ECU Thoughts and questions

[WingsofWar]

Iv noticed that the tuning options through via legacy factory ECUs are very limited. Iv done some research on pp6 and e-manage for this specific vehicle (00-04 BE/BH). Unfortunately none of those options give me what i want. Basically, fuel and timing tables + datalogging while keeping the vehicle OBD-II compliant. I prefer to have a hand held device for quick MAP preset switches. Unfortunately i believe this does not exist for this car.

Since the car (BE/BH) has the EJ251 similar to the 99-01 Impreza 2.5RS, how similar are the ECUs? For example, If i pulled a 00RS 5spd ECU out of an Impreza and placed it in a 00-04 Legacy 5spd, also assuming i would need to do some rewiring of the connectors or run a patch harness, would it work while retaining OBD-II diagnostics?

I asked this because i see that through rs25.com, various GC8/99-01 owners are running flashed M2 ECUs. or rather, they have a larger selection of tuning options via factory ECU hacking. If i can flash my ECU and reflash, this will allow me to build offline MAPs, and collect Datalogs via OBD-II to USB PC software.

Currently I have no mods, but ECU tuning is a major part of my modifications timeline. I would not want to start adding bolt ons (I/H/E/C) if i cannot optimize them in the future, it would be a waste of time and money personally.

*Notes* Stand alones do not give me the versatility of optimizing factory settings. They require to build a full engine wire harness, then build a base map out of stratch. Iv done this with my FCturbo-II rx7 using Haltech EMS and i Love it. But like most Stand Alone EMS they are geared towards optimizing performance rather than economy. If i were to spend that much money and time on build base maps geared for economy then i shouldn't have swapped out ECU's to begin with.

*notes* AFC units like Apexi SAFC /NEO and HKS FCON are actually very decent electronics to have, I had one in my 98 240sx with a KA24DE-T. They give a basic range of fuel table tuning. I believe units per every 500rpm. This would especially be good for those turbo conversions. If I mated this with OBD-PC datalogging i could ghetto tune this way. Pulling timing mechanically, as SAFCs do not deal with timing. Because of this i would probably tune through EGTs rather than AFRs because im scared of those un-tunable dark spots from not running a more specific tuning system (units per 100rpm+timing). Even then i don't think i could get to optimal tuning with just an Air/fuel controller.


Any thoughts, ideas, directions, experiences, id love to hear it.

[WingsofWar]

More thoughts ~

If i built patch harnesses for plug-and-play 00-04 Legacy and 99-01 Impreza 2.5RS and 2.2L and sets of base maps for Emanage Ultimate and Apexi PowerFC would it sell? What about other EMS tuning options like haltech, hydra, link. Would more and more people incline to mod the EJ251/EJ25D and EJ253 further than just bolt-ons knowing EMS tuning is more easily accessible?

Might be an untapped market to provide aftermarket EMS tuning options to N/A subarus. Especially if there are electronics that already do the work for you, but just don't provide the road map to get there. PP6 does this, but fails as a product all together gathered from amount of lacking software support and users product experience.

[Huffer]

*Notes* Stand alones do not give me the versatility of optimizing factory settings. They require to build a full engine wire harness, then build a base map out of stratch. Iv done this with my FCturbo-II rx7 using Haltech EMS and i Love it. But like most Stand Alone EMS they are geared towards optimizing performance rather than economy. If i were to spend that much money and time on build base maps geared for economy then i shouldn't have swapped out ECU's to begin with.

I think you're quite wrong in this regard. Performance CAN include fuel economy. Having a well tuned engine (and thusly, an ECU map) is one of the common factors between power AND fuel economy. Subaru base maps run rich from factory - this is common knowledge. Many people have proven that you can gain in certain areas by running hotter plugs, better tuned exhausts etc. This all works within the parameters of a factory map.

However, a factory ECU only allows for a limited amount of variability - it learns around certain conditions so as to preserve the life of the engine - bad gas, a poor flowing air filter, even an aggressive driver and the ECU will either dump more fuel or lean it out.

A standalone allows you to tune it for how you want, based on a variable set of parameters - including fuel economy.

[WingsofWar]

*Notes* Stand alones do not give me the versatility of optimizing factory settings. They require to build a full engine wire harness, then build a base map out of stratch. Iv done this with my FCturbo-II rx7 using Haltech EMS and i Love it. But like most Stand Alone EMS they are geared towards optimizing performance rather than economy. If i were to spend that much money and time on build base maps geared for economy then i shouldn't have swapped out ECU's to begin with.

