Engine won't start or starts hard: what to check

If the engine cranks but won't start, or starts only after many attempts, the problem is usually one of three things: electrics, fuel delivery, or air. Checking in the right order saves time and parts you don't need.

First: does the engine crank at normal speed?

If cranking is slow and heavy, start with the electrics: a weak battery, corroded or loose terminals, or a tired starter. If cranking is normal and the engine still won't start, the problem is most likely fuel.

Fuel-side causes

• A clogged fuel filter, especially if the fuel comes from an unreliable source.
• Water in the fuel: the water separator is full. Some engines show code SPN 97 (water in fuel).
• Air in the fuel line after a filter change or after running the tank dry.
• A weak lift (transfer) pump.
• The tank is actually empty and the gauge reads wrong. It happens more often than you'd think!

Checks

1. Make sure there is enough fuel in the tank.
2. Drain the water separator from its bottom valve until clean fuel comes out.
3. If the fuel filter is old, replace it, then bleed the air from the line with the hand primer as described in the operator's manual.
4. Check the battery and terminals, clean them and tighten them.
5. If the engine cranks normally, has clean fuel and the problem remains, a technician needs to check the pump and injectors.

Prevention

Change fuel filters on time, drain the water separator regularly, and fill up from trusted stations. Dirty fuel damages the injection pump and injectors, which cost far more than a filter.