Separate the problem into two cases first: does the engine crank at normal speed, or does it crank slowly or not at all? Slow or no cranking is electrical or a safety interlock. Fast, normal cranking with no start is fuel, air or compression.
What you will notice
| Symptom | What it usually points to |
|---|---|
| Starter turns slowly or not at all | Battery, starter, cables or an interlock. Not a fuel problem. |
| Cranks normally, will not fire | Fuel supply, air in the fuel system, shutdown solenoid, or low compression. |
| Fires briefly then dies | Air in the fuel system, or a shutdown or immobilizer circuit cutting fuel. |
| Fires and runs roughly, then stops | Fuel starvation, contaminated fuel, or a fuel filter restriction. |
| No sound at all when the key is turned | Safety lock, battery isolator, neutral or safety circuit, or the key switch itself. |
| Cranks and fires when cold, refuses when hot | Fuel system or injectors — a hot no-start is a specific and telling pattern. |
Most likely causes
| Cause | How to confirm it |
|---|---|
| Battery condition, terminals and cables | The most common cause of slow or no cranking, and the cheapest to rule out. |
| Safety lock lever or seat switch | The machine does not permit starting. Always check the interlocks before opening the fuel system. |
| Air in the fuel system after filter or line service | A very common cause after maintenance, and one that often gets misdiagnosed as a pump failure. |
| Blocked fuel filters or water separator | Fuel starvation producing cranking with no firing. |
| Fuel shutdown solenoid not energizing | The engine cranks but receives no fuel. |
| Immobilizer or anti-theft system | Faults that prevent fuel or crank authorization, sometimes without an obvious warning. |
| Low compression | Rings, valves or head gasket. Cranking speed sounds even but the engine will not fire. |
| Glow plug system failure on cold mornings | Hard cold starting with normal warm starting. |
How to confirm it
- Assess the crank before touching anything
Listen and observe: fast and even cranking means the electrical system is delivering. Slow or uneven cranking means the fault is electrical or mechanical before it is a fuel fault. This observation decides every subsequent step.
- Check battery, terminals and cables
Measure battery voltage at rest and while cranking. A battery that reads well at rest and collapses under cranking load is the single most common and cheapest explanation. Inspect and clean terminals; a surprising number of no-starts are cable resistance.
- Verify the interlocks
Safety lock lever, seat switch, battery isolator and any neutral requirement. A machine that will not crank at all frequently has one of these engaged or failed, and nothing in the fuel system is involved.
- Check for air in the fuel system
Bleed the system at the filter and at the pump. If the engine starts and then dies, or needs bleeding repeatedly, air is entering somewhere — typically a filter housing seal or a cracked suction line.
- Confirm fuel is reaching the injection system
Crack a delivery line or check feed pressure depending on the system. Establishing whether fuel arrives at the pump separates a supply fault from a pump or injector fault.
- Check the shutdown solenoid and immobilizer
Confirm the shutdown solenoid energizes when the key is turned, and that no immobilizer or anti-theft condition is present. These fail in ways that mimic a fuel fault exactly.
- Measure compression if fuel and electrical are correct
Even cranking with fuel present and no firing points to compression. A compression test or blow-by measurement establishes whether the problem is mechanical.
What to do about it
If cranking is slow, fix the electrical side first: battery, terminals, cables, starter. Replacing fuel components on a machine that cannot crank properly is wasted work.
If it cranks well and will not fire, bleed the fuel system properly and check for air ingress. If it then runs, the fault was air; find where it entered, because it will do it again.
If fuel arrives and there is no start, test the shutdown solenoid and the immobilizer before condemning the injection pump. Solenoid failure is common, inexpensive and frequently missed.
If fuel and electrical are both correct and compression is low, the engine needs mechanical work. Measure blow-by and compression to establish how much, and confirm cylinder kit requirements against the engine serial before ordering.
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Request a quoteFrequently asked
The engine cranks but will not start after I changed the fuel filter. What now?
Almost certainly air in the fuel system. Bleed it at the filter head and at the injection pump according to the procedure for that engine. If it will not hold prime, inspect the filter housing seal and the suction line — air is getting in, and no amount of bleeding will fix that.
Will not start when hot, but starts fine cold. Why?
A hot no-start is characteristic of injector or injection pump wear, where clearances open up at temperature and the system cannot build the required pressure. It is a specific pattern worth mentioning when you inquire, because it changes what we suspect.
How do I know if it is the starter or the battery?
Measure voltage at the battery while cranking, and at the starter terminal. A large difference between the two points to cables and connections. A battery that holds voltage at rest but collapses under cranking load has failed internally regardless of its resting reading.