Ford 5.4L Variable Cam Timing
The Ford 5.4L Triton 3 valve engine is a wonderful masterpiece that many hate and do not understand. Many are confused about the rattling sounds they hear on light acceleration and many people have been told it is the phasers. What is a phaser?, What does it do? I get into the details of how the 5.4L's variable cam timing system works. This is a very detailed technical article so feel free to bookmark and share.
This article is mainly written with the 5.4L truck engine in mind, but also applies to the 4.6L Ford modular 3 valve engine used in trucks, vans, and cars.
Here is a quick reference if you are unfamiliar with Ford Triton line of engines; there are three main variations 97-up. The 5.4L 2 valve used between 1997-2004 only has a total of 16 valves for all cylinders but does not have variable valve timing system. The 5.4L 3 valve used from 2004-2010 with variable valve timing outperforms that engine in every way, producing 15ft.lbs more torque and around more 40hp. There is also a 5.4L 4v used in Navigators but it also does not use variable valve timing.
From this point on, I will be using VCT to refer to variable cam timing. VCT is a way to juggle both the need for high torque and the need for engine efficiency. On some vehicles, including the 5.4L 3 Valve, VCT is controlled so that it also replaces the EGR system. With the use of a phaser, the camshaft is allowed to move independently of the timing sprocket. In this manner, VCT allows the engine to advance or retard the camshaft timing. The term 'Advance' means to make the valve open sooner, and to "Retard" would be to make the valve open later. Ford uses several types of systems on different applications to perform these functions, and the type of setup they use dramatically effect the advantages gained. The four main types of variable valve timing Ford uses are:
IPS (intake phase shifting) - VCT only effects the intake camshaft
EPS (exhaust phase shifting) - VCT only effects the exhaust camshaft
DIPS (dual independent phase shifting) - VCT can control both intake and exhaust camshafts independently
DEPS (dual equal phase shifting) - VCT can control intake and exhaust, but only equally together
Since this is a lesson on the 5.4L 3 valve Triton engine, we will only discuss the DEPS system. In this engine, there are two camshafts. Each camshaft controls exhaust and intake valves on a separate bank. The VCT system uses a phaser to control the whole camshaft, which in turn retards or advances both the intake and exhaust valves simultaneously on each bank. It can, however, control each bank independently. The way this engine is tuned is that an advanced camshaft is best for high torque, high power situations and a retarded camshaft is best for low torque, low emission, cruising situations.
Advantages of VCT DEPS
Any VCT system that can phase at least the exhaust valve timing can eliminate the need for a EGR valve. On the system in the ford 5.4 liter, when the PCM determines it necessary, the VCT system can retard the camshaft timing to decrease the amount of clean air that may enter the combustion chamber from the intake valve by opening it later while simultaneously leaving the exhaust valve open longer during the intake stroke to allow more exhaust gases to reinsert into the combustion chamber. Exhaust gases are inert and do not contain oxygen so they neither increase or decrease the fuel mixture ratio, but merely act as a useless space filler. By partially filling the cylinder with this inert gas, less oxygen can enter the cylinder and in turn less fuel is needed to maintain the desired fuel ratio. This less powerful explosion reduces combustion chamber temperature which then effectively reduces harmful NoX emissions. Reduction of NoX emissions is the primary purpose of an EGR system. By phasing the cams, we can effectively do the job of a EGR valve so there is no longer a need for one. This process is known as scavenging. That is the whole purpose of the variable cam timing on the 5.4L Triton engine.
Components of the VCT System
The PCM controls the timing of the camshafts by the use of a VCT solenoid that allows oil pressure to enter the camshaft phaser. The VCT solenoid is essentially an electronically controlled spool valve. The PCM controls this spool valve by pulse width modulation, or abbreviated as PWM (see Electrical Dictionary.) Depending on the position of the spool valve, it allows oil pressure to enter the phaser to advance or retard camshaft timing. The PCM can modulate timing several times per second on to command timing changes. Since the actual process after the VCT solenoids is mechanical and hydraulic, worn or damaged parts and low oil pressure can slow this process down. The default off position allows oil into the advance side of the phaser, helping spring pressure hold the phasers completely advanced.
The phaser consists of a outer component that is attached to the sprocket and mechanically linked by a chain, an inner component which is attached by a banjo bolt and the locating pin to the camshaft, and a center vane assembly that allows the inside unit to turn away from the outside unit. The phaser gets it's oil supply directly from the center of the camshaft by a banjo bolt. This oil supply actually travels through the block, into the camshaft front bearing, through the camshaft, then finally into the phaser.
