Why You Experiences 5.9 Cummins Problems – Five Issues and Solutions

Dodge Cummins values longevity and simplicity when making its engines. One of the longest-serving engines is the 5.9-liter engine that emerged in 1989 and ended in 2007.

Even if most people know about the Dodge 5.9 Cummins problems, they still choose this engine. As one of the most popular diesel engines, 5.9L is a reliable option if you disregard its fuel system failures.

“Fuel system failure is the most widespread problem with the 5.9-liter engine. Others include engine block cracks, Fuel Control Actuator failure, leaky exhaust manifold, etc.”

We will expound on these problems shortly. 

Overview of the 5.9 Cummins

Found in Dodge RAM trucks, the 5.9L inline six-cylinder engine has existed for decades. Check how the first engine evolved over the years next.

5.9 12V, 6-cylinder engine: 1989 to 1998

In 1989, Cummins made its first 5.9L 12V diesel engine. Then, it continued releasing the same engine, but with advanced features, until 1998.

Originally, the 5.9L engine offered only 160 horsepower at 2,500RPM. By 1998, the 5.9liter 12V 6-cylinder engine offered up to 215hp at 2,500RPM.

Regarding the torque, the 5.9L initially offered 400 lb-ft at 1,600RPM. By 1998, the engine had 440lb-ft at 1,600RPM.

Made from cast iron, the 5.9 engine block had 6 inline cylinders, cast iron cylinder heads, and a displacement of 5.9l (359cubic inches).

As for the fuel system, it first donned the direct injection Bosch VE44. By 1998, the engine’s fuel system was direct injection Bosch P7100.

Back then, the Valvetrain was OHV; it had two valves in each cylinder. By mid-1991, Cummins had introduced the turbocharged aspiration.

5.9L 24V/ISB: 1998 – 2007

By the year 1998, the 5.9 Cummins engine was advanced. While the first 1989 engine offered only 160hp at 2,500RPM, the initial one of 1998 provided 215hp at 2,700RPM.

By 2007, the 5.9L 24V could provide up to 325hp at 2,900RPM. Torque for the first engine was 420lb-ft at 1,400RPM and then 610lb-ft at 1,600RPM in 2007.

Still, the engine configuration was an inline six-cylinder with the same displacement of 5.9 liters (359cubic inches).

Cummins used cast iron to construct the engine block and cylinder head and retained the turbocharged aspiration.

Vehicles produced between 1998 and 2002 had the same direct injection fuel system.

In 2003, Cummins introduced the direct injection-common rail fuel system. Lastly, the valvetrain was still OHV but with four valves per cylinder.

6.7L ISBE engine – 2007 to now

After 2007, the production of the 5.9liter 12V and 24V engines stopped. Cummins introduced a new engine with a displacement of 6.7L (408 cubic inches).

Between 2007 and 2022, the horsepower changed from 350 to 385 in the 2,800RPM to 3,013RPM range.

Torque for 2007 models was 610lb-ft at 1,500RPM and has increased to 900lb-ft at 1,700RPM in 2022.

Aspiration is still turbocharged, and the construction material for the cylinder head and the engine block is cast iron.

Cummin’s 6.7liter engine is an inline 6-cylinder engine with an OHV valvetrain and four valves per cylinder. Again, 2007 to current models use the direct injection-common rail fuel system.

Dodge Ram 5.9 Cummins Common Problems and Solutions

Cummins 5.9L V12 and V24 inline 6-cylinder engines are a darling to most people. Even if several users find the 5.9L Cummins reliable, it does not mean that it has no issues.

Cummins 5.9L has a few problems that are not very strange. We will discuss these problems below and provide viable solutions. Can we start?

Problem 1: Fuel Injector Failure

As noted above, some Cummins 5.9L engines use the direct injection-common rail fuel injection system.

Although the system can deliver fuel into the engine at a massive pressure of 27,000psi, it is too sensitive to diesel.

