port. I swear this one is easy, with one caveat. There's two "line end check" pins. BOTH need to be connected for flashing to work. The problem is that #2 is in the wrong place at the OBDII connector. It's in pin 5, it needs to be in pin 8. I found re-pinning to be really easy, the connector disassembles pretty simply, but I can explain it. The warning is that Subaru WIRES THE OBDII PORT BACKWARDS. I can't emphasize this enough. Basically, if you look up an OBDII port pinout online, you'll go crazy wondering WTF is wrong. Here's how it works, taken from SubieSMART:

The OBD2 standard illustrates the plug with the wide edge uppermost.

\ 01 02 03 04 05 06 07 08 /
\ 09 10 11 12 13 14 15 16 /

But the Subaru wiring diagrams illustrate it with the narrow edge uppermost.

/ 01 02 03 04 05 06 07 08 \
/ 09 10 11 12 13 14 15 16 \
So use the LOWER layout when re-pinning the OBDII connector, or else you'll go freaking insane wondering what's going on...

At this point you're through the worst of it. Now it's worth mentioning that you'll likely have a bunch of wires you won't need. All the TGV rubbish, Auto tranny gubbins, etc. In my spreadsheet, the things you can ignore are in yellow overlay.

Flashing Info:
Anyone familiar with flashing the WRX ECU knows that there's a little connector that has two wires (02-03) or four wires (04-05) that have to be shorted. You might assume, since the ECU harness is being swapped, you need to get the appropriate year's flash block.

Well, you don't! The wires that the flash block connects (one of the line end check wires, IIRC) is already connected. I don't remember for sure if it's already connected inside the harness itself, or if connecting the green plugs connects it (I believe it's this one), but it doesn't matter because it will be connected regardless. Just clip the green test connectors together, and boom, you're ready to flash the ECU.

This is the best I can remember right now. If I recall more, or Carbotron or one of the other four people who've done this have anything to add, please do!

My info is from all over, but thanks primarily to Carbotron and Brydon, whose harness info was indispensable. If you have a different year car, that thread will likely hold all the pin differences. Anyway, I'm out of info now. Maybe. :rolleyes:

(6/8/18 Edit: Fixed some missing images)


2000 2.5RS/C BRP
2,321 Posts
Discussion Starter #9
Well there you go! Good timing on my part, I guess.

*Added a note to the wasted-spark ignition section.

2000 2.5RS/C BRP
2,321 Posts
Discussion Starter #11
Another update. Found the actual printout I used, I marked a few wires that were wrong on my sheet. Changed the appropriate errors, the VSS and Self-Shutoff Control. Hopefully nobody started any swaps yet. ;)

2000 2.5RS/C BRP
2,321 Posts
Discussion Starter #13
Whoo, a 95 would have a LOT of pin changes, and you'd really need an IAT, which I'm fairly sure your ECU won't already have. Not a good reason to give up, just warning you it won't be as simple as using my spreadsheet. Carbotron's should be similar, though.

And now I get to ask a question in my own thread! I'm fiddling with the various inputs for the CarBerry ROM (realized I forgot to attach the headlight switch wire), and the "TID Pin E1" is available. This is something to do with auto-tranny cars, but I can't find this pin listed on the wiring diagrams or the pinouts. Anybody have any clues?

EZ GF w/Curves!
97'OBS/94'SVX LSi/00'OBS/01&#8
8,804 Posts
Thanks I was actually gonna start digging through to make my own write up, proceed, and share results on my 00' OBRS. Slightly different wires but close enough. Food tat all my tech files... Are on a disc... Somewhere... :facepalm:

2000 2.5RS/C BRP
2,321 Posts
Discussion Starter #18
because i wanted to do it for a while.
still don't get -
it is it 02 wrx ecu you're running or 05?
2002 WRX ECU (literally, the first OS tuneable generation).
2005 Harness (identical to a 2002, just different connector numbers like I mentioned). The harness is a bit whatever, since all the WRX ECU connectors are the same until '06 when DBW came in.

Also, the speed density ROM I use is only good for the 16-bit ECUs, the non-DBW ones. Meaning the later ECUs won't work, only 02-05 so far as I know. I do know that 04-05 ECUs have an additional sensor of purpose I have forgotten that will throw a code when it doesn't find it in our cars. Something to do with the fuel system? You can turn it off via RR, just a notable addition.

I don't think self shutoff is required?
Well... My ECU wouldn't turn on without it. It energizes the main relay for the main power supply according to the wiring diagram, and I know the main power supply wasn't turning on for me without it hooked up. I actually found it by tracing the diagram from the supply leads all the way through the relay and noting the relay was controlled by the ECU... Via the self-shutoff pin. I mean, I don't know for sure if the Subaru EE's did it that way on purpose, I'm just going by what I had to do.

Also, it is listed on Brydon's thread. I just missed it the first time through.

05' WRX harness was scavenged
00' RS car
And '00 Legacy throttle body, because it's functionally identical to a WRX one.

2000 2.5RS/C BRP
2,321 Posts
Discussion Starter #20
As long as it has the necessary pins, it should work fine. I had considered doing the same thing, but since the engine side has to be modified as well it wasn't something I considered worthwhile. Why make an adapter for the ECU side if you can't run the old ECU anyway because the engine harness is different?
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