Adele reached out to ATS about getting the engine rebuilt in her beloved 1986 MR2, which she has owned since 1988! Unfortunately the 4AGE rarely lives past 150k miles, and hers finally expired last year. The 4A has been out of production for 35 years. Rebuilding one of these properly gets complicated and expensive fast, especially since everything bolted to it is also 40 years old. I encouraged her to instead consider a swap, and we could retain the automatic transmission. This would also save many months, as engine builds have to wait on parts, then machining, then assembly. The completed price was about the same for the swap as it would have been for a rebuild, and the car now has a much newer, more reliable, and more powerful powertrain.
For the most part the swap is the same as our normal 2ZR swap. The new Denso compressor has the AC blowing ice cold. She opted for the cruise control option. This is something we’ve been offering for the SW20 2GR swaps for a while, but I hadn’t done a Mk1 yet. This cruise control system is way different than any other Toyota I’ve worked with. With some creative connection, CANbus decoding, and code writing, I have the cruise working completely like factory. These modern engines have drive by wire with cruise control built into the ECU, you just have to activate it. We have a module that reads the signals from the MR2, and converts it into the signals the new ECU needs. It also handles AC idle up, and even turns off the AC compressor at higher throttle positions.
Acceleration and cruise control operation video.
The gains on the dyno were significant. The transmission seems to be about a 16% reduction in power delivery on both the 4A and 2ZR. 4A delivers 95 horsepower to the wheels manual and 80 auto. The 2ZRFE normally makes 130, this one made 108. It’s not a rocket now, but that’s still a very noticeable 35% increase in power delivery.
Read more on the 2ZR swap here.
The Scion xD ECU we use for the swap will control an automatic transmission, so we just needed to install the appropriate transmission. I chose to use a U341E like the ECU expects, from a 09-13 Corolla. If I were to do it again, I would use an 04-06 Scion xB U340E. The Corolla option was more expensive and had some complications.
The front and rear transmission mount on both the Corolla and the xB are the same as a manual 2ZR swap - reuse stock brackets and slot some holes in the mounts. The Corolla option does additionally need the lower hole on the rear mount bracket slotted, the xB does not. The normal Hux Racing passenger side motor mount was used. The top mount is different than any factory mount. For this, I scanned a manual transmission with the mount installed, and scanned the automatic transmission without a mount. I aligned these 2 scans in CAD, and placed the important features in space. I then sent this file to Hux Racing. Eric printed a fixture and welded up a mount with a rubber bushing.
The xD/Corolla U341E transmission uses SW20 S54 axles. The Scion xB U340E uses AW11 C52 axles. I’m pretty sure the AW11 automatic axles are different.
Our transmission came without a dipstick or tube. I actually ended up buying a second transmission just for the dipstick, because I couldn’t find one used. I then grabbed the crucial measurements and 3D printed a new dipstick in ASA.
The U341E only came in cars with ABS standard. I overlooked this. The pattern I’ve observed is that, if a Toyota transmission never came in a car without ABS, they likely didn’t bother putting a speedometer drive gear on the differential. The U341E did not have a gear on the differential. The U340E was used in Toyota Echos without ABS, and therefore has a drive gear for a speed sensor. Luckily, the bellhousing is really easy to remove from these transmissions, and the part that fits is the same as an S54, so we had one laying around. This was a relief. Once that was installed, the MR2 speedometer drive unit installed into the transmission and meshes properly.
The shift selector on the new transmission swung in the opposite direction. We moved over the arm from the MR2 and made a braket for the cable off the front engine mount. The spacing between gears is perfect, it’s just like a stock car.
Wiring was simple. I started with an automatic xD harness. An automatic 09-10 Corolla harness will work just the same for Mk1b applications. The main differences from a manual 2ZR swap were the reverse switch and neutral safety switch. The O/D off switch sends ground and the ECU expects 12v, so there is an additional relay for that.
Well, wiring would have been simple. When we got the car running, there was a code for the converter lock solenoid. Long story short, the 2011+ U341E has slightly different wiring on this circuit. I use 09 xD ECUs and reference an 09 xD wiring diagram. The later model harness has the SL wire on a different pin. Additionally, the later transmissions have the lock solenoid externally grounded, whereas the earlier transmissions have it grounded to the transmission. Early harnesses don’t have this wire at all and it will need to be added to the transmission plug. Late harnesses just need the wire grounded, as it is not grounded when plugged into an early ECU. For simple wiring, make sure you start with an 08-10 harness and use an 09-10 transmission. The xB U340E is also internally grounded, so should work with the 08-10 electronics. However, the gear position switch is different on the U340E. To use this with a 2ZR harness, the plug or switch will need to be swapped. Let it be known, we have not tried the U340E yet, but we do have one here now. I’d bet it will work, and may install one in a spare shell in the future.
We looped the transmission cooler lines, and monitored temperatures for a while. The highest I ever saw, after a while on the dyno with no airlflow was 190F, so I don't suspect that trans temps will be a problem. This is a really light car with very little load at cruising. The cooler lines could be hooked up to the stock cooler on an auto MR2, but the hose routing would be a mess, plus the one on the car was cracked and leaking.
I managed to identify the shift point tables in the tune and made a shift schedule that aligns with how I enjoy driving my manual 2ZR MR2. I really enjoy driving this car. If my wife ever shows interest in having her own MR2 I will likely be repeating this build.
Feel free to reach out if you have any questions!
