What follows is a practical, beginner-friendly, step‑by‑step guide to replacing an ignition coil on a Jeep Wrangler (NV3550 indicates the gearbox only — the procedure applies to the engine’s ignition coils, not the gearbox). I explain what every relevant component does, why coils fail and why the repair is needed, how the whole ignition system works (analogy included), how to test coils, and what can go wrong during repair. No fluff — just the facts and clear steps.

Safety first (must read)
- Work on a cold engine. Hot engine parts and spark plugs can burn you.
- Disconnect the negative battery terminal before you touch ignition wiring to avoid accidental sparks or ECM damage.
- Wear eye protection and gloves.
- Avoid open flames or smoking — sparks + fuel vapors = hazard.

Overview — why this repair is needed
- The ignition coil converts the 12 V from your battery into the high voltage (thousands of volts) required to create a spark across a spark plug gap. If a coil fails, the cylinder it feeds will misfire or not fire, causing rough idle, poor acceleration, low fuel economy, engine warning light (check engine light), and sometimes hard starting.
- Typical symptoms: misfire codes (P0300, P0301–P0306), P035x coil-specific codes, rough idle, poor performance, increased fuel consumption, visible arcing, or a smell of unburned fuel.
- Replacing a bad coil restores reliable spark to the cylinder and clears misfires.

How the system works (simple analogy)
- Think of the ignition coil as a step‑up transformer for electricity. Like a bicycle gearing system increases pedal rotations into more wheel rotations, the coil multiplies low-voltage current into high-voltage pulses. The engine computer (ECM) tells the coil when to fire (like the rider tapping the gear shifter), controlling timing and duration. The spark plug is the spark’s outlet — the spark jumps the plug’s gap and ignites the air/fuel charge.

Major components that matter for this job
- Battery: supplies 12 V; powers primary side of coil.
- Ignition coil (or coil pack / coil-on-plug): contains primary winding, secondary winding, iron core, high-voltage terminal or boot. Converts low voltage to high voltage.
- Primary winding: a few turns of thick wire; current flows here under ECM control.
- Secondary winding: many turns of fine wire; generates the high voltage.
- Core: concentrates magnetic field to help induction.
- Housing/insulation: protects windings from heat and oil.
- Boot (on coil-on-plug): rubber/silicone/ceramic piece that seals and conducts high-voltage to plug.
- Spark plug: creates the spark in the combustion chamber. If worn/damaged, it can mimic coil problems.
- Ignition wiring harness and connector: carries signals and battery voltage to coil; ECM triggers coil via a ground or control pulse.
- ECM (engine control module): controls coil firing time and dwell.
- Fuse / ignition relay: supply power to coils; if blown, coils get no power.
- Ground / chassis: necessary return path for current.

Types of ignition setups (know which you have)
- Coil-on-plug (COP): one coil mounted directly on each spark plug. Most modern engines use this.
- Coil pack: one module with multiple coils feeding multiple plugs via short boots/wires.
- Single-coil + distributor (older): one coil feeds multiple cylinders via distributor cap/rotor. (Uncommon on modern Wranglers.)

Before you begin: identify your coil type
- Locate the coils: if each plug has a coil sitting on it — COP. If a single pack mounted somewhere with short wires — coil pack. If you have a distributor cap, procedure differs; consult manual.
- This guide covers coil-on-plug and coil pack style replacement (most common on later Wranglers).

Tools & materials
- Replacement ignition coil(s) — OEM or high-quality aftermarket, matching vehicle year/engine.
- Ratchet and socket set (commonly 8, 10, 13 mm depending on vehicle).
- Extensions and swivel joint (helpful).
- Spark plug socket (if you inspect plugs).
- Torque wrench (recommended for proper bolt torque).
- Flat-blade screwdriver / pick (to release connectors).
- Dielectric grease (for boots).
- Clean rags and small brush.
- Multimeter (for resistance testing) and OBD-II scanner (to read and clear codes).
- Pen/light and small container for bolts.
- Anti-seize for spark plugs only if recommended by manufacturer (use sparingly).
- Shop gloves and eye protection.

Typical resistance values (use as a rough guide only)
- Primary winding: ~0.5–2 ohms (varies by coil).
- Secondary winding: ~5,000–15,000+ ohms (varies widely).
Always compare to the spec in your factory service manual; different coils differ.

Step-by-step replacement (one coil / one cylinder)
Time: ~30–60 minutes for a beginner for one coil; more if you inspect plugs or replace multiple.

1) Preparation
- Park on level ground, set parking brake, engine off and cooled.
- Remove negative battery cable and isolate it (create space so it won’t bounce against terminal).
- If the engine has a plastic cover, remove it (usually held by fasteners or clips).

2) Locate the bad coil
- Use OBD-II scanner and note codes (P030x points to cylinder number, P035x to coil circuit).
- Identify which coil corresponds to the cylinder with the trouble code. On COP systems, coils are on top of each plug and often labeled 1–6. If unsure, consult firing order or a diagram.

3) Unplug coil electrical connector
- Press the connector latch (small tab) and pull straight off. If stuck, gently pry the latch with a flat blade while pulling — avoid pulling on the wires.
- Inspect connector pins for corrosion, bent pins, or melted plastic. Don’t force.

