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5.9 Cummins Injection Pump

5.9 Cummins Injection Pump Problems

More often than not, it’s challenging for vehicle owners to even notice the most common 5.9 Cummins injection fuel pump issues such as hard starting, lack of power, or not starting at all. A bad injector pump can cause more serious issues in the fuel system, particularly in the injector control circuit, or worse, kill the Cummins diesel engine.

With Titan Diesel, we will help you determine these common problems and share the most effective tips on how to repair Cummins lift pumps as well as how to check fuel injectors and their valve cover gasket on 5.9 Cummins. Keep reading and learn more about the glaring signs of a broken lift pump.


Signs of a Broken Lift Pump


​Signs of a Broken Lift Pump

With 5.9 Cummins engines, there are two fuel pumps to keep in mind. The first is the lift pump which basically lifts the diesel fuel to the injector pump from the fuel tank. Then, the fuel is sprayed into the engine. You need to use a scanner to check the fuel system components including the fuel filter and assess poor engine performance.

You probably haven’t realized that your new lift pump is broken until the vehicle malfunctions and stops working after slow deceleration. In fact, the injection pump continues to pull fuel from the lift pump despite having some issues like blue-white smoke.

The problem is that the lift pump doesn’t have enough force and contribution rates to perform properly. Therefore, the lift pump will affect the performance of the Cummins 5.9l injection pump including the engine, tank, and cylinder.

Now, the lift pump will become problematic due to lack of pressure and eventually experience loss of power. The engine will suffer and become hard to start or won’t start at all until it is replaced. Lift pumps are an unsung hero for all types of vehicles including SUVs, trucks, and sedans.

If you notice the following symptoms, contact Titan and we will help you repair these problems with your lift pumps and maintain quantity balance:

  • The engine overheats easily. An overheating Cummins engine is one of the common symptoms of a broken lift pump as it wears out over time. The heat and smoke coming from the dying injector pump cause the car engine to overheat and crank until you experience engine stalling.
  • Sudden loss of power. If the lift pump goes out, the Cummins diesel engine will experience power loss even if it doesn’t sputter. The lift pump is not lifting enough fuel, hence the power engine can’t perform well enough, especially for trucks going uphill.
  • Sputtering engine. If the Cummins engine sputters when you drive faster, it indicates that the engine is not getting enough diesel fuel to continue running. It could be due to a bad lift pump, clogged fuel injectors, or a spark plug that needs replacing.
  • Low fuel pressure. To find out why your lift pump is cold and dying, you need a fuel pressure gauge to test the pressure point. Get a friend to rev the engine while you read the gauge. Check your manual to see the advisable fuel pressure for your Cummins 5.9l vehicle.
  • Reduced fuel mileage. If the calculated fuel flow exceeds the amount the trucks’ engines should receive from the lift pump injectors, the trucks will not get the average gas mileage they should. To maintain fuel efficiency and avoid an engine block or injector misfire, tracking your fuel mileage performance is important.
  • The engine is experiencing surges. When the Cummins lift pump is transferring too many fuel lines to the Cummins 5.9l diesel engines, it may lead to surges and serious engine damage. This is dangerous because the car will pick up speed and then drop quickly.


Checking Injector Pump on 5.9 Cummins


​How to Check Injector Pump on 5.9 Cummins

Checking the fuel injectors on Cummins 5.9l engines requires a scan tool to diagnose symptoms and find the leak in the cylinders. It’s not advisable to manually detect any leak because the fuel system has 25,000 PSI of pressurized fuel. This means it can cut your skin and the fuel may get into your bloodstream which is fatal.

The first step is to record and replace active DTCs using the scan tool since they can show the cause of the same issue. Make sure you have enough fuel pressure supply and clean fuel. If the Cummins 5.9l diesel engine is hard to start or doesn’t even start at all, the problem could be the Cummins diesel fuel supply and pressure are not enough to reach the fuel injector pump.

The rail pressure should have 4,000 PSI or higher when cranking, anything lower than that point can be caused by a bad fuel pump and cylinder. Usually, starting and cranking symptoms are due to low rail pressure and performance, so make sure to check on the injectors. We can help you use diagnostic trouble codes and other codes related to repairing or replacing your Cummins 5.9l injector wear.