Setup and wiring notes for the 1989–1995 1.8 MX-5 (NA) running a DigiTune ME221 or ME442 ECU.
Wideband AFR gauge/controller
ME442 ECUs have an inbuilt wideband controller, so they do not require an additional gauge or controller. The ME221 does not have an inbuilt wideband controller, so an external wideband gauge is required. I recommend the AEM X-Series wideband AFR gauge:
AEM X-Series UEGO wideband sensor and gauge
Or an AEM wideband controller without a gauge, if preferred:
AEM X-Series wideband controller
Recommended wiring:
| AEM wire | Connection |
|---|---|
| Red | 12V switched live |
| Black | Chassis |
| White | Red wire with a blue stripe in the OEM narrowband harness |
| Brown | Black wire with a blue stripe in the OEM narrowband harness |
Knock sensor (optional)
The Mk1 MX-5 did not come from the factory with a knock sensor, but one can be retrofitted and connected to the ECU. A knock sensor is recommended for forced-induction or high-compression naturally aspirated engines. Without a knock sensor, I can still tune the car, but I will need to use lower ignition timing in order to guarantee that it will not knock/detonate.
We build and sell knock sensor kits that mount to the Mk2 OEM knock sensor location:
The early Mk1 cars with analogue oil pressure senders need the oil pressure sender spaced out from the block in order to provide room for the knock sensor. This can be achieved with a 1/8″ BSPT extension, or a 1/8″ BSPT to 1/8″ BSPT and 1/8″ NPT T-piece adapter. The use of Teflon (PTFE) tape is recommended when installing oil fittings.