What Happens When Cam Phaser Goes Bad?

When a cam phaser goes bad, it can damage your engine’s VCT solenoid which is controlling the engine valve’s timing by allowing the oil to flow under a certain pressure through the cam phaser. The ECU unit will also turn on the check engine light. The engine can suffer from a lot of different problems, such as knocking and rough idling. Cam phaser issues in vehicles can also lead to engine damage, such as bent or cracked camshafts, cracked heads, damaged valve lifters, damaged rocker arms, etc. Resultantly, your engine will not rev up to its full capacity. You will notice that your engine sounds like it is not revving up. The engine will also feel sluggish and it will not accelerate well.

The cam phaser is a mechanical component that allows the camshaft to adjust the timing of the valves with the changing RPM of the car to increase the efficiency of an engine. So, what happens when cam phaser goes bad?

What are the causes and symptoms of a bad cam phaser? Read this guide till the end to know everything about the cam phasers.

Some Key Insights for You
  • Cam phaser is responsible for engine efficiency, emissions, and optimum horsepower. It adjusts valve timing using oil pressure.
  • Wear inside cam phaser, low oil pressure, and debris in oil can cause cam phaser failure.
  • Symptoms of bad cam phaser include engine knocking, poor fuel economy, loss of power, check engine light.
  • Replacing a broken cam phaser costs $2,000 to $5,000. Involves timing belt, phasers, tensioners replacement.

What Are Cam Phasers?

A cam phaser is a hydraulically driven component that adjusts the engine’s valve timing so that the engine is running at the right speed, and with higher fuel efficiency.

Cam phaser adjusts the camshaft, which controls the opening and closing of the intake and exhaust valves in the cylinder.

Cam phaser is connected to the camshaft. The cam phaser uses oil to change the valve timing of the engine. In this way, a cam phaser is responsible for engine efficiency, emissions, and optimum horsepower.

Read this guide till the end as I will share the proper working of cam phasers with illustrations.

Cam phaser works with the camshaft to control the timing of the inlet and exhaust valve of an engine. On the camshaft, cams create an eccentric path when they rotate.  

The cam path is designed for opening and closing the inlet and exhaust valves of an engine. Cam phaser plays a vital role in the variable valve timing mechanism of the engine.

Variable valve timing systems in the engine were introduced to control the opening and closing of engine cylinder valves at higher speeds so that the vehicle’s quality can be enhanced in terms of fuel economy, performance and emissions.

A cam phaser operates with the following components:

  • Timing belt (also called sprocket chain)
  • Timing gear (also called cam sprocket)
  • Camshaft
  • Solenoid Valve
components with which cam phaser operates

Cam phasers have small chambers that contain oil under pressure. That oil pressure is responsible for shifting the angle of cams on a camshaft so that its timing can be advanced or delayed in response to the control signals sent to the solenoid valve by the electric control unit (ECU) of the engine.

cam phaser schematic

As you can see in the picture above, there are three main parts of a cam phaser

  • Stator (Outer part): Connects with the timing gear
  • Rotor (inner part): That is responsible for rotating the camshaft
  • Oil chambers: That receive the oil under pressure

So, basically, the timing gear is connected to the crankshaft of the engine through the timing belt. The gear is connected to the outer part of the cam phaser through the locking piston.

So, the motion of a timing gear is transferred to the cam phaser through the locking piston. Through cam phaser, the camshaft starts rotating as it is passed through the inner part of the cam phaser. I have shown the locking piston of cam phaser in the figure below:

locking piston in a cam phaser

When the oil flows through the chamber of the outer part of a cam phaser, the piston (locking pin) is pressed and the cam phaser is disengaged from the timing gear.

During this cycle, the oil pressure turns the inner part of a cam phaser through a certain angle, which is responsible for the variable valve timing of an engine.

I found this video on Youtube highly helpful to understand the concept of a phase shift in the cam phaser. You can start watching it at 4:20 time. The video is shown below:

Here is another video animation to understand the working of the Variable Valve Timing System.

Why does a Cam Phaser Goes Bad?

