Lack of diesel fuel, Blocked fuel filter and Fuel pump failure are the most obvious cause of diesel generator cranks but won't start. If all the above have been checked out, and operational, then the last resort will be a faulty fuel stop solenoid.

Diesel generator cranks but won’t start. Try again and diesel generator still cranks strongly but won’t start.
Check the following:

1, Do you have enough diesel fuel in the fuel tank?

If YES, and the Diesel Generator cranks but won’t start? The most likely issue is the lack of fuel supply in the diesel engine.

2, Is the fuel supply line and joint cracked, constrained, bent, or ruptured?

If good, then this is fine; if NOT, fasten the joint and replace it with a new fuel supply line if necessary

3, Check if there is diesel fuel leakage in fuel injectors

Loosen the fuel supply line to a cylinder, Check if there is diesel fuel leakage through the joint when starting the diesel generator. If there is diesel fuel leakage, and the Diesel Generator cranks but won’t start? then it's NOT the fuel supply line.

4, Check the fuel stop solenoid valve.

If Good, then this is fine; If NOT, and the Diesel Generator cranks but won’t start? replace it with a new stop solenoid valve

5, Is the diesel engine warm to the touch?

If the answer is YES, then the block heater is working.

6, Is the Air Inlet and exhaust not blocked?

If NO blockage, then this is fine

7, Are Fuel filters or Pre-filters not blocked with dirt or debris?

If the fuel filters are good, then it’s NOT the fuel filters, If NOT, replace them with new fuel filters and Pre-filters

8, Are Air filters not blocked with dirt or debris?

If the air filters are good then it’s NOT the air filters. If NOT, replace them with new fuel filters and Pre-filters

9, Check the Start batteries' Voltage and Connections

Just like your car, Diesel Generator cranks but won’t start? it could be due to a dead battery or faulty connections. Check the start batteries' Voltage and connection, If the batteries' voltage and connections are good,  then the battery is not likely the problem.

10, Low Lube Oil Level in the Engine

Lube Oil is vital to your diesel generator’s engines. While most diesel generators have a sensor to let you know when oil levels run low, it is still essential to check the oil levels with a dipstick. If you have low oil, refill with the right type of oil as directed by the manufacturer. This could be an excellent time to replace the oil filter to keep your diesel generator in good condition and avoid costly breakdowns and emergency repairs.

The most obvious easy fix- diesel generator cranks but won't start

• Lack of diesel fuel supply is the most likely reason

There may exist some air in the fuel supply line mostly happening at the first generator starting or long-time no running. This causes the diesel fuel to drop back and not enter the diesel engine body. bleeding the diesel fuel to the diesel engine by manually pumping fuel or turning the primary bleed screw. Check your generator manual for its location. Then gently turn the screw to allow the air to escape and then re-tighten once fuel begins to appear at the screw.

• Blocked fuel filters

Lack of servicing and not renewing the fuel filters over time will cause them to become inefficient and finally block with dirt. Replace the fuel filters.

• Fuel pump failure

It can happen but it’s rare.

• If all the above have been checked out, and operational, then the last resort will be a faulty fuel stop solenoid. A faulty solenoid, won’t allow the injection pump to push fuel through the lines to the injectors. Replace the solenoid.