Get yourselves a nice tall glass of Long Island and some popcorn, because have I got a woozy.
Background - my K12
It's a JDM K12 March from May 2005. This is a unique K12 as it is an Autech-tuned 12SR, and one of the last three-doors to roll off Nissan Japan's assembly line. Basically, Autech takes a standard 1.2L March off the Nissan factory line, disassembles the engine, and rebuilds it with lightened pistons, rods, rings, heavier-duty bearings, wider-profile intake and exhaust cams, shorter-ratio tranny, and a different ECU which changes fuel mapping, variable timing, and a redline of 7200rpm. This is on top of a redone interior, lower suspension, more chassis reinforcement, body kit, to name a few extras. Basically, an Autech 12SR will push 110HP vs a normal 1.2L's 70HP. Now my car is made a bit more unique as Nismo's Omori Factory has also taken the car, post-Autech, and given it a bespoke tune specific to the Autech engine. This supposedly got it closer to 120HP with just the ECU, a bit more with their complete exhaust system (which I managed to source last year, and installed last week). My understanding is only a few dozen 12SRs ever got the treatment (Nismo only took cars with strict prerequisites such as engine condition, documented history, under a certain mileage etc). Checking the VIN on Nissan's database even greets the local (New Zealand) Nissan dealership with a 'designated special vehicle' message pop-up before you start searching for parts.. And to think I found my car abandoned on a farm as the previous owner didn't want to deal with the oil-burning issue he caused..
Background - what happened
I am the fifth owner in New Zealand. Needless to say, being a hot-hatch the previous four NZ owners (and the one Japanese owner) have thrashed the car. I took it on as a project with no WOF (NZ equivalent to a MOT), no registration. Spent a pretty penny and got it road-worthy in late 2021, and did a slow restore after that while dailying it. Until May 2024, when on a late night heading home whilst driving sensibly, the engine failed. Basically it lost a valve on Cylinder 1 on the motorway - horrible misfire, shuddering, blue smoke etc. Wasn't immediately fatal; managed to limp it home on three cylinders. I sprayed some fogging oil into the cylinders and parked it up. I travel a lot for work - I left NZ in June, and got back in March 2025, where upon return commenced the engine rebuild process.
Engine replacement and rebuild
I did a helluva lot of research while away, scouring English and Japanese forums. I can confirm that between the CR10DE, CR12DE, and CR14DE, the only difference is the block, piston, and ECU. The crank, rods, timing, and the head are exactly same. I've also read of people going from a 1.2L to a 1.4L with the same ECU. But no 'hybrid' rebuilds. And I couldn't find anyone who was brave (or crazy) enough to modify a 12SR engine, more so as parts are long since discontinued by Autech, but here I was. And I wanted to do an OEM-plus rebuild. So basically, get the largest CR engine that Nissan makes (the CR14DE), get all the compatible performance Autech bits out of the broken Autech CR12DE, and put that in the 1.4. Which is exactly what I did. The 1.4L I got was from a K12 with 103k on the clock (from a car that was written off by a rear-side impact). I sourced all other consumable replacement parts straight from Nissan Japan, and basically gave those bits and the 1.4L engine (and my limping car) to a specialist to crack on with the overhaul and install. I would've done it myself, but couldn't justify spending so much on a stand, crane, and lift that I'd only use (hopefully) once.. The 1.4 was pretty much overhauled. Head and block came off for a reskim and new headgasket (might as well as the engine is already out). The new parts sourced also included (and not limited to) the revised (non-stretchy) timing chain, guides, tensioners, water pump, valve cover seals, spark cover seals, exhaust gasket, intake gasket, front-and-rear main seals, thermostat, Autech-specific valve springs (did some horrible things to get these brand new), valve seats, valve seals, and revised dip-stick (reads 3.5L engine oil capacity vs the older 2.9L) etc etc. I got the specialist to reuse the intake and exhaust cams from the old Autech engine (they survived), including any other parts that was not impacted by the 1.2L internally losing a valve, and any good the parts from the 1.4L. The 1.4L was very clean so we had no issues doing so where applicable, though pistons and rings from the 1.2L obviously couldn't be reused in the 1.4L block. And most importantly, I am also reusing the Nismo ECU (ie tuned specifically for the Autech 1.2L motor) for the OEM-plus 1,4L
Situation now
1.4L engine has been rebuilt, installed, and I've been driving it the past week. When cold-starting and driving for the first few minutes, absolute joy. Huge amounts of torque, it will accelerate up a steep hill on 5th gear no sweat. But once it warms up, the power output goes flat. Just no power... That hill aforementioned becomes only doable in third gear (and only just at 4k rpm). The engine revs quickly when cold, but slowly when warm (it will hit 7200rpm eventually). There is no check engine light. The car moves, no smoke, not burning oil, not overheating. I just changed the coolant (from demineralized water to the factory-specified green noting the new headgasket). Engine builder thinks the Nismo ECU is so specific in that, once it starts getting signals from the usual O2 sensor, coolant sensor, MAF etc. it will pull back the fuel trim to 'save the engine from damage'. Basically, Nismo ECU may need to be cleared and retuned for the 1.4L. But noting the value of this car is in the Nismo bits and bobs, this is my absolute last resort.