There are following three main reasons for the failure of a cam phaser:

  • Wear inside the cam phaser
  • Wear in the engine and low oil pressure
  • Debris in the oil

1. Wear Inside the Cam Phaser

There are two main components subject to wear inside the cam phaser – the rotor vanes and stator bore. Here’s a closer look at how wear occurs in each place:

Rotor Vanes:

  • The rotor vanes of the cam phaser slide in and out of the stator bores as timing is adjusted. This causes wear over time.
  • Vane tip wear results from constant contact with stator surfaces.
  • Small pieces of metal can break off and score rotor and stator surfaces.
  • Excess vane tip clearance from wear allows too much oil to bypass vanes. This reduces phasing control.

Stator Bore

  • The rotor vanes ride against the stator bore surfaces. Friction from contact gradually wears down surfaces.
  • Wear increases clearances between stator bores and rotor vanes. This reduces phasing accuracy.
  • Severe bore wear allows the rotor to wobble excessively, damaging internals.

What’s the result of this wear?

Enlarged clearances from wear reduce phasing responsiveness and accuracy. This causes valve timing to be erratic.

Moreover, the worn surfaces of the cam phaser and the wobbling of its parts allow oil to escape from the phaser. This causes low oil pressure faults.

2. Wear in the Engine and Low Oil Pressure

Eventually the amount of wear inside the cam phaser reaches a point where normal phasing function is no longer possible.

This results in complete cam phaser failure. At this point, the check engine light is on, the engine runs very poorly or not at all, resulting in excessive engine wear.

As the engine wears, more oil is lost through the crank, engine rod, and cam bearings. Since the cam phasers are the last component to receive oil, not enough volume of oil is delivered to control the cam phaser. So, the cam phaser rattles back and forth.

Due to low oil pressure, the 5.4L V8 engine has the most issues with the cam phaser. The issues in the 5.4L engine of Ford used to arise because variable cam timing phasers could no longer be controlled by the ECU due to wear in the phaser or lack of oil pressure delivered to them. Due to this reason, Ford replaced the 5.4 V-8 in 2010 with the 411-horsepower 6.2-liter V-8.

3. Debris And Sludge In Oil Due to Infrequent Oil Changed

Inside a running engine, metal parts are constantly moving and generating friction. This inevitably produces tiny microscopic bits of metal that then circulate in the oil.

The oil also picks up combustion byproducts, environmental contaminants, and even traces of fuel that seep past piston rings. Over time, all these substances accumulate to form sludge and deposits referred to collectively as “dirt and debris.”

Particles in dirty oil can clog small passages in the cam phaser solenoid that regulates oil flow and pressure. This affects the phaser’s ability to change cam timing.

Moreover, contaminant deposits can cause cam phaser components to stick and stop moving properly. This prevents cam timing from advancing or retarding as needed.

So, you should follow the vehicle manufacturer’s oil change interval recommendations! For most modern engines, this is around 5,000-10,000 miles or 6-12 months under normal driving conditions. You can check my guide on why is it bad to change oil after 2 years.

I also recommend you always go for quality OEM oil filters. They are expensive but work effectively, and can prevent costly engine repairs in the longer run.

How Do I Know If My Cam Phaser Is Bad?

Here are the signs that will show that your cam phaser is bad:

1. Engine Clicking Sound and Misfire

If your engine knocks too much, it is an indication that your cam phaser is bad.  The clicking sound in the engine is produced due to the poor oil pressure condition when the cam sprocket wears off. As a result, you will hear the rattling noise from the front of the engine.

A bad cam phaser also shows the signs of a misfire. A bad cam phaser causes the engine valve timing to go out, due to which incomplete fuel combustion takes place, causing the engine to misfire.

You can hear the cam phaser rattle sound in this video:

2. Poor Fuel Economy and Reduced Engine Performance

A cam phaser adjusts the timing of the engine valves in order to improve fuel economy and reduce emissions. When a cam phaser goes bad, it can cause poor fuel economy and increased gas emissions due to inefficient combustion.

When engine valves will not be lifted or closed at the right time, the required amount of fuel and air could not be entered into the engine cylinder, due to which inefficient combustion will take place. Resultantly, your vehicle’s performance will be affected.

3. Loss of Engine Power

When the camshaft phaser is faulty, the car will not accelerate smoothly. If you notice that the engine starts hesitantly, the engine could be losing fuel.

This could be caused by a faulty camshaft phaser. If your car speed doesn’t go above a certain rpm due to reduced engine power, it also indicates that the cam phaser of your engine is bad.

