5.4 Ford VCT;
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.
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.
Why did Ford use cam phasers with this engine?
Ford’s primary reason for using cam phasers was to increase the engine’s efficiency by reducing its pumping losses during part throttle cruise conditions. Basically, when the cams are retarded 20-40 degrees during part throttle engine operation, it takes less power to turn the engine over. This not only helps to increase the engine’s fuel efficiency, but an additional power benefit is also realized. The variable cam phasers allow the camshafts to be adjusted to the proper position for maximum power during wide-open throttle operation regardless of the current engine rpm. This results in an engine that makes more torque and horsepower and extends the high rpm power-band by an additional 800-1000 rpm.
Why can’t I just mechanically pin/lock the cam phasers?
While you certainly can do that, you are basically taking a step back in terms of making maximum power with your engine. If you lock the camshaft phasers in place, you will typically lose at least 20 hp or 20 ft. lbs. of torque, depending on the degree settings for your camshafts. The main reason so much power is lost is due to the fact that when you lose the ability to retard the cams at high engine speeds, there is a tremendous reduction in power producing airflow. The VCT (variable cam timing) technology is an incredible step forward in delivering both optimum torque and horsepower – a combination performance cam designers have always dreamed about. Why would you pass up the added performance this technology affords by locking it out?
