General information
The VTEC system was developed by Honda specialists to provide dynamic control of valve timing and valve opening. Engines equipped with this system are marked with the VTEC inscription molded on the cylinder head cover. The corresponding engine series number (F23A1 or F23A4) is stamped on the side of the block facing the radiator.
The difference between engines equipped with the VTEC system and the basic version consists exclusively in the principle of controlling the valve timing and the features of the valve mechanism. The design of the reduced engine block kit, the lubrication and cooling system organization scheme remain the same, as well as the list, design and location of attachments.
The onboard processor of the engine management system of VTEC-equipped models is capable of adjusting the moments of operation and the degree of opening of the intake valves by using camshaft cams of different sizes and shapes. Depending on the data received from the information sensor, the processor either turns the system on or off.
The operating order of both types of VTEC systems is determined by the following initial parameters:
- a) Engine speed (rpm);
- b) Vehicle speed (mph);
- c) Throttle Position Sensor (TPS) Output Signal;
- d) Current engine load determined by the absolute pressure sensor (MAP) readings;
- e) Coolant temperature.
The camshaft is equipped with three cams for driving each of the engine's intake valves, which differ from each other in profile shape and lift height, which determine the duration and amount of opening of the corresponding valves.
At low engine speeds, the secondary intake valves are operated by their own camshaft cams, which have a very small lift and a pointed shape (i.e. the valves, in comparison with the primary ones, open only slightly and for a very short time), keeping the atomized fuel from consolidating inside the cylinder head. At the same time, a good lower torque with a high response speed is developed, which determines excellent traction characteristics and high throttle response of the car. The primary cams function in normal mode, creating swirls of the combustible mixture in the combustion chambers.
If there is a need to increase the engine output, the secondary rocker arms are locked through the intermediate ones with the primary special synchronizing pistons. The synchronizing pistons have a hydraulic drive with electronic control. When the rocker arms are locked, both intake valves begin to open in the same mode, and the degree and duration of their opening are determined by the shape of the intermediate rocker arm cam and have an increased value.
Note: The secondary rocker arms are no longer in contact with their own cams until the system is disengaged, at which point both valves open to their full height and duration, providing increased engine speed and power.
Checking the status of components
Note: Checking some of the VTEC components requires removal of the rocker arm assembly (see Section Removal, condition check and installation of rocker arm assembly).
VTEC Lock-Up Control Solenoid Valve
Note: Failure of the VTEC solenoid valve to function will cause a fault code to be stored in the self-diagnostic unit memory and the Check Engine light to come on (see Chapter Engine management).
The most common cause of VTEC malfunction is a faulty solenoid valve or its filter. Regularly changing the engine oil and filter will help avoid annoying failures.
1. The VTEC lock-up control solenoid valve is located on the right side of the rear cylinder head (on the side of the rear bulkhead of the engine compartment).
2. Check for conductivity between the electromagnetic valve connector and the body ground. There should be a resistance of 14÷30 Ohm; otherwise the VTEC solenoid valve must be replaced.
3. With the ignition off, disconnect the wiring harness connector from the VTEC pressure switch and check for continuity between the two terminals of the switch on the VTEC solenoid. There should be continuity, otherwise replace the switch. 4. Turn the ignition on and measure the voltage between the blue/black wire terminal of the pressure switch and ground. The desired value is about 12 V, otherwise check the wire between the connector and the PCM for opens or shorts to ground.
5. Without turning off the ignition, measure the voltage between the terminals of the pressure sensor-switch wiring harness connector. There should be a voltage of 12 V, otherwise, you should repair the break in the brown-black wire.
6. Remove the solenoid valve and manually check the free movement of its plunger. When installing the valve back, do not forget to replace the sealing gasket.
7. Completely remove the solenoid valve assembly from the cylinder head and check the condition of the sealing gasket and the filter patency. Clean the assembly and install it in place, after replacing the sealing gasket.
Note: A blocked mesh filter is the most likely cause of VTEC system failure.
Rocker arms
1. Bring the piston of the first cylinder to the TDC position of the end of the compression stroke (see Section Bringing the piston of the first cylinder to the top dead center (TDC) position). Remove the cylinder head cover (see Section Removal and installation the cylinder head cover).
2. Press your finger on the intermediate rocker arm of the first cylinder intake valve set - it should move independently of the primary and secondary rocker arms of the assembly. Proceeding in the same order, check the proper functioning of the intake valve rocker arms of the remaining cylinders (the corresponding pistons are moved to the TDC positions).
Valve clearance correctors
1. The assemblies of four correctors are placed in special pockets in the engine cylinder head.
2. Remove each of the correctors from the cylinder head separately.
3. Check the correctors for proper operation by pressing the plungers with your finger. The plunger should move with slight resistance, gradually increasing it as it goes deeper, otherwise replace the defective assembly.
Synchronizing assemblies
1. After removing and disassembling the rocker arm assemblies (see Section Removal, condition check and installation of rocker arm assembly), also remove the components of the synchronization nodes (see below).
VTEC Timing Assembly Components:
- a) Primary valve drive rocker arm (primary rocker arm);
- b) Secondary valve drive rocker arm (secondary rocker arm);
- c) Intermediate rocker arm;
- d) Synchronizing piston A;
- e) Synchronizing piston B;
- f) Distribution piston.
2. Check the condition of the distribution spring. Make sure it is not broken or sagging. Replace it if necessary.
3. Check all other components (rocker arms and synchronizing pistons) for signs of wear, abrasions, scoring, traces of overheating and other defects. Replace defective parts. Remove the oil spray jet from the third camshaft holder, clean it and install it in place (engines without VTEC). 4. Assembly is carried out in the reverse order of dismantling the components.
Note: Assemble the components of each cylinder assembly together, secure them with a rubber bandage, and only then install them on the axle (see Section Removal, condition check and installation of rocker arm assembly).