Mazda RX-8 S1 Oil Metering Pump Guide

A full breakdown of the Series 1 RX-8 oil metering pump — how it works, how to diagnose it (including fault codes), how to service it, and the surrounding topics of nozzles, premix and clean oil feed.

The Mazda RX-8 Series 1 Renesis engine uses an Oil Metering Pump, usually shortened to OMP (you’ll also see it called the MOP — metering oil pump — in Mazda documentation), to inject small, controlled amounts of oil into the rotary engine for internal seal and housing lubrication.

This guide covers only the Series 1 RX-8 OMP system. It does not cover the later Series 2/R3 system, which uses a different oil metering arrangement.

The Series 1 system uses a single electronically controlled metering oil pump. The PCM controls the pump through a stepping motor strategy, using engine operating conditions to decide how much oil should be delivered.

Unlike a conventional piston engine, the Renesis has apex seals, side seals and corner seals moving against the rotor housings and side housings. These contact surfaces need a controlled oil film to reduce wear and help maintain sealing — which is why some engine oil consumption is normal on a standard RX-8, and why a healthy OMP matters so much to engine life.

Important: this guide is not a replacement for the Mazda workshop manual. Confirm exact torque values, connector diagrams, part numbers and procedures against the correct service information for your exact model year.

Guide Sections

1. How the OMP Works

The purpose of the OMP, why the rotary engine needs oil injection, and how the Series 1 stepper-motor system delivers oil — from the mechanical drive and plunger stroke control through to the PCM’s initial-set, monitoring and fail-safe functions, plus what’s physically inside the pump.

2. Diagnostics & Testing

Practical checks for diagnosing OMP problems: warning signs, the fault codes (P1684–P1688) and what they actually mean, electrical inspections of the stepper motor and position switch, nozzle and check-valve testing, and line clogging checks — including the common case where the position switch, not the pump, is the real culprit.

3. Removal, Installation & Servicing

How to approach removing, inspecting and reinstalling the Series 1 OMP safely: tools, seals and washers to have on hand, labelling and access, the realistic rebuild-vs-replace decision, and the critical priming and first-start checks afterwards.

4. Oil Nozzles, Premix & Clean Oil Feed

The parts around the pump: how the oil nozzles and their check valves work, testing them, what premixing two-stroke oil does (and doesn’t) achieve, and how clean oil feed conversions like the Sohn adapter change the system — with the trade-offs of each.

Related Pages

• 13B-MSP Engine Running Data — my logged dataset including a reconstructed stock OMP metering map from idle to 9,500 RPM.
• EnduraOMP — my MEng project: a closed-loop electronic replacement for this system.