Long Crank Before Start: Evidence-Driven Diagnosis

Symptom-first framework

1. Clarify complaint — long crank cold? hot? after sitting? every start?
2. Confirm operating condition — temperature, time since last run, recent fill
3. Retrieve DTCs — all modules
4. Inspect freeze-frame / live data — conditions when it last occurred
5. Identify affected system — fuel, sensor, battery, timing
6. Form differential — rank by evidence
7. Select decisive test — most changes probability
8. Update hypothesis
9. Confirm cause
10. Repair
11. Verify — start under the condition that failed

Cold vs hot

The temperature at which the long crank occurs is the first split:

• Long crank cold (first start of the day) → fuel-pressure bleed-down overnight, cold-enrichment/coolant-sensor, low crank speed (cold oil drag)
• Long crank hot (after a run, warm soak) → vapour lock, hot sensor failure (crank sensor), pressure bleed-down when hot, hot-start enrichment
• Long crank every start → slow pressure build, weak pump, control-valve, slow crank

Fuel-pressure build

On direct injection, the ECM enables injection at a minimum rail pressure. If pressure builds slowly, the crank is long until the threshold is reached.

• Requested vs actual rail pressure during cranking — actual must rise to the enable threshold quickly
• Slow build → LP supply, HPFP wear, control valve, filter
• See the Fuel Rail Pressure guide and P0087.

Pressure bleed-down

After shutdown, rail pressure should hold. If it bleeds down:

• Injector leak-down — an injector drips fuel into the cylinder, pressure falls
• Check-valve / regulator — fuel flows back to the tank
• HPFP internal leak — pressure bleeds back

A pressure hold test (gauge on the rail, watch after shutdown) confirms bleed-down. The next start is long because the pump rebuilds from zero. This is a classic overnight long-crank cause.

Crank speed

The ECM enables injection at a minimum crank RPM too. A slow crank takes longer to reach it:

• Weak battery — slow crank, low cranking voltage
• Poor ground / terminals — voltage drop slows the starter
• Cold oil drag — higher cranking load cold

A long crank that is actually a slow crank is a battery/ground fault, not fuel. See the Battery Voltage guide.

Engine-speed signal

A marginal crank signal can take several revolutions before the ECM is confident enough to enable injection — a long crank that becomes a no-start when the signal fails fully. Scope the crank sensor. See the Crank Sensor Waveform guide and P0335.

Injector / fuel delivery

• Injector leak-down → pressure bleed (above)
• Slow pressure build → pump/filter/HPFP
• Injector balance — a badly flowing injector delays that cylinder's contribution

Temperature-dependent faults

• Coolant sensor biased cold — over-enrichment, flooding, long crank
• Coolant sensor biased hot — under-enrichment on cold start
• Crank sensor thermal failure — drops out hot, long crank hot then no-start
• Vapour lock (hot soak) — fuel vaporises in the line; long crank until it clears

Immobiliser authorisation

Some immobilisers take longer to authorise with a weak key transponder or a marginal antenna — a long crank that is actually a slow authorisation, not fuel. Check for immobiliser codes.

Compression / timing

• Low compression (cold) — slow to fire
• Timing chain stretch — cam phase shifted, correlation code, long crank. See the Crank/Cam Correlation guide.

Evidence comparison cold vs hot

The decisive technique: compare the same evidence cold vs hot.

• Crank speed (cold vs hot)
• Cranking rail pressure build (cold vs hot)
• Coolant sensor reading vs actual temperature
• Crank signal on a scope (cold vs hot)

The variable that differs between the two conditions points to the cause.

Links

• P0087 / P0191 — rail pressure faults
• Fuel Rail Pressure — requested vs actual
• Cranks But Won't Start — the full no-start framework
• Crank Sensor Waveform — signal integrity

Common mistakes

• Assuming long crank is always a fuel pump
• Not comparing cold vs hot
• Not performing a pressure hold test for bleed-down
• Overlooking slow crank speed (battery/ground)
• Missing coolant-sensor bias
• Not scoping the crank sensor for hot failure