Diesel usually contains some degree of water and dust particles.

If you do not change your fuel filters often, this dirty diesel can end up clogging the micro parts of the direct injection-common rail system.

After that, insufficient fuel will reach the pistons, and some of it could leak into the engine.

According to most users, this problem can begin from around 150,000miles.

Symptoms that can show when fuel injectors are clogged up include having fuel in your engine oil. You can also notice that your vehicle has more smoke and some knocking sounds.


There is nothing you can do with faulty fuel injectors except replace them. Spare parts that can offer better performance than your factory injector is available online.

Some have the same size as the factory ones and can match their performance. Note that the 5.9 fuel injector will fit in any head, and it is the right choice.

If you install an older fuel injector into a newer engine, that could change the spray angle negatively.

Instead of solving the fuel injector problem, you could begin a sequence of other issues, including high EGT, rough idling, less engine power, and damage to the engine.

Call a professional if you are unsure of the parts to select to avoid facing the mismatch consequences.

If you need to change the complete set of fuel injectors, the cost is two thousand dollars or more. Once you install new injectors, make sure you change your fuel filters often.

Problem 2: Fuel Control Actuator Failure

Vehicles using the Bosch CP3 injection pump have a Fuel Control Actuator. While the PC3 injector is remarkably reliable, the Fuel Control Actuator is at risk of failure.

FCA regulates the quantity of fuel pressure that the CP3 pump can offer.

During idle, the FCA restricts fuel flow and keeps the fuel pressure level down. When more fuel is necessary, the FCA allows more of it to get into the CP3 injector, raising the pressure.

Proper operation of the Fuel Control Actuator depends on the signals emerging from the ECM to the CP3.

As the FCA has mechanical and electronic moving parts, some of these can clog up or get stuck. After that, you might notice several engine issues, including rough idle, low engine power, lower rail pressure, etc.


If your Fuel Control Actuator fails, you have no choice but to get a new one.

Meeting installation costs is unnecessary because you can follow easy instructions and replace the FCA at home. Also, the item costs less than $200 online.

Problem 3: Damaged Fuel Pressure Relief Valve 

Another component of the 5.9liter engine prone to failure is the Fuel Pressure Relief valve. Once it fails, the open valve will have no rail pressure as the fuel flows back to the tank.

Usually, the leading causes of this problem are blockage in the valve seat due to dirt or damaged internal springs.

One way to know that you have a faulty Fuel Pressure Relief valve is to check if you have similar symptoms as those of a faulty FCA.


Purchase a new Fuel Pressure Relief valve online. Bosch FPR valves do not cost much if you have a hundred and thirty dollars you can get one. 

Problem 4: Stock Lift Pump Failure

Dodge trucks use a lift fuel pump that extracts fuel from the tank and delivers it to the injection pump. Although it works well first, it is prone to failure soon after.

Earlier 5.9L models had a lift pump fitted to the side of the engine block. They did not perform well, so the manufacturer introduced the in-tank fuel pump.

According to users, the in-tank fuel pump is better than the initial style but has its share of problems.


If your fuel pump fails, replace it with a new one. However, we advise against buying another stock fuel pump if you want to make your engine more powerful.

Instead, choose an aftermarket fuel pump with a higher capacity and lower risk of failure because of an advanced inbuilt filtration system.

As the aftermarket lift pump would deliver cleaner diesel to the CP3, the injectors can last longer. Ensure that you select the correct product based on the type of stock lift pump you currently have.

Problem 5: A Leaky Exhaust Manifold

Cummins models using the 5.9L V12 or V24 engine have an exhaust manifold that is ever in danger of failure.

A typical exhaust manifold features cast iron as the construction material, which is prone to cracks due to rapid expansion and contraction.

If your manifold develops cracks, there will no longer be adequate pressure to raise engine power.


If your manifold has leaks, you should buy a new one. Like other parts above, replacing an old exhaust manifold is a manageable task if you love repairing cars.

