let’s walk through a complete, systematic diagnostic procedure for engine starting problems, written like a mechanic’s checklist. I’ll give you the tests to run, how to run them, expected values, how to interpret results, and next steps. Use this as a step-by-step troubleshooting map to isolate the fault quickly and safely.

Overview — what “starting problems” mean

When you try to start the engine, one of these broad outcomes occurs:

No crank — nothing turns.
Crank but no run — starter turns engine but it doesn’t fire.
Cranks slowly — starter turns sluggishly.
Starts then dies — engine catches briefly or runs then stalls.

Each outcome points to a different set of systems to check (electrical/starter, ignition, fuel, air/compression, or ECU/security).

Safety Measures before diagnosing:

Work in a well-ventilated area when cranking (avoid exhaust buildup).
Wear eye protection and insulated gloves for electrical tests.
Use insulated tools near battery and starter.
If you spray starting fluid, keep flames and hot surfaces away.
Disconnect battery before doing major wiring work.
Refer to the vehicle service manual for exact connector locations and safe test procedures.

Tools you’ll want:

Digital multimeter (DVM) — voltage, continuity, resistance.
Test light or noid light (for injector pulse).
Fuel pressure gauge (with correct adapter).
Compression tester and/or leak-down tester.
Scan tool / OBD-II reader capable of live data and freeze frame.
Clamp ammeter (for starter draw) or a starter load tester.
Spark tester or spare spark plug for spark checks.
Basic hand tools, jumper wires, battery charger/jump pack.

High-level diagnostic flow (do these in order)

Verify symptom & listen/observe
Battery & connections (power source)
Starter & cranking circuit (if no crank)
Fuel system (if cranks but won’t run)
Ignition system & sensors (spark, crank/cam sensors)
Air & mechanical (compression/timing)
ECU/immobilizer/security & DTCs
Advanced tests (oscilloscope, fuel trim, injector waveform)

Step-by-step detailed diagnostics

Step 1: Verify symptom & gather clues

Ask/observe: does it crank? any clicking? lights dim during cranking? check-engine or immobilizer lights on dash? fuel smell?
These clues narrow first checks (e.g., single click → solenoid, rapid clicks → weak battery/connection).

Step 2: Battery & main power distribution (always start here)

Why: everything depends on good battery voltage and low resistance connections.

Tests:

Resting voltage (key off): 12.6–12.7 V = fully charged. <12.4 V = partially discharged.
Voltage while cranking: should not fall under ~10.0 V. If it drops below ~9–10 V and lights go out, battery or cable issues.
Headlight test: turn headlights on, then crank — if headlight brightness collapses heavily, battery or cable/ground problem.
Inspect terminals & ground straps: clean, tight, no corrosion. Pull back cable boot to confirm metal-to-metal contact.
Load test: if available, perform battery load test or use a charger that tests battery health.

Interpretation:

Low resting voltage → charge/replace battery.
Voltage drops badly during crank but battery was good at rest → high internal resistance (battery weak) or poor cable/ground or failing starter drawing excessive current.

Next steps:

Clean/tighten terminals; measure voltage at starter B terminal during crank — if low, trace cable resistance.

Step 3: Starter circuit & starter motor (if no crank or single click)

Inspect: starter solenoid, starter motor, starter relay, ignition switch, neutral/park or clutch interlock, wiring, main fusible links.

Tests:

Listen: single click = solenoid pulls but motor not turning (worn motor or bad brushes). Rapid clicking = battery/cable problem. Silence = no solenoid activation (ignition switch/relay/interlock).
Voltage at solenoid control terminal: turn key to start and measure. You should see battery voltage at the small terminal when key is cranked. If yes but starter doesn’t spin → starter internal fault.
Voltage at starter motor B terminal during crank: should be near battery voltage. If not, heavy cable resistance or blown link.
Tap test: gently tap starter while someone cranks — if it occasionally starts, brushes or commutator issue.
Starter draw test (clamp ammeter): typical draws: small petrol engines ~100–200 A; larger engines higher (200–600 A). Excessive draw (>spec) suggests mechanical drag or shorted armature; very low draw suggests open winding.

