Hey folks,
Wondering if we have any Subaru junkies out here. Long story short - I am a practicing licensed automotive tech and this issue has me at a bit of stand still/brainstorming period for about a year. Not the end of the world - car runs fine, but if I could solve this issue I'd be very happy.
2001 Subaru Legacy GT Limited Sedan
Automatic Transmission
EJ251 (ORIGINALLY)
EJ203 Swapped Engine
My wife's car, typical Subaru EJ251 BS, head gaskets failed, coolant emulsion, I procrastinated it for too long and motor got sludged up pretty badly. No big deal, did some homework on the topic, although a bit of a horsepower loss, I swapped in a JDM EJ203 motor (proprietary to Japanese market - never produced for US market at all). Basically the idea behind this swap is that you get although a less powerful NA motor, a more reliable one, with a marginally larger deck surface for the head gaskets, and the JDM motors had MLS head gaskets VS the failure prone junk they put in the USDM 2.5L NA motors.
Anyways, had to have been the EASIEST engine swap I have ever done in my career, 1.5 hours to have the motor laying on my floor, stripped to a short block. As for the donor motor, basically the only thing you are after here is the long block assembly, the JDM variant has a vastly different fuel rail, injectors, a variable intake manifold, fly by wire TB, MAF vs MAP air metering, etc etc. The basics are that you swap the USDM thermostat assembly, cam/crank gear(s) as the reluctor patterns are different, and a couple other knick knacks, etc. So I did my thing, freshened it up accordingly, new timing components, plugs, etc. Got it in, thing runs perfect, zero issues with drivability, noticably less power but very very happy and it cost me very little money. I have had this engine in the car for a years time now.
After getting some drive cycles completed right after install I started to notice a P0170 - fuel trim "malfunction" DTC that would recur after 2 x drive cycles. Never had this issue for the multiple years I owned the car prior, and have previously logged data and know the fuel trim was never an issue prior. I followed Subaru's service information diagnostic flow path, that takes you to an ending of "replace PCM". Smoke tested everything, verified fuel pressure, A/F sensor, etc etc etc everything is working 100% as designed. I then started to log some data on it, and noticed my LTFT is consistently -20% indicating the ECU is pulling 20% of fuel out of the map to make lambda. This is the case at idle and through the RPM range anytime you are in closed loop. Then I do some digging into this topic and find that many if not all guys doing this swap are experiencing this. Then I think to my self hmmmmm, I just swapped in an engine with exactly -20% displacement relative to the original motor. So this code makes sense, 20% less displacement should in theory require 20% less fuel to be running stoichiometric. The DTC conditions for setting match the data the ECM is showing me (I believe it was a fuel trim in any direction in excess of 18% - pulling from memory here don't quote me). So I talk to a world renowned tuner who happens to live about an hour from me here in Alberta, Canada (Wester's Garage) and he is telling me sorry there is nothing we can do with the ECM to remap the fuel, it's too old. He suggested using the 2.0L JDM fuel injectors, albiet they are top feed style injectors like the USDM ones, they are of a different size and configuration and 100% not compatible at all. We had tossed the idea around finding an injector that would fit this car that is 20% smaller cc than the original 2.5L injectors. The issue I am finding is that the original 2.5L NA EJ251 motor is about the wimpiest thing Subaru ever produced of the era in theUS market and I am not savvy enough on Subaru interchangeability to know what injector would fit what. I am thinking I will have a very difficult time finding an injector SMALLER that these OEM 2.5L ones in the car currently especially ones that would be a direct swap.
Aside from installing a stand alone fuel management system (ridiculous expense for a wimpy stock car hah), I think that finding an injector of 20% less cc would likely work, as presumably the PWM of the injectors would then match the factory injector (when installed in a 2.5L engine) and I would think the fuel trim would come back into some normality or at least the typical +/- 10% area I would like to see it in where it will not trigger a fuel trim malfunction code.
If anybody has any experience with this swap and any ideas on combatting this, please advise. I had thought about an adjustable fuel pressure regulator (OEM one is vacuum reference and does work properly I did test it) however I don't believe this will help me in all areas (at idle as well as throughout closed loop RPM range). I don't think this will be an accurate enough modification to eliminate this issue. If I could tune the factory ECU I could easily solve this problem, and no the JDM ECU will not work either (much different engine management systems used on JDM motor).
Thanks in advance!
