L5P Injector Problems - Here's How Duramax Can Let You Down

Do you own a Chevrolet Silverado HD or GMC Sierra HD with the 6.6-liter L5P V-8 Duramax Turbo Diesel Engine? Do you suspect one or more L5P injector problems? If you have noticed excessive smoke, power loss, or rough idling, chances are your Duramax diesel engine has faulty injectors.

Injection problems highlights

• Level of importance:High
• Can you drive?Usually, yes
• DIY inspection:Possible but complicated
• DIY repairs:Mostly,impossible
• Price of repair:$350 - $850
• Commonreasons:Clogging, age, electrical problems
• How to fix:Verify electrical connectors, clean the injectors, swap them to see if the codes change

How Do Fuel Injectors Work In Diesel Engines?

Fuel injectors are tiny engine parts that send fuel directly into the intake manifolds via spray. In a diesel engine, this process takes place in front of the intake valve.

Diesel fuel injection systems are pretty different than gasoline. In a gasoline engine, there's a port engine or carburetor used to inject fuel before the intake stroke, that is, outside the cylinder, where the gas mates with air before entering the cylinder. In a diesel motor, fuel injection takes place directly in the cylinder.

Diesel injectors are very complex. Diesel engine cylinders produce intense heat and pressure. For effective fuel combustion, the injectors have to withstand those conditions and, at the same time, distribute the diesel fuel in a fine mist. And for complete combustion, there has to be an even distribution of the mist throughout the cylinder.

L5P Injectors

The 6.6-liter L5P V8 Duramax is part of the GM-manufactured series of turbo diesel engines. The series has seen tremendous improvements since it was first launched in 2001. The L5P has eight injectors.  

General Motors produced the L5P Duramax between 2017 and 2021 to replace the Duramax LML. The LML uses piezoelectric injectors, replaced by solenoid-style injectors in the L5P unit. Although Piezo injectors are generally quieter and higher-quality than Solenoid, General Motors used advanced technology to improve injectors. As a result, the L5P injectors perform better than the Piezo injectors in the LML.

The L5P Solenoid-style injectors are highly advanced. Thanks to the G4S third generation units from Denso, the L5P injectors flow approximately 20 percent more diesel than the LML injectors. The Denso injectors have seven mini-sac nozzles used as fuel atomization aids and help minimize emissions.

Each injector in the L5P carries out a maximum of seven injection events in every combustion cycle. As a result, there are several pilot events to help quiet the engine and one or more post events to enhance emission control.

How Do I Know If I Have L5P Injector Problems?

Are you having trouble with your Chevrolet or GMC Duramax fuel injectors? It could be time to replace these important components of your L5P V8 Duramax turbo diesel engine. But how can you tell it's time for a replacement?

Whether you are a seasoned or beginner heavy-duty truck driver with one of these HD GM trucks - the Sierra or Silverado - you already know that your fuel injectors must work correctly for optimal engine performance. And although the LB7 built between 2001 and 2004 is known to be the most notorious Duramax with faulty injectors, all engines develop bad injectors at some point. And that includes the L5P injectors.

However, many drivers ask themselves; what causes my L5P Duramax injectors to go bad? Read on for signs of faulty L5P injectors, causes, and how you can get yourself out when you realize you have bad injectors.

Symptoms of L5P Injector Problems

If you suspect your L5P Duramax has bad injectors, check out for the following symptoms.

• Excessive Smoke

If your HD Duramax truck blows too much smoke, it shows faulty fuel injectors. On many occasions, if your tailpipe pushes out excess smoke, especially at idle when the engine has reached operating temperature, you have a worn-out injector.

If the excessive smoke is white, too much diesel fuel is injected into the chamber, or there is not enough heat to burn the fuel. Unburned fuel exits the system through the exhaust tail pipe. It'll have a rich scent of raw diesel. White smoke can also be caused by insufficient compression or coolant in the combustion chamber.

Excessive black smoke is a sign of worn-out or leaking injectors. This means too much fuel goes into the combustion chamber, and there's insufficient air supply. Excessive black smoke can also happen due to air intake system restrictions.

You could also experience excessive blue smoke, but injector problems don't cause this. Blue smoke is caused by engine oil burning in the combustion chamber with fuel. Worn pistons and low compression are the main culprits.

• Power Loss

There are several ways a bad injector will mess up your engine performance. One is when the injector o rings have gone bad and have leaked enough to cause a problem with the fuel-air ratio. If you have a faulty o ring, your HD truck will experience a hard start, misfire, or power loss. Bad o rings will also cause poor acceleration and excessive fuel consumption. If the problem is too severe, you experience engine stalling.

Another way faulty injectors can cause power loss is when they cannot supply enough fuel to the combustion chamber. Injectors provide fuel to the chambers by spraying at high pressure. GM engineers ensured the advanced Denso injectors in the L5P were perfect for supplying enough fuel for optimal performance. A slight miscalculation can mess up the system and result in several problems, one of which is engine power loss. One of the primary reasons a fuel injector fails to spray sufficient fuel is carbon buildup - this happens when you feed your L5P Duramax engine the wrong or low-quality fuel.

• Rough Idle

There are several reasons your L5P Duramax vibrates excessively at idle - improper engine mount, exhaust system components contacting the vehicle frame, weak cylinder compression, and a faulty fuel injector.

If the fuel injectors on your truck are dirty or clogged, your vehicle will vibrate, shake or shutter while idling. The reason is that the clogged injectors interrupt fuel from constantly flowing into the combustion chamber. You can have the injectors cleaned, and if the problem is severe, replace them.

Other symptoms

• Hard or no start
• Fuel in oil
• High return fuel

If your Duramax diesel truck is experiencing one or some of these signs, it is time to check your fuel injectors. Bad injectors could allow engine coolant or fuel to mix with oil. These are not lubricants, and making their way into your oil supply could result in more severe problems down the line. Contaminated oil is bad for the turbocharger in your L5P Duramax diesel engine.

What Causes L5P Injector Problems?

Nobody wants to go through the same problem twice. In the same way, if you have replaced the fuel injectors in your Duramax L5P engine, you want to avoid a repeat in the future. As such, you want to know why they failed so you can avoid it. Although injectors are components that will eventually wear out, proper maintenance can lengthen their lifespan.

Here are a few causes of fuel injector failure.

• Poor Quality Fuel

The quality of the fuel you feed your truck can affect the performance of the engine fuel injectors. Avoid fueling at slow-moving fuel stations. If diesel sits for a long time, it is prone to contamination and dangerous to your diesel injectors. Avoid cheap fuel. They say cheap is expensive in the long run.

• High Temperatures

High pressure and temperatures are two dangerous elements to your fuel quality. This is not about the fuel you feed your truck. You can use the proper fuel quality, but the fuel gets contaminated in your tank due to high temperatures and pressure. Degraded fuel leaves deposits in the fuel pump and injectors. As a result, these deposits will lower the lubricating ability of the diesel.

• Operating In Bad Conditions

Your L5P Duramax is a mechanical machine. It requires the right conditions to function correctly. There are several conditions that can temper your fuel injectors. These include short drives, excessive idling, driving in cold areas, and light engine loadings. Bad conditions can lead to deposit problems in the fuel injectors and combustion chamber, exhaust spaces, and the turbocharger.

What Next

If your fuel injectors are faulty, one of the best and long-lasting solutions is to replace them. You can also have them cleaned. Visit a Chevrolet or GMC service center close to you, and have a professional mechanic diagnose your L5P Duramax for injector problems.