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Ignition coil inspection

Inspect Mazda MX-5 NB ignition coils systematically to separate true coil failure from plug, wire, connector, or fueling issues.

Difficulty
Intermediate
★★★☆☆
Est. Time
45-90 min
Models
NB1 & NB2
Last Updated
2026-02-26

Before You Start / Safety

  • Work on a cool engine.
  • Keep hands/tools clear of moving belts/fans during running checks.
  • Do not force repeated cranking if you smell fuel strongly; ventilate first.

Warning: “misfire code can be caused by an ignition problem, a fuel problem or a compression problem, so don’t jump to conclusions…” https://www.aa1car.com/library/ignition_coils.htm

Required Tools

  • OBD-II scanner (for NB2 and many NB1 retrofits)
  • Digital multimeter
  • Basic socket set and screwdrivers
  • Insulation-safe light source
  • Contact cleaner (electrical)

Required Parts / Fluids

  • Replacement ignition coil pack (if confirmed faulty)
  • Optional ignition leads/wires if degraded
  • Optional spark plugs if fouled or worn

Model-specific notes (NB1 vs NB2)

  • NB1/NB2 both use coil-based ignition, but wiring/part revisions can differ by year and market.
  • Always confirm exact test specs (if using resistance checks) by year/VIN manual.

Manual-reference quote: “The Manuals are in PDF format. You can use Adobe Reader to read or print them.” https://www.mellens.net/mazda/

Step-by-Step Procedure

1) Confirm the symptom pattern

Log if the issue happens at idle, under load, or only hot. Coil failures often worsen with heat/load, but this is not exclusive.

2) Scan for codes (if available)

Read and note misfire and ignition-related DTCs before clearing anything.

High-risk quote: “On 1996 and newer engines with OBD II… a coil failure will usually set a P030X misfire code… But a misfire code can be caused by an ignition problem, a fuel problem or a compression problem…” https://www.aa1car.com/library/ignition_coils.htm

3) Visual inspection first (engine OFF)

Check coil housing for cracks, carbon tracking, melted spots, and connector looseness/corrosion.

Inspect plug condition, plug gap growth, and lead condition/routing. Bad plugs/leads can overload or imitate coil faults.

High-risk quote: “the number one killer of ignition coils is voltage overload caused by bad spark plugs or plug wires.” https://www.aa1car.com/library/ignition_coils.htm

5) Basic circuit sanity checks

Confirm coil has proper supply and switching signal context before replacement decisions.

High-risk quote: “If a coil has battery voltage at its positive terminal and is being grounded on and off… but is not producing a spark, the coil is defective and needs to be replaced.” https://www.aa1car.com/library/ignition_coils.htm

6) Connector/fuse/loom reality check (NB community practice)

On modified or ECU-updated cars, verify the correct ignition/engine fuse path and loom integrity before blaming the coil itself.

Community quote: “…on the MX5 mk2 there is no fuse titled ‘ignition coil’ fuse so I take it is the ‘Engine’ 15amp fuse…” https://www.mx5nutz.com/threads/ignition-coil-fuse.149694/

7) Decide and repair

  • If coil body is damaged or no-output fault is confirmed with proper feed/trigger, replace coil.
  • If feed/trigger is unstable, repair wiring/connector/ECU-side issue first.
  • If plugs/wires are poor, correct those and re-test before coil replacement.

Community confirmation quote: “…power was on the ignition coils for a bit longer… went for a test drive… it kept loosing power…” https://www.mx5nutz.com/threads/ignition-coil-issue.149944/

Torque Specs / Capacities

  • Coil bracket fastener torque varies by coil bracket style and year.
  • Use the year/VIN workshop specification for final torque values.
  • For related spark-plug removal checks, keep cool-engine handling and proper torque discipline.

High-risk quote: “you should only remove and install spark plugs in a cool engine, because metal expands when hot and thread damage can happen.” https://ngksparkplugs.com/en/resources/spark-plug-installation

Verification / Post-service checks

  • Idle quality stable after warm-up
  • No load misfire under moderate acceleration
  • No new DTCs after one full drive cycle
  • Coil connector remains secure with no intermittent cutout over bumps

Uncertainty / Open Questions

  • Public sources do not provide one single universal NB coil resistance pass/fail value for every market/year revision.
  • Use this guide for fault isolation sequence, then apply exact manual specs for your VIN.

Images

No reusable images were added in this run.

Image Credits

  • No images used.

Sources

  1. Mellens.net — Mazda Miata Factory Service Manuals. Retrieved 2026-02-26. https://www.mellens.net/mazda/
  2. AA1Car (Larry Carley) — How to Diagnose and Test an Ignition Coil. Retrieved 2026-02-26. https://www.aa1car.com/library/ignition_coils.htm
  3. NGK — Spark Plug Installation. Retrieved 2026-02-26. https://ngksparkplugs.com/en/resources/spark-plug-installation
  4. MX5Nutz Forum — Ignition Coil Fuse? Retrieved 2026-02-26. https://www.mx5nutz.com/threads/ignition-coil-fuse.149694/
  5. MX5Nutz Forum — Ignition Coil Issue. Retrieved 2026-02-26. https://www.mx5nutz.com/threads/ignition-coil-issue.149944/