Hence me here today.
Regardless of my very bespoke situation, I've spent the past few evenings doing research. Reading more forums English and Japanese. I came across one similar situation from someone with a 1.2L K12, and he had a post-cat O2 sensor that was bad. The Japanese K12 models before the first facelift in August 2005 only has one O2 sensor (pre-cat / upstream) - my K12 is from May 2005. I took the installed O2 sensor out, and it seems to have suffered silicone poisoning (I have a used Nismo exhaust manifold and pipe set which I purchased separately last year). So I put in the soot-covered O2 sensor from the old Autech 1.2L. Seems to run at higher performance for a little longer when cold-started, but reverts back to power-loss just the same after a few extra minutes. I just placed an order for a brand new O2 sensor, but I feel this isn't the full fix. Coolant temperature sensor is brand new. Just slapped in a new engine air-filter. Cleaned out the MAF. Throttle body looked clean so untouched. Spark plugs (Nismo NGK heat-range 6) are clean, very slightly whitish brown which indicates good fuel-ratio. Pistons and crank were never removed as part of the skimming process (apparently this is a thing) - cylinder walls have zero scouring after checking today, so I'm happy there. With the engine running absolutely fine when cold (for a few minutes), I know the car is fine. When cold... From the above, I know something is sending the ECU an undesirable reading once it warms up. So either it might be a bad sensor, or the Nismo ECU is just really up tight.
I'm lost as to what other options I can try, bar the ECU reflash. I also have a ECU from a 'normal' 1.4L K12, which I may be more willing to try, though I'm unsure how the BCM will react.
So basically... Anyone have any other suggestions for me to consider / check?
I have tried using generic OBDII readers before but had zero luck (all refuse to communicate with the Nismo ECU). I know my engine builder has an Autel (rather not spend a few thousand on one)... I am hesitant on buying Nisscan and a cable but may do so if push comes to shove. But even before that, before I spend more money blindly, rather keen on picking someone's brain for ideas.
Even before the old 1.2L failed the car was burning oil. I suspect the valve was cracked, and just completely failed in my ownership. Given the amount of damage in the head I'm surprised I managed to keep it going for so long. Right now I am happy I have a daily that isn't a smoke machine and doesn't require an oil top up once a month, but I'd be most keen for something that operates at 100% rather than 50% (if not lower..).
Thank you in advance!
Background - my K12
It's a JDM K12 March from May 2005. This is a unique K12 as it is an Autech-tuned 12SR, and one of the last three-doors to roll off Nissan Japan's assembly line. Basically, Autech takes a standard 1.2L March off the Nissan factory line, disassembles the engine, and rebuilds it with lightened pistons, rods, rings, heavier-duty bearings, wider-profile intake and exhaust cams, shorter-ratio tranny, and a different ECU which changes fuel mapping, variable timing, and a redline of 7200rpm. This is on top of a redone interior, lower suspension, more chassis reinforcement, body kit, to name a few extras. Basically, an Autech 12SR will push 110HP vs a normal 1.2L's 70HP. Now my car is made a bit more unique as Nismo's Omori Factory has also taken the car, post-Autech, and given it a bespoke tune specific to the Autech engine. This supposedly got it closer to 120HP with just the ECU, a bit more with their complete exhaust system (which I managed to source last year, and installed last week). My understanding is only a few dozen 12SRs ever got the treatment (Nismo only took cars with strict prerequisites such as engine condition, documented history, under a certain mileage etc). Checking the VIN on Nissan's database even greets the local (New Zealand) Nissan dealership with a 'designated special vehicle' message pop-up before you start searching for parts.. And to think I found my car abandoned on a farm as the previous owner didn't want to deal with the oil-burning issue he caused..
Background - what happened
I am the fifth owner in New Zealand. Needless to say, being a hot-hatch the previous four NZ owners (and the one Japanese owner) have thrashed the car. I took it on as a project with no WOF (NZ equivalent to a MOT), no registration. Spent a pretty penny and got it road-worthy in late 2021, and did a slow restore after that while dailying it. Until May 2024, when on a late night heading home whilst driving sensibly, the engine failed. Basically it lost a valve on Cylinder 1 on the motorway - horrible misfire, shuddering, blue smoke etc. Wasn't immediately fatal; managed to limp it home on three cylinders. I sprayed some fogging oil into the cylinders and parked it up. I travel a lot for work - I left NZ in June, and got back in March 2025, where upon return commenced the engine rebuild process.
