INTRODUCTION & ENGINE MECHANICAL FEATURES
The 2005 model year NPR/NQR truck, the 4HK1-TC inline 4 cylinder engine replaces the 4HE1-TC engine for advanced exhaust emission countries. The 4HK1-TC engine has been newly developed on the basis of previous 4HE1-TC engine, with additional features including the employment of four valve mechanism per a cylinder that are operated via a single camshaft, common rail fuel injection system, water-cooled exhaust gas re-circulation (EGR) system, and the change of combustion chamber form. The larger engine displacement and the common rail fuel injection system have resulted in an increase both in maximum output and torque, and met Euro 3 emission regulation standard. Most conspicuous items are listed below.
- Multi fuel injection type high-pressure common rail system and is made with Denso.
- Single overhead camshaft (OHC) with 4 valves per a cylinder.
- Electrical control EGR valve, water-cooled EGRcooler.
- Turbocharger with intercooler.
The base transmission is MYY for 4HK1-TCN low output engine, MZZ for 4HK1-TCS high output engine. The Smoother system is available for only MYY transmission.
To rotate the fuel supply pump with engine speed, idle gear has changed with three steps. The crankshaft gear (42 teeth) corresponds with the large diameter of idle gear A (72 teeth). The fuel supply pump gear (35 teeth) corresponds with the middle diameter of idle gear A (60 teeth). The idle gear B (61 teeth) corresponds with the small diameter of idle gear A (30 teeth).
To improve exhaust emission and engine output performance, four valve mechanism is newly adopted for 4HK1-TC engine. Note that the adjustment method of valve clearance has been changed from 4HK1-TC engine as following steps:
- Rotate the crankshaft to make the No.1 cylinder meet the compression top dead center (TDC). There are 2 marks stamped on the crank pulley. The mark (1) is used to bring the engine No.1 or No. 4 cylinder to TDC. The mark (2) is irrelevant. Do not use the mark (2).
- Loosen fully each adjusting screw (8) & (2) of the bridge and the rocker arm.
- Insert a 0.4mm (0.016in) thickness gauge between the tip of the rocker arm and bridge cap (5), and adjust the clearance with the adjusting screw (3) on the rocker arm, and then fix it with a lock nut (4).
- With a thickness gauge kept inserted, check that the adjusting screw (6) contacts the valve shaft end and the movement of the thickness gauge has become tight when the adjusting screw (6) on the bridge is tightened lightly.
- Check the valve shaft end on the opposite side floats or it contacts obliquely. In case of a floating or oblique contact, loosen a little the adjusting screw (6) on the bridge side and adjust so that the valve shaft ends on both sides get in contact properly. Bridge (8) & valve shaft end clearance less than 0.1 mm (0.004in).
- After the adjustment so that the end of the valves on both sides touch properly, tighten up the lock nut (7) on the bridge (8).
CYLINDER HEAD COVER & HEAD COVER CASE
Along with the employment of a common rail type fuel injection system, the head cover is split and housed in a newly introduced head cover case attached with an intermediate connector for the injector. The head cover case is so designed that it is secured individually to the cylinder head with four bolts, and further it is tightened together with the head cover with nine bolts. Accordingly, the head cover is removable individually regardless of the injector harness, thus enabling easy inspection and service including the valve clearance adjustment.
ENGINE CONTROL MODULE (ECM)
The engine control module (ECM) is located at inside of engine-side cover on the left via mounting bracket and is beside the engine. The ECM is made by Transtron. The ECM mainly controls the following:
- Fuel injection control
- Fuel timing control
- Exhaust gas recirculation (EGR) system control
- Preheating system control
- Exhaust brake control
- Power take off (PTO) control
- On-board diagnostics for engine control
The ECM constantly observes the information from various sensors. The ECM controls the systems that affect vehicle performance. The ECM performs the diagnostic function of the system. The ECM can recognize operational problems, alert the driver through the malfunction indicator lamp (MIL), and store diagnostic trouble code (DTC). DTC identify the system faults to aid the technician in making repair.
This diagnostic applies to internal microprocessor integrity conditions within the ECM. The electronically erasable programmable read only memory (EEPROM) memorize learning data and injector ID code data for engine control and communication with other control module.
Symbol “!” warns you of an electric shock hazard. To avoid shock and possible serious injury, DO NOT touch the terminals. When disconnecting the harness connector, always turn OFF the ignition switch or disconnect the battery cable.