Clogged fuel filter, closed shutoff valve, contaminated fuel, or failed fuel pump. The engine cranks but gets no fuel. Common after long storage periods when diesel degrades or after neglecting fuel filter changes.

What you'll see

The engine cranks at normal speed but won't start, or starts briefly then dies. Different from air-in-fuel because there's no fuel reaching the injectors at all. The exhaust is clean (no smoke) because there's no fuel to burn. After prolonged cranking, you might smell unburned diesel from incomplete combustion attempts. If the machine has been sitting for months, the fuel may have degraded -- old diesel turns dark, grows algae, and clogs filters.
Before you assume this is the problem

If the engine cranks slowly, check the battery first. If you can see fuel flowing when you open a line, the issue is more likely air-in-fuel or an injection problem, not starvation. See: Air in Fuel System, Weak or Dead Battery.

See all causes of engine won't start →

How to diagnose

  1. Check fuel level and shutoff valve

    Open the fuel cap and visually check. Don't trust the gauge. Also check for a fuel shutoff valve between the tank and the engine -- these are common on portable compressors and sometimes get accidentally closed during transport. Look for a lever or tap on the fuel line near the tank.
    Result: Fuel present, shutoff valve open.

  2. Inspect fuel quality

    Drain a small sample from the fuel filter bowl or water separator. Clean diesel is clear and straw-colored. If it's dark, cloudy, has particles, or smells sour, the fuel is contaminated. In cold weather, diesel can gel (wax crystals form) and won't flow through the filters. Diesel that has been sitting for 6+ months often grows microorganisms (diesel bug/algae) that clog filters.
    Result: Clear, clean fuel = fuel quality OK. Dark/cloudy/thick = contaminated fuel.

  3. Check fuel filters

    When were the fuel filters last changed? Portable compressors typically have a pre-filter/water separator and a main fuel filter. Both can clog. If the machine has been sitting with old fuel, the filters may be completely blocked. Try loosening the outlet of the fuel filter and cranking -- if no fuel comes through, the filter is blocked.
    Result: Fuel flows freely through filter = filter OK. No flow = blocked filter.

  4. Check fuel shut-off solenoid

    Diesel engines have a fuel shut-off solenoid that must be energized to allow fuel flow. You should hear it click when you turn the key to the 'on' position. If it doesn't click, check for power to the solenoid -- it's powered through the safety relay circuit. A tripped safety device will de-energize this solenoid, preventing fuel flow and thus preventing starting.
    Result: Audible click when key turns on = solenoid OK. No click = check power supply and safety circuit.

How to fix it

  1. Replace fuel filters

    Replace both fuel filters. Pre-fill the new filters with clean diesel before installing -- this reduces air in the system and gets you started faster. After installing new filters, bleed the fuel system using the hand primer pump.

  2. Drain and replace contaminated fuel

    If the fuel is contaminated, drain the entire tank and fill with fresh, clean diesel. Also drain the water separator. In severe cases (algae growth), the fuel tank itself needs cleaning. Add a fuel biocide to prevent future contamination if the machine sits for long periods.

  3. Fix the fuel shutoff solenoid circuit

    If the solenoid isn't clicking, check the safety relay circuit. All safety switches (engine oil pressure, engine temperature, compressor temperature, emergency stop) are in series. If any one is open or has a loose wire, the safety relay drops out, which de-energizes the fuel solenoid. Check each safety switch and its wiring. See the engine shutdown troubleshooting section for the full safety circuit diagnosis.

Common mistakes

The biggest mistake is running portable diesel compressors until the tank runs dry. When you run out of fuel, air enters the entire fuel system including the high-pressure side, which is much harder to bleed than the low-pressure side. Always refuel before the tank is empty. Also: don't forget to check the fuel return lines back to the tank -- if a return line is blocked or kinked, fuel pressure builds up and the injection system malfunctions.

Parts & tools

Fuel filters (both pre-filter and main). Clean diesel fuel. Funnel and container for draining. Open-end wrenches for fuel connections. Fuel biocide additive for long-term storage.

Review safety precautions before starting →

Safety

Don't crank for more than 15-20 seconds at a time. Wait 30 seconds between attempts to let the starter motor cool. Excessive cranking will burn out the starter.

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