I think you're quite wrong in this regard. Performance CAN include fuel economy. Having a well tuned engine (and thusly, an ECU map) is one of the common factors between power AND fuel economy. Subaru base maps run rich from factory - this is common knowledge. Many people have proven that you can gain in certain areas by running hotter plugs, better tuned exhausts etc. This all works within the parameters of a factory map.

However, a factory ECU only allows for a limited amount of variability - it learns around certain conditions so as to preserve the life of the engine - bad gas, a poor flowing air filter, even an aggressive driver and the ECU will either dump more fuel or lean it out.

A standalone allows you to tune it for how you want, based on a variable set of parameters - including fuel economy.

The point being, spending $1k+ on a Stand Alone EMS to attempt to optimize stock N/A application boxer4 regardless if its performance and economy, might not be cost effective option. Typically individuals and tuners alike who hit walls in tuning (eg. piggyback/ECU FLASH) will go standalone. And the reason they hit those walls is because they require specific or more parameters to support their modifications. Its true tuning for fuel economy could indeed co-inside with performance and vise versa, especially when using AFRs to tune. But I don't believe that a person should go as far as a Stand alone ECU on a factory vehicle to get the most out of an unmolested engine piggybacks do more than enough in that department for half the cost. The Factory ECU does for the most part do a pretty decent job in compensating for basic mods, and could use very small adjustments in tuning.

Which is why I say, Stand alone is geared towards performance, i did not say it could not do either of the two. On a personal note, I would run a Stand alone if i had plans on making power a priority. I guess i have been spoiled by my rx7, as economy tuning damages the engine. Running Rich/Stoich AFRs on a rotary causes catastrophic engine failure. They perform the best and give the best MPG at 10.5-11.5 AFRs which is pig rich in piston engine tuning especially in N/A piston tuning.
Tuning my 240sx for a bit more economy was a bit trick, as the turbo responded well rich mixtures but start to fall flat in power when i start to pull fuel for better economy. It took a few dyno pulls to find the best medium ground between performance and economy.

[Huffer]

Performance is relative - you give up some fuel economy to make horsepower, everyone knows that. The reason the Subaru ECU isn't ideal to achieve maximum power and/or fuel economy is because it self-learns around any signal that isn't wide open throttle. This is why you won't find many people trying to decode/flash the stock ECU. It's just not worth it.

If you are trying to max out the fuel economy of the Subaru engine, you're not going to do it. Don't you think that FHI's engineers would have already come up with a tuning solution that give a base 2.5l engine better than 27mpg freeway?

The limitation isn't just in the tuning - it's also in the mechanics of the engine.

[jey]

Fuel economy is taken into account when FHI engineered the tune, but it may not have been the highest priority. Safety/reliability is probably higher, which is why the stock tune runs rich. You CAN get better economy - but at the expense of something else.

[anothernord]

The best piggyback tuning system for any locked-down ECU is definitely the Emanage Ultimate. It can control pretty much everything, and has lots of flexibility for changing stuff in the car.

I find that the stock EJ25D ECU targets a 14.3 AFR under closed loop; obviously not ideal for fuel economy. My way to get past this is using an Innovate LC-1 wideband system, where one of the outputs is wired to the ECU's O2 sensor input. I can tweak the voltages to trick the ECU into thinking it's getting the AFR it wants, while actually running at true stoic. I actually have it targeting a 15:1 ratio under closed loop, and it works great. I'm still getting MPG data.

[DarkPhoenix]

The best piggyback tuning system for any locked-down ECU is definitely the Emanage Ultimate. It can control pretty much everything, and has lots of flexibility for changing stuff in the car.

I find that the stock EJ25D ECU targets a 14.3 AFR under closed loop; obviously not ideal for fuel economy. My way to get past this is using an Innovate LC-1 wideband system, where one of the outputs is wired to the ECU's O2 sensor input. I can tweak the voltages to trick the ECU into thinking it's getting the AFR it wants, while actually running at true stoic. I actually have it targeting a 15:1 ratio under closed loop, and it works great. I'm still getting MPG data.

I have one of those lying around in my closet. I had it for my VR4, but never got a chance to install it. Time to look into that as another option for keeping the car from running so rich.