Goal: Diagnose and replace faulty ignition coil(s) on a Mitsubishi Delica L300 in plain, beginner-mechanic terms — what each part is, how the ignition system works, why coils fail, how to test and replace them, and what can go wrong.

Safety first
- Work on a cold engine. Hot engines and hot exhaust parts cause burns.
- Disconnect the negative battery terminal before touching electrical parts.
- High voltage risk: coils create thousands of volts. Don’t crank the engine with exposed spark plug boots or with bare hands on the coil output while ignition is on.
- Wear gloves and eye protection.

What an ignition coil is — analogy and core theory
- Simple analogy: an ignition coil is a step-up transformer and a spring-loaded water pump. The battery feeds a lot of low-voltage “water” into the coil’s primary winding slowly; when the current is cut off, that stored energy is rapidly released as a high-voltage “jet” through the coil’s secondary winding to the spark plug. That jet leaps the gap at the spark plug and ignites the air-fuel mix.
- Internally there are two windings: primary (few turns of heavy wire) and secondary (many turns of fine wire) wrapped around an iron core. The primary current builds a magnetic field; when the current is switched off, the collapsing field induces a high voltage in the secondary winding.
- The coil housing contains the windings, core, insulation, and usually an integrated boot that connects to the spark plug (coil-on-plug or coil pack style). A connector on the coil receives a switched primary supply and a control signal (from the ECU or igniter).

Relevant components you’ll see on a Delica L300 (and what they do)
- Ignition coil(s): either coil-on-plug (one coil sits on each spark plug) or a coil pack with multiple outputs and HT leads — depends on engine year and model. They convert 12 V into thousands of volts for the spark.
- Spark plugs: final conductor that creates the spark at the gap in the combustion chamber. Worn plugs increase coil load and cause misfires.
- High-tension (HT) leads / boots: insulated lines or rubber boots that carry the high-voltage from coil to plug (if not COP). Cracks or carbon tracking cause misfires.
- Ignition control module / igniter (or ECU ignition drivers): electronics that switch the coil primary on/off at the right time based on crank/cam sensor signals.
- Crankshaft position sensor (CKP) / cam position sensor: tell the ECU engine speed/position. If they fail, coils may not fire or will fire at wrong time.
- Battery and charging system: supply steady 12 V. Low battery voltage or alternator problems can change coil performance.
- Wiring harness and connectors: supply power and the pulse signal to each coil. Corrosion or broken wires can kill a coil circuit.
- Spark plug wells, gaskets, and mounting bolts: mechanical parts that keep boots sealed and coils mounted.

Why you might repair/replace coils
- Symptoms that point to bad coil(s): rough idle, engine misfire(s), loss of power, poor fuel economy, difficulty starting, check engine light with misfire codes P0300–P0306 or coil-specific P035x codes, visible arcing, or a coil that looks physically cracked/burned.
- Coils can fail electrically (short in windings), thermally (heat cracks insulation), mechanically (cracked housing or boot), or due to connector/wiring faults.

How the system works in operation (step-by-step)
1. ECU reads crank/cam sensors to know cylinder position.
2. At the correct time, ECU/igniter allows current to flow through the coil’s primary winding (battery + via power circuit).
3. Current flowing creates a magnetic field in the core.
4. When ECU/igniter cuts primary current, the magnetic field collapses rapidly.
5. That rapid collapse induces a high voltage in the secondary winding (several thousand to tens of thousands of volts).
6. The high voltage travels through the coil’s output boot or HT lead to the spark plug.
7. The spark plug’s electrodes allow the high voltage to jump the gap and ignite the mixture.
8. The ECU may monitor the current or voltage for diagnostics; it logs misfires if sparking fails.

Tools and parts you’ll need
- Replacement coil(s) — OEM or quality aftermarket. Replace the failed unit(s); with mileage/age, consider replacing all coils in a bank.
- New spark plug(s) if old/worn (good practice when replacing coils).
- Basic hand tools: ratchet, socket set, spark plug socket, extension, screwdriver(s), pliers, torque wrench (recommended), dielectric grease.
- Multimeter (for resistance checks and connector voltage checks).
- OBD-II scanner to read/clear codes.
- Spark tester (if you must visually verify spark; use with care).
- Clean rags, small brush for connector cleaning.