Engine replacement and rebuild
I did a helluva lot of research while away, scouring English and Japanese forums. I can confirm that between the CR10DE, CR12DE, and CR14DE, the only difference is the block, piston, and ECU. The crank, rods, timing, and the head are exactly same. I've also read of people going from a 1.2L to a 1.4L with the same ECU. But no 'hybrid' rebuilds. And I couldn't find anyone who was brave (or crazy) enough to modify a 12SR engine, more so as parts are long since discontinued by Autech, but here I was. And I wanted to do an OEM-plus rebuild. So basically, get the largest CR engine that Nissan makes (the CR14DE), get all the compatible performance Autech bits out of the broken Autech CR12DE, and put that in the 1.4. Which is exactly what I did. The 1.4L I got was from a K12 with 103k on the clock (from a car that was written off by a rear-side impact). I sourced all other consumable replacement parts straight from Nissan Japan, and basically gave those bits and the 1.4L engine (and my limping car) to a specialist to crack on with the overhaul and install. I would've done it myself, but couldn't justify spending so much on a stand, crane, and lift that I'd only use (hopefully) once.. The 1.4 was pretty much overhauled. Head and block came off for a reskim and new headgasket (might as well as the engine is already out). The new parts sourced also included (and not limited to) the revised (non-stretchy) timing chain, guides, tensioners, water pump, valve cover seals, spark cover seals, exhaust gasket, intake gasket, front-and-rear main seals, thermostat, Autech-specific valve springs (did some horrible things to get these brand new), valve seats, valve seals, and revised dip-stick (reads 3.5L engine oil capacity vs the older 2.9L) etc etc. I got the specialist to reuse the intake and exhaust cams from the old Autech engine (they survived), including any other parts that was not impacted by the 1.2L internally losing a valve, and any good the parts from the 1.4L. The 1.4L was very clean so we had no issues doing so where applicable, though pistons and rings from the 1.2L obviously couldn't be reused in the 1.4L block. And most importantly, I am also reusing the Nismo ECU (ie tuned specifically for the Autech 1.2L motor) for the OEM-plus 1,4L
Situation now
1.4L engine has been rebuilt, installed, and I've been driving it the past week. When cold-starting and driving for the first few minutes, absolute joy. Huge amounts of torque, it will accelerate up a steep hill on 5th gear no sweat. But once it warms up, the power output goes flat. Just no power... That hill aforementioned becomes only doable in third gear (and only just at 4k rpm). The engine revs quickly when cold, but slowly when warm (it will hit 7200rpm eventually). There is no check engine light. The car moves, no smoke, not burning oil, not overheating. I just changed the coolant (from demineralized water to the factory-specified green noting the new headgasket). Engine builder thinks the Nismo ECU is so specific in that, once it starts getting signals from the usual O2 sensor, coolant sensor, MAF etc. it will pull back the fuel trim to 'save the engine from damage'. Basically, Nismo ECU may need to be cleared and retuned for the 1.4L. But noting the value of this car is in the Nismo bits and bobs, this is my absolute last resort.
Hence me here today.
Regardless of my very bespoke situation, I've spent the past few evenings doing research. Reading more forums English and Japanese. I came across one similar situation from someone with a 1.2L K12, and he had a post-cat O2 sensor that was bad. The Japanese K12 models before the first facelift in August 2005 only has one O2 sensor (pre-cat / upstream) - my K12 is from May 2005. I took the installed O2 sensor out, and it seems to have suffered silicone poisoning (I have a used Nismo exhaust manifold and pipe set which I purchased separately last year). So I put in the soot-covered O2 sensor from the old Autech 1.2L. Seems to run at higher performance for a little longer when cold-started, but reverts back to power-loss just the same after a few extra minutes. I just placed an order for a brand new O2 sensor, but I feel this isn't the full fix. Coolant temperature sensor is brand new. Just slapped in a new engine air-filter. Cleaned out the MAF. Throttle body looked clean so untouched. Spark plugs (Nismo NGK heat-range 6) are clean, very slightly whitish brown which indicates good fuel-ratio. Pistons and crank were never removed as part of the skimming process (apparently this is a thing) - cylinder walls have zero scouring after checking today, so I'm happy there. With the engine running absolutely fine when cold (for a few minutes), I know the car is fine. When cold... From the above, I know something is sending the ECU an undesirable reading once it warms up. So either it might be a bad sensor, or the Nismo ECU is just really up tight.
I'm lost as to what other options I can try, bar the ECU reflash. I also have a ECU from a 'normal' 1.4L K12, which I may be more willing to try, though I'm unsure how the BCM will react.
So basically... Anyone have any other suggestions for me to consider / check?
I have tried using generic OBDII readers before but had zero luck (all refuse to communicate with the Nismo ECU). I know my engine builder has an Autel (rather not spend a few thousand on one)... I am hesitant on buying Nisscan and a cable but may do so if push comes to shove. But even before that, before I spend more money blindly, rather keen on picking someone's brain for ideas.
Even before the old 1.2L failed the car was burning oil. I suspect the valve was cracked, and just completely failed in my ownership. Given the amount of damage in the head I'm surprised I managed to keep it going for so long. Right now I am happy I have a daily that isn't a smoke machine and doesn't require an oil top up once a month, but I'd be most keen for something that operates at 100% rather than 50% (if not lower..).
Thank you in advance!
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