Interpretation:

No voltage to solenoid → ignition switch, relay, interlock or wiring issue.
Voltage present but no motor spin → starter motor/solenoid bad.
High starter draw → starter mechanical problem or seized engine (see mechanical checks).

Swap starter relay with identical relay if unsure, bench test starter if necessary, inspect neutral/clutch switches.

Step 4: Fuel system (if engine cranks but won’t start)

Goal: confirm fuel being delivered, pressure and injector operation.

Checks & tests:

Listen for fuel pump prime: turn ignition to ON (not start) — pump should run ~2s prime. No sound → pump/relay/fuse. Some modern cars mute pump with security system—use scan tool to command pump.
Fuel pressure test: connect pressure gauge to Schrader or fuel rail. Typical port fuel injection (low-pressure) specs vary widely — common gasoline systems: ~30–60 psi (check service manual). Diesel and direct injection are different (high pressure) — check manual.
Fuel pressure while cranking: pressure should remain within spec. Rapid drop means pump or check valve issue.
Injector pulse (noid light): backprobe injector connector and verify pulse while cranking. If injectors aren’t pulsing, ECU or crank sensor issue likely.
Starting fluid test (careful): spray small amount into intake; if engine fires briefly → fuel delivery issue. If no effect → likely ignition/compression.

Interpretation:

No pump prime / low pressure: bad pump, relay, fuse, wiring, clogged filter, or empty tank.
Pump runs but no pressure / low pressure under cranking: pump weak or leaking check valve.
Injector pulses but no fuel to cylinder or too lean: injectors clogged or fuel rail problem.

Check pump relay/fuse, fuel pump voltage at tank connector while key ON, inspect ground, check filter and lines.

Step 5: Ignition & spark (if cranks but no start)

Goal: verify spark quality and timing.

Tests:

Spark test: remove a plug, connect to plug wire and ground plug body to engine block; crank and look for blue spark. Use an inline spark tester if available.
Check spark under load: weak, orange spark indicates weak coil or low battery.
Coil primary & secondary resistance: compare to spec in manual (values vary by model). If grossly out of spec, replace coil.
Check coil firing while cranking: use oscilloscope or scan tool to view dwell/pulse signals.
Check ignition control module / distributor (if applicable).

Interpretation:

No spark: possible causes — ignition coil(s), ignition module, crankshaft position sensor, cam position sensor, blown IGN fuse, ECU.
Intermittent spark or weak spark: cracked plug wires, worn plugs, failing coil, bad ground.

If no spark and no cam/crank sensor codes, check for crank sensor signal (see next section), ignition power supply (fuses, relays), and immobilizer.

Step 6: Crankshaft & camshaft position sensors (CKP/CMP)

Why: modern ECUs rely on crank and cam sensors to time injection and ignition. If the ECU doesn’t see crank pulses, it won’t inject or spark.

Tests:

OBD-II scan for P0335 (crank pos) or P0340 (cam pos) codes.
Scope or DVM frequency test: with crank sensor connector unplugged, measure resistance (if passive) or reference voltage (if active). Best practice: use oscilloscope to view signal while cranking — you should see a clean square or sinusoidal waveform depending on sensor type.
Backprobe signal wire while cranking: verify pulses. No pulses → sensor or reluctor wheel damage or wiring fault.

Interpretation:

No crank sensor signal: ECU won’t fire injectors/coils. Replace sensor or repair wiring/reluctor.

Step 7: Air intake & throttle body / MAF / MAP

Why: no air or wrong metering = no start or poor start.

Checks:

Air filter and intake leaks: inspect physically.
MAF sensor: if dirty, engine may not start or will run poorly. Clean carefully with MAF cleaner (do not touch elements).
Throttle position sensor (TPS) and throttle body: a stuck throttle or dirty TB can prevent air flow. Use scan tool to check TPS angle and if throttle plate moves with command (for drive-by-wire).
MAP sensor: check reference pressure and voltage if engine uses MAP.

Interpretation:

Large vacuum leak: can cause runaway idle or failure to start if severe.
MAF failure: no start or hard start often with codes.

