The VVT swap is a common upgrade for the early Mk1 and Mk2 MX-5s. Allowing you to take advantage of the later 2001-2005 1.8 NBFL VVT Engine, which boasts well for an NA power gain (not so for turbocharging, due to weaker rods when crossing the 230/ft/lbs reported limit). But if a cheap, decent NA gain is your goal, then the 1.8 VVT swap is a sure step in the right direction.
The mechanical engine change is the easy part (the gearbox, starter, mounts etc can all be retained), the stumbling point will always be engine management - should you swap the entire car loom so you can use the VVT ECU? The immobiliser? the smart charge alternator? Or should you keep the stock 1.6/1.8 ECU and somehow retrofit a CAS unit to the engine, as well as lose the VVT benefit? Luckily, there's an easy way to do it, thanks to the ME221 ECU.
Simply install the ME221 that suits your car loom and engine size (normally it would be the 2 plug 8995 unit for the early cars) then a simple mod here and there, a wire run there, and you will retain full VVT control and allow the use of the stock sensors on the newer engine.
The following guide is also in the 8995 Hardware Install guide, but we thought it best to detail it here as a standalone article as well. Enjoy!
Retrofitting an NB/NB2 VVT Engine into an 8995 chassis, using 8995 ME221 and Loom
If you are planning to install an NB or NB2 engine into the NAs engine bay, and keeping the NA wiring (and the 8995 ECU), there are a couple of mods you will need to do - the 8995 ECU fully supports the NB and VVT engine.
In the Engine bay:
- Firstly you will need to wire the Crank and Cam sensors from the NB/NB2 engine into the NA’s CAS sensor connector - this allows you to remove the CAS. Use shielded cable for this.
- You will need to link up the Injectors, TPS and Idle harness to the NA loom - this is simply a case of matching what goes where from the original loom.
- It is recommended to change the alternator to the 89-98 NA (self regulated) type, as that is usually easier than wiring the smart alternator to the ECU - change the alternators pulley to your original V-belt one, and they bolt straight in.
Modifying the ECU:
The ECU requires its pull-up resistors removed, and different ones added externally to support the newer OEM Cam & Crank sensors:
- Remove the ME221 8995 ECU from the car.
- On the underside of the PCB, locate the small resistors marked R6 & R7. You will need to remove these with a soldering iron - be sure to not leave any solder linking the pads.
- You will need 2x 68K resistors (like these).
- Attach one end of each resistor to pin 2K (the 5V supply, shown circled in GREEN)
- Attach the other end of one of the resistors to 2E [CRANK] (ORANGE), and the end of the other to 2G [CAM] (BLUE). (In effect making a 5V pullup of 68K for the CRANK (2E) and CAM (2G) signal lines).
If you want to tackle this yourself, follow the below, but, if you prefer to have us carry out the mod directly on the ECU, we offer this service. Get in touch.
Now ensure you change the settings in the MEITE for the Crank/Cam in the System>Engine Driver to MX-5 NB, and cycle the power. You should then get a steady RPM when cranking, you may need to change your trigger offset angle to approx 642 (or just load "Tuning Data Only" from an NBFL base-map onto your ECU).
To really get the benefits from the new VVT engine, its best to get it working. Supply a 12V ignition switched feed to the VVT solenoids 2 pin plug on one pin, and the other pin, run to the MAC LS2 connection on the ECU. Then, in the IO settings, set MAC LS2 to 'VVT', and your done 🙂
- The connector for the VVT solenoid is a standard 2-pin mini-timer type.
- Run a 12v, ignition switched supply to the VVT solenoid Pin 1 (from the Purge Valve or injector harness is a safe bet), and then run a wire from the VVT solenoid Pin 2 to where the ECU is in the passenger footwell - connect using the MAC/AUX Port guide above to either MAC LS1 or MAC LS2.
- Install an SB340 diode (from RS components) across these two VVT wires - the stripe end of the diode should go the 12v (pin 1) and the other side of the diode to the VVT signal line.
- In the IO Config in MEITE, be sure to set MAC LS1/MAC LS2 to ‘VVT’. You can then tune the VVT control using the settings under the VVT tree item, or simply import the VVT settings and tables from an 0105 VVT basemap.