Engine cranks but will not fire: spark, fuel or timing

The starter turns the engine at normal speed. It sounds completely healthy. And nothing happens. That specific symptom is genuinely useful, because it eliminates a whole category of problems before you begin.

If the engine did not crank at all, you would be looking at the battery, starter or immobiliser instead — see car will not start diagnosis.

Combustion needs three things

Air, fuel and spark, delivered at the right moment. A cranking engine is already moving air. So you are down to fuel, spark and timing.

The fastest way to split them is to find out what the engine is trying to do.

Ten minutes with the adapter, before any spanners

Plug in and crank while watching live data. Even on a non-starting engine, the ECU is powered and reporting.

RPM during cranking. Should read 150–300 rpm. If it reads zero while the engine is visibly turning, the crankshaft position sensor is not producing a signal — and that is your answer. The ECU cannot fire injectors or coils without knowing where the crank is. See P0335 crankshaft position sensor.

This single reading resolves a large share of crank-no-start cases in under a minute.

Coolant temperature. A sensor reading a wildly wrong value makes the ECU calculate the wrong starting mixture. A sensor stuck at 90 °C on a freezing morning leaves the engine far too lean to start — see P0113 and P0118.

Fuel rail pressure, where available. No pressure means no fuel, and P0087 covers where it went.

Stored codes. Read them before clearing anything.

The fuel side

Listen for the pump. Ignition on, engine off, in silence. Most cars run the pump for two seconds to prime. No sound at all points at the pump, its relay or its fuse — fuses and relays basics.

Check the obvious. Fuel gauges fail; a tank reading a quarter full can be empty. See fuel gauge reading wrong.

Wrong fuel? If the no-start began immediately after a fill-up, stop cranking. Wrong fuel in the tank needs draining, not more cranking. Similarly, contaminated or waxed fuel — bad fuel quality symptoms.

Smell the plugs. Pull one after several crank attempts. Wet with fuel means fuel is arriving and ignition is the problem. Bone dry means no fuel.

The spark side

Pull a plug and look. Spark plug reading tells you a great deal. Fouled, worn or oil-soaked plugs fail to fire a cold, rich mixture even when everything else is fine.

Crank sensor and cam sensor. Both feed the timing picture. A dead crank sensor gives no start at all; a dead cam sensor often gives a long crank and eventual start as the ECU falls back to a slower synchronisation strategy — P0340 camshaft position sensor.

Immobiliser. Usually shows as a flashing security light and a start-then-immediately-stop. Covered in immobiliser troubleshooting.

The timing side

A jumped timing belt or chain removes the relationship between crank and cam. The engine turns, the valves open at the wrong moment, and it will not fire.

Clues: a rattle before the failure, a stretched-chain code such as P0016, or the fact that it stopped while driving rather than failing to start after a night parked. Related: crankshaft-camshaft correlation P0016 and timing chain vs belt DTC codes.

On an interference engine, a snapped belt means valve damage. Stop cranking immediately. Continued cranking turns a belt job into a cylinder head job.

If the engine cranks noticeably faster and more freely than usual, that is a compression loss across all cylinders — a strong hint that timing has jumped.

Cold weather changes the odds

In winter the same three systems fail for different reasons: thickened oil raising cranking effort, weak batteries, waxed diesel, and marginal plugs that fire warm and not cold. Detail: car not starting in cold and winter starting tips.

Diesel owners should add glow plugs to the list: glow plug diagnostics P0670-P0674.

A sensible order

1. Read live data while cranking — RPM, coolant temperature, rail pressure.
2. Read stored codes.
3. Listen for the fuel pump prime.
4. Pull a plug — wet or dry, and what condition.
5. Check timing if compression feels low or a belt is due.

Working in that order means the two cheapest tests, which need no tools at all, come first.

What not to do

• Do not keep cranking. Ten seconds at a time, then rest. Continuous cranking overheats the starter and, on a flooded engine, washes the bores.
• Do not clear the codes before reading them and their freeze frame.
• Do not add “starting fluid” as a routine measure. On a diesel it can cause serious damage.

After the repair

Confirm it starts reliably cold as well as warm — many faults in this area only show after the car has stood overnight. See P0316 misfire on startup for the related cold-only pattern.

Try it on the free tier of the app — pair an ELM327 adapter and watch RPM while someone cranks. Zero RPM on a turning engine is the single most decisive reading in this entire diagnosis, and it takes one minute.

Read next

• P0230 to P0232: fuel pump primary circuit faults
• P0320 to P0322: ignition and engine speed input circuit
• P0336: crankshaft position sensor range/performance and the reluctor ring