4) Remove coil mounting bolts and remove coil
- Remove the bolt(s) securing the coil (typically a small 8 or 10 mm bolt). Keep bolts in a small container.
- Twist the coil gently while pulling to break the boot seal, then pull straight up to remove. On stuck boots, twist and pull — do not yank the wires.
- Inspect coil boot and inner lip for damage, carbon tracking (black streaks), oil contamination, or cracked/brittle rubber.

5) Inspect spark plug and plug well
- With the coil out you can visually inspect the spark plug boot and plug. If you plan to remove the plug, use the spark plug socket and extension.
- Check plug condition: worn electrodes, heavy carbon, oil fouling indicate other issues but will also cause misfires.
- Clean out debris from plug well before removing the plug to prevent debris falling into the cylinder.

6) Test coil (optional but recommended)
- Primary resistance: connect multimeter leads to the primary pins (the small two pins on the coil connector). Read ohms and compare to spec.
- Secondary resistance: connect one lead to the high-voltage output (where the plug boot connects) and the other to the primary terminal ground (or per manual). Compare to spec.
- Note: On some coils you cannot test the secondary easily without the plug connected; be careful. Also, ECM control circuits can make some tests misleading — scanning codes and swap tests are often more reliable.

7) Install new coil
- If the plug was removed, reinstall spark plug and torque to spec (typical plug torque often 18–25 ft‑lb for many engines — check manual).
- Apply a small amount of dielectric grease inside the boot (thin film at the top of the boot only — keeps moisture out and helps electrical contact). Don’t use too much or get grease on electrodes.
- Seat the new coil straight into the plug well; twist slightly to ensure a good seal.
- Install and torque the coil mounting bolt (snug, usually 7–10 ft‑lb; check factory spec).
- Reconnect the electrical connector until it clicks.

8) Reconnect battery and test
- Reconnect negative battery terminal.
- Clear any stored codes with the OBD-II scanner.
- Start engine. If smooth, let idle and observe. If misfire persists, note codes and proceed to troubleshooting below.

9) Final check and cleanup
- Reinstall engine cover.
- Road test. Monitor for check engine light and performance.
- If problem fixed, you’re done. If not, continue diagnosis.

Quick troubleshooting if misfire continues
- Swap test: swap suspect coil with a known-good coil from another cylinder. If misfire code follows the coil, the coil is bad. If it stays at same cylinder, problem is the plug/wiring/ECM/cylinder mechanical.
- Check spark plugs: worn or fouled plugs can look like a coil problem. Replace plugs if old or out of spec.
- Check wiring/harness and connectors for corrosion, broken wires, or heat damage.
- Check ignition fuse/relay and ECM ground.
- Compression test if misfire persists after coils/plugs are validated — a mechanical issue (low compression, valve issues) can mimic an ignition fault.
- Codes P035x generally indicate coil circuit issues (open/short), check connectors and wiring.

What can go wrong and how to avoid mistakes
- Damaging connector pins: don’t pull on wires. Depress tabs fully and pull straight.
- Breaking the ceramic of the spark plug: use the correct socket and keep the extension straight when removing/installing.
- Cross-threading spark plug: start threads by hand several turns before using wrench, then torque to spec.
- Installing wrong coil or part: match part numbers and connector shape; a wrong coil may fit but not function.
- Leaving debris in plug well: clean before pulling plugs to prevent debris falling into cylinder.
- Not disconnecting battery: can blow fuses or cause sparks; always disconnect.
- Over-tightening coil bolts: strip threads or crack the coil housing. Use a torque wrench or snug carefully to recommended range.
- Oil contamination: valve cover leaks can fill wells with oil causing coil failures. If oil present, replace valve cover gasket and clean boots.
- Reusing brittle boots or damaged coils: replacements are cheap relative to repeat failures—replace boots/coil if any defect.

ECM and code behavior
- After replacing coil, clear codes and test drive. If the coil failure triggered catalytic converter damage (prolonged misfire), additional repairs may be required.
- Intermittent failures may point to heat/thermal issues — coils can crack inside and fail when hot but test fine cold.

When to replace spark plugs too
- If plugs are aged (>30k–60k miles depending on type), fouled, or show abnormal wear, replace them when you replace coils. New plugs plus new coil is best practice.

Torque & spec note
- Exact torque values and resistance specifications vary by engine model/year. Always verify exact specs for your Wrangler engine (2.5L I4, 4.0L I6, etc.) in a factory service manual. The above torque and resistance ranges are typical starting points but not a substitute for the manual.

Final checklist before you finish
- Plugs and coils seated properly and torqued.
- Connectors fully clicked in.
- Battery negative reconnected.
- Codes cleared and engine running smoothly.
- No fluid leaks or debris left in engine bay.

Bottom line
- The ignition coil is the “voltage amplifier” of your ignition system. Symptoms are typically misfire and a check engine lamp. Replacing a coil is a straightforward mechanical job: disconnect battery, unplug coil, remove bolt, swap coil, torque and reconnect, then test. Test coils with a scan tool and/or multimeter, and always inspect/replace spark plugs and boots if suspect. If misfire continues after coil swap testing, move on to wiring, plug, compression, and ECM checks.

You’re set — follow the steps carefully, use the right tools, and consult the factory service manual for torque and resistance specs specific to your Wrangler’s engine.
rteeqp73

jeep shifter issue

NV3550 After 190k...What's inside?? This is the NV3550 transmission out of our 'LS TJ'. We decided to swap it due to the amount of play during shifting and the ...

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