Note: Engine block cracking is a rare problem affecting only the Brazilian engines made from 1998 to 2004. Probable causes of this cracking could be rust, coolant pressure, or excessive towing.

 Is the 5.9 Cummins a Good Engine?


Yes, the 5.9liter, 12-valve, inline 6-cylinder engine is good. As it can provide 29mpg on the highway and 24 mpg in the city, the 5.9l Cummins diesel engine is simple and durable.

People love this engine because finding aftermarket spare parts is easy and quick.

Besides being easy to maintain, the original 5.9liter engine offers better fuel economy than the latter 6.7L engine.

Cast iron material assures longevity to all those who own or plan to purchase the 5.9L engine. Furthermore, the cast-iron block consists of a super durable steel crankshaft and connecting rods.

Even if you get a high-mileage second-hand truck, the 5.9L 12V engine will still perform well. Bosch high-pressure common-rail direct fuel injectors are prone to failure but are also easy to change.

How Many Miles Will a 5.9 Cummins Last?

According to the manufacturer, the 5.9L Cummins engine can last 350,000miles without failure. As earlier hinted, the 5.9L engine has a frail fuel system.

Most of its components are likely to fail before covering 350,000 miles.

But we like the Bosch P7100 fuel pump as it can last between 500,000 and 700,000 miles.

Pistons, crankshaft, connecting rods, and other internal parts are durable at 500,000miles.

If you want your engine to cover several miles before the damage, take diligent care of it. Check the water pump and the oil level often.

Replace the fuel filter regularly to prevent dirt from clogging up the injectors. Moreover, change the coolant and transmission fluid often to extend the mileage of your 5.9L engine.

If you use your truck for regular towing and less often drive it on tarmac roads, maintain it more often than necessary.

What are the Dodge 5.9 Cummins Diesel MPG

Any 4WD truck running on the 5.9L Cummins engine is a no-regret choice. In most cases, it will provide 29mpg on the highway and 24mpg in the city.

A 5.9liter has better fuel economy, longevity, speed, and pulling power. If you maintain fluid levels where they need to be, you might slightly increase MPG.

Are 5.9 Cummins Reliable?

Countless people seek the 5.9L Cummins engine because it is reliable. If we ignore its problematic fuel injection system, the 5.9L engine is a good deal. Even if it has fuel system issues, these are easy to solve.

Unless you need to change a complete set of fuel injectors, you will incur a small cost. As a 5.9liter engine block features cast iron and steel internal parts, it assures longevity to those who love it.

Lastly, if you maintain your truck before schedule, you will catch various 5.9 Cummins problems early and solve them.

How affordable are 5.9L spare parts?

First-generation 5.9 Cummins vehicles have several spare parts. You do not even have to install stock spares as there are equally good-performing aftermarket options you can buy online.

With less than a hundred and fifty dollars you can solve some of the problems we discussed earlier.

Which Cummins model should I buy?

We discussed the 5.9L V12 and V24 engines and the newest 6.7L ISBE version. Regarding the best engine to choose between these, it depends on your tastes and preferences.

If you like a truck with advanced engines and features, then choose a model made from 2007 to 2022. If you do not mind an older model, get a 5.9L V12 truck.

Which model year trucks experience lift pump failures more often? 

Avoid the 1998 to 2004 model year vehicles using the 5.9l 24-valve inline 6-cylinder engine because of frequent lift pump failures.

Cummin’s first models had an engine-block lift fuel pump that triggered excess heat buildups, leading to engine misfires, rough idling, and stalling.

Final Words

We have been evaluating various cummins 5.9 problems. As you may have noted, this engine’s core problem is its fuel system.

No wonder most of its failures relate to fuel delivery and injection. Assuming this problem was absent, the 5.9L engine would be excellent.

Most people consider it a good engine and continue to use it. Now it is upon you to decide if you want to buy a truck using the 5.9liter inline 6-cylinder engine.