legacycentral bbs

'98Wagon wrote:I guess I was under the impression that a piggy back would alter the signals to the factory ecu to allow it to work around the boost. Good to know that is not the case.

'98Wagon wrote:Another question for you guys-if I were to pick up STI or at least a turbo ECU, would i be able to use the sensors from any OBD II motor to work with that ECU? Or would I need to pick up the sensors specific to that ecu?

I am sorry if this seems like its got an obvious answer, but I am so unfamiliar with electronically tunes cars, that I am just trying to figure out the basics.

'98Wagon wrote: My questions:
-if I put 25d heads on my block, and keep the sensors that come on that motor, I will be OBD II right? (Do these heads make my motor an interference motor now?)(what sensors does the 25 have that the 2.2t not have?)

>>>Still OBDII and you'll need the Intake Manifold as your SOHC won't fit the DOHC (sensors are the same as is the throttle body, but fuel rails are different). The engine becomes interference as the valves CAN collide, since there's intake and exhaust on separate cams now. I'd guess you could also hit the pistons. For the oil/coolant you can tap into the oil pressure/sender behind the P/S for the oil or used the existing oil source on the DOHC head (search on here) and put a return into the valve cover. For the coolant some have used the heater hoses.

-the above should pretty much be plug and play with my ecu right?
>>>>Yes, you could run the EJ22T or EJ22e w/the EJ25D heads w/the stock ECU, but of course w/the EJ22T your CR is about 7.5:1 which would sux w/an NA engine

-if I run a piggy back such as a GReddy emanage or similar, I should be able to have some tuning ability while still using the factory 2.2 ecu from my car, right? (Or am I totally wrong on my thinking here?)
>>>I'm the Forester guy that Josh/Legacy777 mentioned and yes I did have issues, but I got my setup from a guy on NASIOC that ran it successfully on his '98 LGT w/an EJ20G engine (same ECU as my '98 Forester). LINK to my Foz project. I will admit that I never did figure out whether I had a mechanical or ECU/electrical issue w/my Greddy EMU setup.....so may not be a fair reference....although I generally agree w/Josh about piggybacks, there are NO easy options for the '95-'01 Subarus as there were no turbo models in the US during those years to borrow from. Because of that I think if you are wiring-savy and MOST important - know a tuner that can tune the Greddy EMU, it's not a complete waste to consider it....but many just go w/the full WRX swap option (as did the guy w/the '98 LGT when he went for 400HP). Also, check out Megasquirt, but that's a REAL big jump for wiring/sensor/etc.

>>>I also think you should spend some time researching Brakes and Suspension b4 getting too greedy in the HP category. Spend some time on here or LegacyGT to find out what is easiest/cheapest to install.

I've provided a link to the 2002 WRX ECU I-O for your reference, and I’ve gone down the list for my comments below.

http://www.main.experiencetherave.com/s ... CU_I-O.pdf

• Crank position sensor – You need to use the WRX sensor
• Cam position sensor – You need to use the WRX sensor
• Throttle sensor – You need to use the WRX sensor
• Rear oxygen sensor – You can probably turn this function/code off in the ECU via one of the Open ECU programs
• Front oxygen sensor – You need to use the WRX sensor
• Engine coolant temp sensor – You need to use the WRX sensor
o If you plan on keeping the legacy gauge cluster you will need to either tap the coolant crossover or figure another method to get the single wire coolant temp sensor in the coolant so it can be used for the dash temperature gauge.
• Vehicle speed sensor – The speed signal being output by the legacy gauge cluster will work fine to be inputted into the WRX ECU
• MAF sensor – You need to use the WRX sensor
• IAT sensor – You need to use the WRX sensor
o I’m pretty sure this is integrated into the MAF sensor so as long as you use the WRX MAF you should be fine
• EGT sensor – You need to use the WRX sensor
• Tumble generator valves & position sensors – The consensus I’ve heard is these are only used for startup emissions reduction. You can by the TGV deletes and probably disable the code in the ECU with Open ECU (I’d look into this a little more and see what the WRX & STi guys do
• Wastegate control solenoid valve – The Legacy valve is a better setup, however to use it the ECU will need to be tuned & setup to use the blocking type valve vs. the bleed style valve. I would use the Legacy valve and just have things tuned to use it.
• Starter switch – This input is the same whether you use the Legacy starter or WRX starter, it’s just a one wire output from the starter to the ECU
• AC switch – Same thing as the starter switch, this will come from the Legacy HVAC and is already on the Legacy ECU, you just need to map it over to the WRX ecu
• Ignition switch – same thing as above with the other switches
• Neutral position switch – Same as the legacy neutral position switch
• Test mode connector – I believe these are green on the WRX and would be part of the harness
• Knock sensor – You need to use the WRX sensor
• Back-up power supply – The legacy ecu has this and just needs to be moved over
• Control unit power supply – The legacy ecu has this and just needs to be moved over
• Sensor power supply – I’m not sure what this is, I’d have to look at the wiring diagrams to see
• Line end check 1 – Same thing as above, I’m not sure what this is and would need to look at the diagrams
• Ignition control – You need to use the WRX coil on plugs
• Fuel injectors – You need to use the WRX injectors or if you go bigger the new injectors need to be calibrated in the ECU & have the latency values updated
• Idle air control solenoid valve – You need to use the WRX valve
• Fuel pump controller – You need to use the WRX fuel pump controller
• AC relay control – This is the same as the legacy
• Radiator fan relay1 control – The legacy only has one relay control (I’d have to look at the WRX and how the two different relay setups are configured
• Radiator fan relay2 control – See relay control 1
• Malfunction indicator lamp – This is the check engine light and is the same as the legacy
• Engine speed output – This is the tachometer and should be fine going to the gauge cluster tach
• Purge control solenoid valve – This is the same as the legacy
• Torque control 1 signal – I’m not sure what this does and would need to look at the diagrams
• Torque control 2 signal – I’m not sure what this does and would need to look at the diagrams
• Torque control cut signal – I’m not sure what this does and would need to look at the diagrams
• Fuel temp sensor – You will need to add this sensor and wiring
• Fuel tank pressure sensor – You will need to add this sensor & wiring
• Fuel tank pressure control solenoid valve – You will need to add this & the wiring
• Drain valve – I’m not exactly sure what this is for, but you’ll probably need to add it
• AT diagnosis input signal – If you are MT, then you don’t need to worry about this
• AT load signal – Same as above, don’t need to worry about it
• Pressure sensor – You need to use the WRX sensor
• Fuel level sensor – I’m not sure why the ECU is getting this signal and would need to investigate it further
• Small light switch – I’m not sure what this is for
• Blower fan switch – I’m not sure why the ECU cares about this
• Rear defogger switch – I think the ECU is programmed not to leave the rear defogger on too long, you would like need to bypass this input and not use it
• Power steering pressure switch – If you use the WRX pump, you’ll just need to wire this switch up
• Front oxygen sensor – As mentioned above, you need to use the WRX O2 sensor
• SSM/GST communication – This is for the Subaru select monitor
• All the grounds – These are all the various grounds


You either need to pull the dash and try to use the WRX harness as much as you can or you need to figure out how to use the existing Legacy harness and merge the two where it’s needed and add the extra wiring where it’s needed. Some of the hardware and sensors like the fuel tank sensors is going to be rather difficult to retrofit to the Legacy tank.

Some of these reasons are why you don’t see too many OBD2 swaps in OBD1 cars. There are significant differences in wiring and sensors. I want to make sure you are as educated as you can be going into this. What year WRX are you using as your donor? Do you have all the wiring diagrams?

Let me know if you have any questions.