Mazda RX-8 S1 Oil Metering Pump Guide
A practical guide to the Series 1 RX-8 oil metering pump: how it works, how to diagnose it, how to remove and refit it, and the nozzles, premix and clean-oil feed around it.
The Series 1 RX-8 meters small, controlled amounts of oil into the engine to lubricate the seals and housings. Mazda’s manual calls the part the metering oil pump; I use OMP.
This guide covers the Series 1 system only. The Series 2/R3 system is reported to have three nozzles per rotor and a different pump with its own codes, and an electric replacement is a different system again. Mazda’s figures are quoted with a link; owner reports are marked. Confirm connector diagrams and part numbers for your model year.
The guide
- How the OMP works: the pump, stepper, start-up sequence and control logic.
- Diagnostics and testing: fault codes, symptoms and tests.
- Removal, installation and servicing: taking the pump off, refitting it and what to replace.
- Nozzles, premix and clean oil feed: nozzle checks, and what premix or a separate oil supply changes.
- OMP Lab: an interactive model of the start-up checks, faults and commanded step.
The system at a glance
| Pump | Engine-driven pumping, with a stepper motor that sets the stroke |
| Oil nozzles | Two per rotor, tilted towards the side housing |
| Control | The PCM commands the stepper in steps and re-establishes zero at every start by reversing 60 steps |
| Feedback | One on/off position switch; no continuous position sensor |
| If it faults | Fail-safe: stepper fixed at step 7, engine restricted |
| Fault codes | P1686, P1687, P1688 |
Technical review: