Quick Check – Ignition System

QC – Intermittent No Spark (Ignition)

Tools: Spark tester, multimeter, 12V test light, jumper lead, basic scan tool (if available).

Safety: Secure loose clothing. Keep hands clear of belts/fan. Use insulated tools when probing ignition circuits.

0) Prove spark loss when the fault occurs

Do not assume ignition just because the engine died. You must catch the failure in the act.

1. Install a spark tester and operate the vehicle. Crank or run the engine until the fault appears.
   Result:
   • Spark remains present: ignition is not the cause. Exit to Fuel or Mechanical QC.
   • Spark disappears: continue.
   
   Proof: QTS – Intermittent Spark Loss Confirmation (coming)

1) Power feed stability under vibration

Most intermittent no-spark faults are power or ground related. Vibration exposes marginal connections.

1. Monitor ignition feed voltage. Back-probe coil or module power with a test light or meter.
2. Wiggle test: While cranking or idling, gently move ignition switch wiring, relay sockets, and fuse block.
   Result:
   • Voltage drops or spark flickers: repair power feed or connector.
   • Voltage remains stable: continue.
   
   Proof: QTS – Ignition Feed Intermittent Drop Test (coming)

2) Primary switching dropout check

Determine whether the coil is losing its trigger or losing its output.

1. Probe coil primary control. Test light from battery positive to coil negative or driver wire.
2. Observe during failure.
   Result:
   • Pulsing stops: trigger loss. Go to Step 3.
   • Pulsing continues: coil/secondary failure. Go to Step 4.
   
   Proof: QTS – Coil Trigger Dropout Test (coming)

3) Trigger loss: sensor and controller checks

If primary switching drops out, the controller is losing position information or shutting down.

1. Watch RPM signal during the event.
   No RPM: crank/cam sensor, wiring, or air gap fault.
2. RPM present but no trigger: ECU or ignition module driver failure.
3. Harness flex test: Move crank/cam sensor wiring and module connectors to provoke the fault.

Proof: QTS – Crank/Cam Signal Intermittent Loss (coming)

4) Coil or secondary intermittent failure

If triggering remains but spark drops out, the failure is downstream.

1. Swap-test the coil. Replace with known-good unit and re-test.
2. Inspect secondary components. Look for cracked housings, carbon tracking, moisture intrusion, or loose boots.
3. Check plug gap. Excessive gap raises voltage demand and exposes marginal coils.

Proof: QTS – Intermittent Coil Failure Confirmation (coming)

5) Ground integrity under load

Ground faults often test good at rest and fail under vibration or current load.

1. Voltage drop test grounds. Measure voltage between module/coil ground and battery negative during run.
   Fail: more than a few tenths of a volt indicates a bad ground path.
2. Inspect ground locations. Engine block, head, firewall, and battery grounds must be clean and tight.

Proof: QTS – Ignition Ground Drop Test (coming)

6) Decision closure

• Spark never drops: ignition ruled out. Route to Fuel or Mechanical QC.
• Ignition feed drops: repair power supply, relay, switch, or connector.
• Primary trigger drops: diagnose crank/cam signal or controller logic.
• Trigger present, spark lost: coil or secondary intermittent failure confirmed.
• Ground drop present: repair ground path.

Next links: Ignition Troubleshooting Hub | QC – Cranks, No Start | QC – Hot No Start | QC – Starts Then Stalls