4. Check Engine Light Illuminated

When the cam phaser is faulty, the engine light will be illuminated. CEL does not illuminate in all cases when the cam phaser goes bad.

According to some people, they have only faced a rattle on cold starts, or their engine has lost power. So, apart from CEL, loss of engine power and knocking sound are the strong symptoms that show that your cam phaser has issues. 

However, if your engine runs rough after warming up, chances are that the check engine light will be illuminated. The ECU unit of an engine throws an error code, due to which CEL starts glowing.

ECU unit of a vehicle tries to protect your engine from the effect of bad cam phasers. ECU tries to keep your engine in limp mode and prevent the engine from exceeding a certain rpm. When the check engine light turns on, the engine won’t be able to go above a certain rpm i.e. 30 to 40 mph.

What Is Cam Phaser Rattle?

The most common cause of cam phaser rattle is a worn-out locking pin. The locking pin is the small metal piece that keeps the cam phasers locked into the timing gear. If the locking pin is broken, the cam phaser will not lock into place, and it will cause a cam phaser rattle on engine startup.

As a result of this, your car may also rattle at idle.

Is It Worth Replacing Cam Phasers?

Yes, if they are faulty or damaged. If you do not replace damaged cam phasers, they can destroy a VCT (Valve control timing) system which will result in engine exhaust valve timing problems.

The problem with the cam phaser is that it has a small mechanism that can get stuck. When a cam phaser is stuck, it can cause damage to the intake and exhaust valves of an engine. Resultantly, both valve timing problems would cause a loss of power. In my experience, when your cam phaser is illuminating the check engine light, it is time to replace it.

Cam Phaser Replacement Guide

Cam phaser replacement is a quite tricky process. I would highly recommend you to take your vehicle to the respective dealership to replace the cam phaser. They have vehicle service manuals and the required equipment to get it done. So, instead of replacing the cam phaser on your own, you should take it to the dealership.

As a piece of general information, here are the basic steps we need to follow to replace a cam phaser:

  • Disconnect car battery
  • Remove the valve covers and crank pulley
  • Remove all items on the front cover i.e. belt, power steering, fan
  • Remove all bolts of a chain cover
  • After that, following your vehicle’s manual, remove the parts in order of their number
  • Now inspect a damaged cam phaser. It could have issues like broken locking pin, deformed spring, etc.

For more details, I found this forum thread on the cam phaser replacement guide helpful.

What Is The Cost of Replacement of Cam Phaser?

Replacing a broken cam phaser is a costly procedure. It can cost anywhere between $2,000 to $5,000. This cost is a sum of labor cost and the cost of OEM parts. It is a complete repair kit that includes a timing belt, cam phaser, tensioner, and sprockets. These kits usually do not contain VCT solenoids.

Your mechanic will decide after inspection whether it needs a new VCT solenoid or not. You can find the price of a cam phaser by visiting a car dealer. In the cam phaser replacement process, the mechanic needs to follow the diagnostic tests. It can take up to 10 to 20 hours to replace the cam phaser. 

Some First Hand Experiences Shared By Users In Different Communities

Our team conducted research across various online communities, forums, and subreddits to gather user comments and opinions on “what happens when cam phaser goes bad”.

User 1 says:

Had trouble with cold starts and a check engine light in my Volkswagen. Did some online research and thought it might be the cam phasers. I’m not too confident with mechanical stuff, so I had it checked at a service center. They replaced the cam phasers, and it’s been fine since.

User 2 says:

Had a weird issue where my BMW 328i would randomly lose power, then surge. Read on a BMW forum that it could be the cam phasers failing to adjust timing properly. Mechanic confirmed it; the phasers were intermittently sticking. Replaced them and it’s smooth now.

User 3 says:

Faced a rough idle in my Audi and the engine light popped up. A code reader showed a camshaft timing error. Suspected the cam phasers were failing to adjust the cam timing. A mechanic confirmed the phasers were not responding. Got them replaced, and the issue’s gone.

User 4 says:

Had a whining noise in my Accord and the VTEC system wasn’t engaging properly. Suspected it was due to the cam phasers not adjusting the camshaft position. My mechanic found the phasers were indeed faulty and replaced them. Performance is back to normal.

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