Step 8: Compression & mechanical checks (if spark/fuel ok but no start or weak start)

Why: engine requires adequate compression to ignite the mixture.

Tests:

Compression test: warm engine (per manual), disable fuel/injection or ignition so it won’t start, crank at consistent speed (use starter). Typical gasoline engines: 100–200 psi per cylinder; values should be similar across cylinders (within ~10–15% or 10–20 psi). Diesel engines have much higher compression (300–500+ psi). Check manufacturer spec.
Leak-down test: more diagnostic — pressurize each cylinder and measure % leakage. >20% leakage indicates valve/piston/ring problem.
Timing belt/chain check: if timing belt/chain broken or slipped, valves/pistons not synchronized — low/no compression.

Interpretation:

Low compression on one or more cylinders: valve issues, head gasket failure, worn rings, broken timing.
All cylinders low: timing belt/chain failure or catastrophic mechanical problem.

Step 9: ECU, security/immobilizer & sensor fuses/relays

Why: if ECU disabled or immobilizer activated, it can cut fuel or spark.

Checks:

Scan for codes and ECU communication: does the scanner communicate? If not, check ECU power/grounds/fuses.
Immobilizer indicators: flashing key symbol or immobilizer light commonly indicates key transponder not recognized. Try spare key.
Main fuses and EFI relay check: inspect/replace if suspect.

Interpretation:

No ECU communication: bad ECU, main power, or CAN bus fault.
Immobilizer active: resolve with correct key or dealer reprogramming.

Step 10: Other advanced / situational tests

A. Fuel trim and OBD live data

Use a scan tool and watch long/short term fuel trims, sensor values, and injector pulsewidth while cranking or during start attempt.
Erratic or extreme values point to sensor or fueling issues.

B. Injector waveform & balance testing

Use oscilloscope to view injector drive waveform for misfires or weak pulses.
Perform flow/balance test if you suspect clogged injectors.

C. Oscilloscope checks

Oscilloscope is gold standard for crank/cam sensor waveforms, coil secondary patterns, injector drivers, and starter motor battery current waveform.

D. Crankcase & vacuum leak smoke test

Introduce smoke to intake/PCV system to find leaks invisible to eye.

Typical diagnostic decision table

No crank & no dash lights → main battery/connection, fusible link, main relay.
No crank & dash lights ok; single click → starter solenoid or starter motor.
Rapid clicking while cranking → battery voltage collapse or poor connection.
Cranks normally but no start; starting fluid makes it fire → fuel delivery problem.
Cranks normally but no start; starting fluid no effect → ignition or compression problem (spark/CKP).
Intermittent start or stalls after start → security/immobilizer, crank sensor, fuel pump relay, vapor lock, or fuel pressure issues.

Typical numeric thresholds & specs

Resting battery voltage: 12.6–12.7 V.
Voltage during cranking: not less than ~10.0 V (if lower, suspect battery or heavy resistance).
Typical petrol fuel rail pressure (port injection): ~30–60 psi (varies by engine). Check service manual.
Compression (gasoline): ~100–200 psi per cylinder; variation between cylinders should be small.
Starter current draw (typical): small engines 100–200 A, larger up to 600–800 A for diesels. Compare to vehicle spec.
Injector pulse: verify pulsewidth in ms on scanner.

(Always confirm exact values in the vehicle service manual — these are general ranges.)

Final troubleshooting checklist (printable)

Check battery voltage & health. Clean/tighten terminals.

Verify starter operation: listen, test voltage at starter during crank, test starter draw.

Check fuses & relays (starter, EFI/main).

Check interlocks: neutral/park, clutch pedal switch.

Listen for fuel pump prime; test fuel pressure at rail.

Test for spark at plugs; check coil power and control signals.

Scan ECU for DTCs and live data (crank/cam sensors, fuel trims).

Compression test and timing check if mechanical fault suspected.

Inspect immobilizer/key recognition and ECU power/grounds.

If unresolved, use oscilloscope & injector flow tests, or take vehicle to a specialist.