Wondering if we have any Subaru junkies out here. Long story short - I am a practicing licensed automotive tech and this issue has me at a bit of stand still/brainstorming period for about a year. Not the end of the world - car runs fine, but if I could solve this issue I'd be very happy.
2001 Subaru Legacy GT Limited Sedan
Automatic Transmission
EJ251 (ORIGINALLY)
EJ203 Swapped Engine
My wife's car, typical Subaru EJ251 BS, head gaskets failed, coolant emulsion, I procrastinated it for too long and motor got sludged up pretty badly. No big deal, did some homework on the topic, although a bit of a horsepower loss, I swapped in a JDM EJ203 motor (proprietary to Japanese market - never produced for US market at all). Basically the idea behind this swap is that you get although a less powerful NA motor, a more reliable one, with a marginally larger deck surface for the head gaskets, and the JDM motors had MLS head gaskets VS the failure prone junk they put in the USDM 2.5L NA motors.
Anyways, had to have been the EASIEST engine swap I have ever done in my career, 1.5 hours to have the motor laying on my floor, stripped to a short block. As for the donor motor, basically the only thing you are after here is the long block assembly, the JDM variant has a vastly different fuel rail, injectors, a variable intake manifold, fly by wire TB, MAF vs MAP air metering, etc etc. The basics are that you swap the USDM thermostat assembly, cam/crank gear(s) as the reluctor patterns are different, and a couple other knick knacks, etc. So I did my thing, freshened it up accordingly, new timing components, plugs, etc. Got it in, thing runs perfect, zero issues with drivability, noticably less power but very very happy and it cost me very little money. I have had this engine in the car for a years time now.
After getting some drive cycles completed right after install I started to notice a P0170 - fuel trim "malfunction" DTC that would recur after 2 x drive cycles. Never had this issue for the multiple years I owned the car prior, and have previously logged data and know the fuel trim was never an issue prior. I followed Subaru's service information diagnostic flow path, that takes you to an ending of "replace PCM". Smoke tested everything, verified fuel pressure, A/F sensor, etc etc etc everything is working 100% as designed. I then started to log some data on it, and noticed my LTFT is consistently -20% indicating the ECU is pulling 20% of fuel out of the map to make lambda. This is the case at idle and through the RPM range anytime you are in closed loop. Then I do some digging into this topic and find that many if not all guys doing this swap are experiencing this. Then I think to my self hmmmmm, I just swapped in an engine with exactly -20% displacement relative to the original motor. So this code makes sense, 20% less displacement should in theory require 20% less fuel to be running stoichiometric. The DTC conditions for setting match the data the ECM is showing me (I believe it was a fuel trim in any direction in excess of 18% - pulling from memory here don't quote me). So I talk to a world renowned tuner who happens to live about an hour from me here in Alberta, Canada (Wester's Garage) and he is telling me sorry there is nothing we can do with the ECM to remap the fuel, it's too old. He suggested using the 2.0L JDM fuel injectors, albiet they are top feed style injectors like the USDM ones, they are of a different size and configuration and 100% not compatible at all. We had tossed the idea around finding an injector that would fit this car that is 20% smaller cc than the original 2.5L injectors. The issue I am finding is that the original 2.5L NA EJ251 motor is about the wimpiest thing Subaru ever produced of the era in theUS market and I am not savvy enough on Subaru interchangeability to know what injector would fit what. I am thinking I will have a very difficult time finding an injector SMALLER that these OEM 2.5L ones in the car currently especially ones that would be a direct swap.
Aside from installing a stand alone fuel management system (ridiculous expense for a wimpy stock car hah), I think that finding an injector of 20% less cc would likely work, as presumably the PWM of the injectors would then match the factory injector (when installed in a 2.5L engine) and I would think the fuel trim would come back into some normality or at least the typical +/- 10% area I would like to see it in where it will not trigger a fuel trim malfunction code.
If anybody has any experience with this swap and any ideas on combatting this, please advise. I had thought about an adjustable fuel pressure regulator (OEM one is vacuum reference and does work properly I did test it) however I don't believe this will help me in all areas (at idle as well as throughout closed loop RPM range). I don't think this will be an accurate enough modification to eliminate this issue. If I could tune the factory ECU I could easily solve this problem, and no the JDM ECU will not work either (much different engine management systems used on JDM motor).
Thanks in advance!
