Spark Gate (Coil Output First)

Matches Hub: Step 2 Tools: spark tester, insulated pliers

Goal: Make the spark gate a 2-minute proof, not a debate.

1. Disable fuel.
   Pull fuel pump relay/fuse or disable injectors so you can crank safely.
2. Test spark at the coil output (not the plug first).
   Use a spark tester on the coil tower/coil wire and crank.
   Spark present at coil = prove delivery (QT 5).
   No spark at coil = prove power/trigger (QT 2-4).
   Proof: Ignition Coil Test
   Theory (optional): Spark Energy vs Spark Voltage | Primary vs Secondary Ignition Circuits
3. If spark is weak or intermittent, do not guess.
   Go straight to coil power during crank (QT 2).
   Proof: Ignition Coil Power Feed

Decision: Spark at coil = QT 5. No spark at coil = QT 2.

Coil Power During Crank

Matches Hub: Step 3 and Step 6 Tools: test light, multimeter (optional)

Goal: Prove the coil has real power while cranking, not just key-on power.

1. Prove ignition switch output (source-side).
   Do not assume the switch is good because accessories work.
   Proof: Ignition Switch Pinout
   Deep dive: Ignition Switch and Run/Crank Voltage Drops
2. Probe coil + feed key-on.
   Test light to ground, probe coil power feed.
   Light ON = key-on feed exists. Now prove it holds during crank.
   Proof: Ignition Coil Power Feed
3. Probe coil + feed while cranking (the real test).
   Leave the test light on and crank.
   If it drops out during crank, stop. That is the failure. Repair the feed path before blaming coil/module.
   Proof: Ignition Switch Voltage Drop
   Deep dive: Ignition System Voltage Sensitivity | Grounding in Ignition Systems
4. If power is low, fix the feed path before replacing parts.
   Most weak-spark issues are wiring, grounds, connectors, and switch voltage loss.
   Wiring basics: Wiring 101 – Ignition Power & Ground

Decision: Coil feed holds during crank = QT 3. Coil feed drops out = repair feed path, then re-run QT 1.

Deeper QTS: QTS: Ignition Coil Power Feed | QTS: Ignition Switch Voltage Drop

Trigger Proof (Module/ICM Switching Check)

Matches Hub: Step 3 Tools: test light, multimeter

Goal: Prove whether the module/driver is switching the coil.

1. Confirm coil power is present during crank first.
   If QT 2 fails, fix that first.
2. Run the module switching / signal check.
   This is your “is the brain talking to the coil?” gate.
   If the module never gets a valid trigger, it cannot fire the coil.
   Proof (example: Ford TFI): TFI Module Signal Check
   Deep dive: Magnetic vs Hall-Effect Sensors
3. If switching is missing, do not buy a coil.
   Prove the pickup/sensor signal next (QT 4).
   Proof (example: Ford PIP): Distributor PIP

Decision: Switching present = QT 5 (delivery) and QT 7 (timing). Switching absent = QT 4.

Deeper QTS: QTS: Module/ICM Signal Check (example: TFI)

Pickup Proof (Distributor/Crank Sensor Signal)

Matches Hub: Step 3 and Step 5 Tools: multimeter, test light

Goal: Prove the pickup signal exists. No pickup signal means no spark.

1. If you have no spark at coil, pickup signal is a top suspect.
   Especially on random stall or heat failures.
2. Run the pickup signal test.
   Pickup FAIL = sensor/pickup failure or wiring fault.
   Pickup PASS but still no spark = module/driver or harness issue.
   Proof (example: Ford PIP): Distributor PIP
   Deep dive: Crank Trigger vs Distributor Trigger

Decision: Pickup FAIL = repair/replace sensor/pickup or wiring, then re-run QT 1. Pickup PASS = return to QT 3 and re-check module/driver path.

Deeper QTS: QTS: Pickup Proof (example: Distributor PIP)

Spark Delivery (Cap, Rotor, Wires)

Matches Hub: Step 4 Tools: spark tester, flashlight

Goal: If the coil is firing, prove whether that spark is actually getting to the plugs.

1. Confirm spark at the coil output first.
   If coil spark is dead, go back to QT 2-4.
2. Inspect cap and rotor (if equipped).
   Carbon tracking, corrosion, cracked towers, burned rotor tip.
   Coil spark good but plug spark missing usually lives right here.
3. Verify wire routing and continuity.
   One crossed pair can mimic fuel issues all day long.
4. Re-test spark at multiple plug wires.
   Do not test one cylinder and call it done.

Decision: Delivery FAIL = repair cap/rotor/wires/plugs and re-run QT 1. Delivery PASS but still misfires = QT 7 (timing) then QT 8 (mechanical sync).

Deep dive: Suppression vs Solid-Core Plug Wires | Resistor vs Non-Resistor Spark Plugs | Spark Plug Gap vs Cylinder Pressure | Spark Plug Heat Range

Ignition Switch Voltage Drop

Matches Hub: Step 6 Tools: multimeter

Goal: Catch the “it has power, but not enough power” problem.

1. Measure voltage at coil feed while cranking.
   Key-on numbers are not the story. Cranking is the story.
2. Run the ignition switch voltage drop test.
   If the switch/connectors are dropping voltage under load, you get weak spark, hot failures, and random no-starts.
   Proof: Ignition Switch Voltage Drop
   Deep dive: Ignition Switch and Run/Crank Voltage Drops | Ignition System Voltage Sensitivity
3. If voltage drop is real, fix wiring before parts.
   Wiring basics: Wiring 101 – Ignition Power & Ground

Decision: Excessive drop = repair switch/connectors/feeds, then re-run QT 1. Drop OK but still weak spark = QT 5, then QT 7.

Deeper QTS: QTS: Ignition Switch Voltage Drop

Base Timing Proof (Distributor Setup)

Matches Hub: Step 7 (and prevents false fuel chasing) Tools: timing light

Goal: Prove spark is happening at the right time.

1. Only do this after coil spark is proven.
   If QT 1 fails, timing checks are a distraction.
2. Verify base timing and distributor setup.
   If it is stabbed wrong, it will act like fuel problems all day long.
   Proof: Base Timing Distributor Setup
   Deep dive: Base Timing vs ECU-Controlled Timing

Decision: Timing incorrect = correct setup, then re-run QT 1. Timing correct but symptoms persist = QT 8.

Mechanical Sync (Timing Chain)

Matches Hub: Step 5 and Step 7 Tools: basic hand tools, eyes

Goal: Catch a mechanical timing failure that makes ignition look guilty.

1. Watch for classic signs.
   Backfire through intake, lazy cranking, sudden “ran yesterday” failure, unstable timing mark behavior.
2. Inspect timing chain condition and slack.
   If the chain jumped or is sloppy, you can chase spark forever and never win.
   Proof: Timing Chain Inspection
   Deep dive: Timing Scatter and Its Causes

Decision: Mechanical sync FAIL = repair mechanical timing, then re-run QT 1 and QT 7. Mechanical sync PASS = return to the Hub and follow the symptom path (Step 5/Step 7).