For 1990-2009 cars

### Cylinder Head and Gasket

The cylinder head is made up of an aluminum alloy. The cylinder head uses crossflow intake and exhaust ports. A spark plug is located on the exhaust side of each combustion chamber.

### Crankshaft

The crankshaft has 8 integral weights which are cast with it for balancing. Oil holes run through the center of the crankshaft to supply oil to the connecting rods, the bearings, the pistons, and the other components. The end thrust load is taken by the thrust washers installed at the center journal.

### Timing Belt

Important: This engine design is what is commonly referred to as an interference type engine. Meaning in the event of a timing belt failure, the crankshaft and pistons would continue to rotate and camshafts and valves would remain stationary. Under certain circumstances, it would cause damage to the pistons, valves and the cylinder head itself. Refer to the Maintenance Schedule and perform the timing belt inspections and replacements at the intervals that are suggested.

The timing belt coordinates the crankshaft and the camshaft and keeps them synchronized. The timing belt also turns the coolant pump. The timing belt and the pulleys are toothed so that there is no slippage between them. There is a tension pulley that maintains the correct timing belt tension. The timing belt is made of a tough reinforced rubber similar to that used on the serpentine accessory drive belt. The timing belt requires no lubrication.

### Oil Pump

The oil pump draws engine oil from the oil pan and feeds it under pressure to the various parts of the engine. An oil strainer is mounted before the inlet of the oil pump to remove impurities which could clog or damage the oil pump or the other engine components. When the drive gear rotates, the driven gear rotates. This causes the space between the gears to open and narrow constantly, pulling oil in from the oil pan when the space opens and pumping the oil out to the engine as it narrows.

At high engine speeds, the oil pump supplies a much higher amount of oil than required for lubrication of the engine. The oil pressure regulator prevents too much oil from entering the engine lubrication passages. During normal oil supply, a coil spring and a valve keep the bypass closed, directing all of the oil pumped to the engine. When the amount of oil being pumped increases, the pressure becomes high enough to overcome the force of the spring. This opens the valve of the oil pressure regulator, allowing the excess oil to flow through the valve and drain back to the oil pan.

### Oil Pan

The oil pan is mounted to the bottom of the cylinder block. The oil pan houses the crankcase and is made of aluminum.

Engine oil is pumped from the oil pan by the oil pump. After the oil passes through the oil filter, the oil is fed through 2 paths to lubricate the cylinder block and the cylinder head. In one path, the oil is pumped through the oil passages in the crankshaft to the connecting rods, then to the pistons and the cylinders in the cylinder block. The oil then drains back into the oil pan. In the 2nd path, the oil is pumped through the oil passages to the camshaft. The oil passes through the internal passageways in the camshafts to lubricate the valve assemblies in the cylinder head before draining back into the oil pan.

### Exhaust Manifold

A single 4-port, rear-takedown exhaust manifold is used with this engine. The exhaust manifold is designed to direct the escaping exhaust gases out of the combustion chambers with a minimum of back pressure. The oxygen sensor (O2S) is mounted to the exhaust manifold.

### Intake Manifold

The intake manifold has 4 independent long ports and uses inertial supercharging to improve engine torque at low and moderate speeds. The plenum is attached to the intake manifold.

### Camshafts

This engine is a dual over head camshaft (DOHC) type, which means there are 2 camshafts. One camshaft operates the intake valves, and the other camshaft operates the exhaust valves. The camshafts sit in journals in the cylinder head on the top of the engine. They are held in place by camshaft caps. The camshaft journals of the cylinder head are drilled for oil passages. Engine oil travels to the camshafts under pressure where it lubricates each camshaft journal. The oil returns to the oil pan through drain holes in the cylinder head. The camshaft lobes are machined into the solid camshaft to open and close the intake and exhaust valves precisely the correct amount at the correct time. The camshaft lobes are oiled by splash action from pressurized oil escaping from the camshaft journals.

### Exhaust Gas Recirculation (EGR) Valve

The exhaust gas recirculation (EGR) system is used to lower oxides of nitrogen (NOx) emission levels caused by high combustion temperatures. The main element of the system is the EGR valve which is operated electrically by the engine control module (ECM).

The EGR valve feeds small amounts of exhaust gas into the intake manifold to decrease the combustion temperature. The amount of exhaust gas recirculated is controlled by variations in electrical signal and exhaust back pressure. If too much exhaust gas enters, combustion will not take place. For this reason, very little exhaust gas is allowed to pass through the valve, especially at idle.

The EGR valve is controlled precisely by the ECM according to various operating conditions of the engine.