Diagnosis — how to confirm coil failure
1. Read codes first with OBD-II scanner. P035x indicates coil circuit fault; P030x shows a misfire on a specific cylinder.
2. Swap test: swap the suspect coil with a known-good coil from another cylinder. If the misfire or code follows the coil to the new cylinder, coil is bad.
3. Visual inspection: cracked housing, burned boots, oil contamination, carbon tracks (black fine lines) on boot or plug indicate failure.
4. Resistance check (general guidance only — always confirm factory specs):
- Primary winding resistance (two small terminals): usually low, often 0.3–2 ohms.
- Secondary winding resistance (between the output terminal and a primary terminal or ground): often several thousand ohms (1k–20kΩ depending on coil type).
- If readings are wildly out of expected range or infinite, coil is bad.
5. Voltage/pulse check: use a multimeter or oscilloscope to see the primary circuit is getting battery power and switching pulses from the ECU.
6. Spark test: use an inline spark tester to see if the coil produces a spark while cranking — be cautious and follow safety steps.

Step-by-step replacement (coil-on-plug style; adapt if your Delica has coil packs)
1. Preparation
- Park on level ground, set parking brake, engine cold.
- Disconnect negative battery terminal.
- Remove engine cover if present (usually 2–4 bolts or clips).
2. Locate coils
- You'll see coils on top of the engine above each spark plug on a COP setup. On some older L300s you might have a single coil with HT leads to a distributor or coil pack under a cover; replace similarly after removing cover.
3. Remove connector
- Depress the locking tab and gently pull the electrical connector off the coil. Do not yank the wires.
4. Unbolt coil
- Remove the mounting bolt(s) holding the coil down (usually small 8–10mm bolts). Keep track of bolts and any spacers.
5. Remove coil
- Pull the coil straight up. If it’s stuck, wiggle gently to break the seal but avoid prying on plastic.
6. Inspect spark plug and boot
- Pull the spark plug (use a spark plug socket). Inspect electrode and gap, carbon deposits, oil fouling. Replace plug if necessary. Check plug gap per spec.
7. Install new coil
- If coil has a boot, put a small dab of dielectric grease inside the boot (not on the electrode) to improve electrical contact and prevent moisture. Seat the coil firmly over the plug.
- Reinstall mounting bolt and tighten to snug — use torque wrench to manufacturer spec if available.
8. Reconnect electrical connector
- Snap the connector back onto the coil until it locks.
9. Repeat for other coils if replacing more than one.
10. Reconnect battery negative terminal.
11. Clear any stored codes with scanner.
12. Start engine and verify smooth idle, no misfires, and no check engine light. Road test.

Good practices and tips
- Replace spark plugs when replacing a coil if plugs are old/worn — worn plugs increase coil stress.
- Replace all coils if multiple are showing age-related failure; one failing coil often means others are near end-of-life.
- Keep connectors dry/clean. Use contact cleaner and ensure clips lock.
- Never use metal tools near the coil output when engine is cranking.
- Tighten coils to spec to avoid damaging threads or creating poor grounding.

What can go wrong — failure modes and secondary issues
- Internal short or open: coil windings fail; no high voltage produced.
- Cracked boot/housing: allows arcing to engine block or carbon tracking, causing misfires.
- Heat soak: coils run hot and fail intermittently when hot; symptoms may appear only after driving.
- Oil contamination: leaking valve-cover gaskets can soak coils/boots and cause failure.
- Bad spark plugs: high resistance or wrong gap over-stresses coil and shortens life.
- Wiring/connectors: corroded terminals, broken wires, or a weak power supply (blown fuse or relay) can look like coil failure.
- Ignition driver/ECU or crank sensor failure: coils may not fire even if they are good; misdiagnosing will lead to replacing good coils unnecessarily.
- Installation errors: over-torquing bolts, applying grease to wrong surfaces, or not seating coil boots properly cause misfires.

Quick troubleshooting flow
- Read codes → visually inspect → swap coils to see if misfire follows → measure primary/secondary resistances → check supply voltage/pulse to coil → replace coil (and plug) if failure confirmed → re-check codes and running condition.

Final notes for a Delica L300 owner/mechanic
- Confirm whether your exact Delica L300 engine is coil-on-plug or uses a coil pack/distributor before buying parts. Parts numbers vary by engine variant and year.
- Replace coils with correct OEM or high-quality aftermarket parts.
- If replacing coils doesn't cure misfires, continue diagnosing fuel, compression, sensors (CKP), and wiring.

That’s the complete practical and theory guide for ignition coils on a Delica L300. Follow the safety steps, use the diagnostic flow, and replace faulty coils and worn spark plugs together for best results.
rteeqp73

Crash Test 2006 - Present Mitsubishi L 300 / Express Crash Test 2006 - Present Mitsubishi L 300 / Express.

Mitsubishi Delica L300 Starwagon electrical issue FIX (no headlights/tail lights/interior/horn) The 1992 Delica had an ongoing electrical issue, where when hitting an abrupt bump in the road the lights and stereo world cut ...

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