There are two main pins on this phaser design. One of those pins is a stationary locating pin on the inside component of the phaser unit. It sits between the phaser and the camshaft preventing the camshaft from moving independently from the inner component of the phaser. The second one is a locking pin which prevents unintended movement and is located inside of the phaser unit. This pin prevents the camshaft sprocket from rotating independently from the sprocket whenever the engine is started. Oil pressure is fed to the pin by the VCT solenoid when commanded which releases the phaser and allows VCT operation to begin. There are many enabling conditions that need to be met before this process starts. Two operating variables is that engine oil temperature must be normal and engine speed must be above 800RPM, otherwise the system is inactive and should be defaulted at idle to the full advance position.
The phaser front has the pickups for the magnetic cam position sensor. This part of the phaser has the return spring build in beneath and also spins directly with the camshaft so that engine always knows how the VCT is effecting the timing. For those wishing to see the VCT phaser disassembled can read this Ford 5.4L Triton VCT Phaser Breakdown The return spring assists the phaser to return back to the default full advanced position.
Controlling the VCT System
On this system, when the PCM sends the PWM signal of 0%, or simply off, the spool valve is moved so that the oil is forced to fully advance the timing. Fully advanced is simply normal or rather no change to the timing in this application. As the PCM sends a PWM signal of more than 0%, the spool valve moves and starts to allow the pressure to equalize between the advance and retard sides of the phaser. As the PWM signal increases, oil is allowed to pressurize the retard side of the vanes, forcing the phaser to turn counter clockwise, meaning cam timing retards. When the solenoid is commanded at 0%, the locking pin should remain engaged. As the solenoid commands more duty cycle the locking pin will release from oil pressure. Simply unplugging the VCT solenoid will default the spool valve in the fully advanced position, or OFF. If there are any detected faults in the system, the PCM will keep the solenoid off so the phaser stays in the default locked position.
VCT Common Failure Points
The locking pins are prone to failure and unintentionally allow the camshaft sprocket to rotate separately from the chain when not currently in active use. As the camshaft turns, it fights against the valve spring force causing the phaser to jump back and forth at lower RPMs if oil pressure is insufficient enough to hold it. This causes a rattle. These excessive forces on the chain could also lead to timing tensioner, chain, or guide breakage. (These failures is my personal explanation of what I have noticed, I could be wrong.) As the phaser jumps back and forth, it forces oil backwards into the camshaft and front camshaft bearing and cap. Debris can get stuck in this process and can lead to repeat phaser failure as well as fatal camshaft damage.
Another type is failure is the roll pins holding the cam position pickups to the phaser. Broken roll pins can cause the cam sensor reluctance pickups to become out of place and allowing the spring to push the end off into the cam sensor. Other failures would be from oil contamination, VCT solenoid failures, and main oil system problems. These engines have a tendency to leak pressurized oil out of the center of the oil pump which leads to lower system pressure. A VCT system failure could be the result of the oil pump being unable to hold a minimum of 26psi at a very hot idle or a possibly clogged pump sump screen.
Diagnosis of VCT System
IDS, or Integrated Diagnostic Software or equivilent, is required to monitor the PIDs or control output states necessary to properly diagnose this system. Failure or disabling of this system can result in noticeable power loss, efficiency loss (less MPG!!) and possible engine damage. Locking the VCT system in full advance will certainly result in higher emissions, lower fuel efficiency, higher combustion temperatures, and NO EXTRA POWER since the engine already advances the timing when it is needed BUT usually a good idea for high mileage vehicles or to just eliminate future issues. The PIDs you will want to monitor are VCTFAULT, VCTERROR1, VCTERROR2, VCTDC1, VCTDC2. Lockers or limiters may need to be installed if aftermarket aggressive camshafts are to be used otherwise piston to valve damage will occur. Base oil pressure should be checked as well.
The ERROR pids should read near zero at all times, but they will jump around a little bit. As long as they return to near zero fairly quickly during throttle changes or commands you generally are good to go. The VCTDC pids show the commanded duty cycle of the VCT solenoids. The VCT ADVANCE pids show the current command cam position.
Those who have a rough idle, rattling noise under light load at 1500 rpm, or diesel sounding running rough condition after returning to a hot idle, you should replace the VCT solenoids first and read about the Ford Technical Service bulletin related to VCT Solenoids. Replacing these components can be a tedious task on certain model years, just because removing the valve cover is a pain. If your issue is not resolved, the issue is most likely going to be oil pressure related. I would suggest replacing the timing chains, timing components, and a oil pump - and possibly installing a VCT lockout kit. I wrote an article that provides step by step instructions to replace the timing chain, tensioners, guides, and phasers on the 5.4L 3valve engine. The article lists all the parts you will need, where to get them, and any specialty tools required for Changing 5.4L Phasers and Timing Chain
For those interested, I have compiled a list of Ford 5.4L Triton Common Problems.