2AZ-FE Toyota engine

Introduction

Toyota’s 2AZ-FE was a 2.4-litre four-cylinder petrol engine that was first introduced in Australia in the 2000 Toyota XR30 Tarago. The 2AZ-FE engine featured mass reduction measures such as an aluminium alloy cylinder block, plastic intake manifold and magnesium-alloy die-cast cylinder head cover. With a service weight of 110 kg, the 2AZ-FE engine was 50 kg lighter than the 5S-FE engine it replaced.

In 2006, an upgraded version of the 2AZ-FE engine was introduced for the XV40 Camry, XA40 RAV4 and XR50 Tarago. Changes for this updated engine included:

• A higher compression ratio of 9.8:1 (compared to 9.6:1);
• A more aggressive intake camshaft profile;
• Piston oil jets for better lubrication and lower operating temperatures;
• More efficient fuel injectors;
• A variable back-pressure muffler;
• New engine management software; and,
• A 6500 rpm redline.

It is this updated 2AZ-FE engine which was susceptible to excessive oil consumption (detailed below).

2AZ-FE cylinder block

The aluminium alloy cylinder block of the 2AZ-FE engine had 88.5 mm bores and a 96.0 mm stroke for a capacity of 2362 cc. The 2AZ-FE engine had cast iron liners which were manufactured so that their casting exteriors formed large, irregular surfaces (‘spiny type’) for better adhesion between the liners and the cylinder block.

Other features of the 2AZ-FE cylinder block included:

• Air passage holes in the crankshaft bearing area of the cylinder block for better air flow and reduced back pressure at the bottom of the pistons;
• Water jacket spacers which suppressed water flow in the centre of the jackets and guided the coolant around the cylinder bores;
• Oil filter and air conditioning compressor brackets that were integrated into the crankcase; and,
• The water pump swirl chamber and thermostat housing were also integrated into the cylinder block.

Balance shafts

The 2AZ-FE engine had twin counter rotating balance shafts that rotated twice for each rotation of the crankshaft to cancel secondary inertia forces. To cancel the inertial forces generated by the balance shaft itself, a second balance shaft rotated in the opposite direction. The drive for the no.1 balance shaft was driven via a gear on the number three crankshaft counter weight. To suppress noise and vibrations, the balance shafts were driven by resin gears.

Crankshaft, connecting rods and pistons

The 2AZ-FE engine had a forged steel crankshaft with five journals, eight balance weights and roll-finished pin and journal fillets. The 2AZ-FE’s crankshaft was offset by 10 mm to the thrust side of the cylinder bore centre line to reduce friction. According to Toyota, this design reduced fuel consumption by between one and three percent.

The connecting rods and caps were made of high-strength steel. To reduce mass, nut-less type plastic region tightening bolts and narrow connecting rod bearings were used.

The 2AZ-FE engine had aluminium alloy pistons. While the piston head had a taper squish shape, the piston skirt was coated with resin to reduce frictional losses. For the updated, post-2006 2AZ-FE engine, the cylinder block contained oil jets for lubricating and cooling the pistons; these jets contained a check valve to prevent oil from being fed when oil pressure was low and to prevent overall oil pressure in the engine from dropping.

Cylinder head

The 2AZ-FE engine had an aluminium alloy cylinder head which was mounted upon a steel-laminate type head gasket; to increase the sealing surface, a shim was used around the cylinder bore. To reduce mass, the 2AZ-FE engine had a magnesium alloy die-cast cylinder head cover.

Camshafts

The 2AZ-FE engine had double overhead camshafts (DOHC) that were driven by a roller chain which had an 8 mm pitch and was lubricated by an oil jet. The chain tensioner used a spring and oil pressure to maintain chain tension; it also used a ratchet type non-return mechanism.

Valves

The 2AZ-FE engine had four valves per cylinder (two intake and two exhaust) that were positioned such that the included valve angle was 27.5 degrees. The intake valves each had a diameter of 34.0 mm, while exhaust valve diameter was 29.5 mm; for both intake and exhaust valves, valve lift was 8.0 mm. Furthermore, the 2AZ-FE engine used shimless type valve lifters that provided a large cam contact surface.

Variable Valve Timing-intelligent (VVT-i)

The 2AZ-FE engine featured Toyota’s ‘Variable Valve Timing – intelligent’ (VVT-i) system which varied intake valve timing according to driving conditions (based engine speed, vehicle speed, intake air mass and flow, throttle position and engine coolant temperature). The ECM used signals from the camshaft position sensor and crankshaft position sensor to detect the actual valve timing, thereby providing feedback control to achieve the target valve timing.

For the original 2AZ-FE engine, intake valve overlap ranged from -1 to 49 degrees relative to crankshaft angle, intake duration was 236 degrees and exhaust duration was 228 degrees.

For the updated, post-2006 2AZ-FE engine, intake valve overlap ranged from 6 to 46 degrees, intake duration was 248 degrees and exhaust duration was 228 degrees.
The VVT-i system used:

• A camshaft timing oil control valve that was mounted adjacent to the inlet camshaft gear wheel; and,
• A VVT-i controller which had a four-bladed vane and was built onto the inlet camshaft timing gear.

The camshaft timing oil control valve was a spool-type valve that was controlled – via the ECU – by a coil and plunger; the ECU could signal ‘advance’, ‘hold’ or ‘retard’. When the ECU required a change in intake valve timing, it signalled the oil control valve to provide oil pressure to either the ‘advance’ or ‘retard’ side of the four vane chambers.

Inlet cam timing was set to the maximum ‘retard’ position for engine start-up, operation at low engine temperature, idle and engine shutdown. Furthermore, a locking pin in the controller locked the camshaft timing in the maximum ‘retard’ position for engine start-up and immediately after start-up (until oil pressure is established) to prevent any knocking noise.

Intake and throttle

The 2AZ-FE engine had a plastic intake manifold and, within the air intake chamber, a resonator to utilise intake pulsations to improve torque at medium engine speeds. The 2AZ-FE engine used a plug-in type mass air flow meter which allowed a portion of the intake air to flow through the detection area so that air mass and flow rate could be measured. The mass air flow meter also had an integrated intake air temperature sensor.

The 2AZ-FE engine had a link-less type ‘Electronic Throttle Control System – intelligent’ (ETCS-i) which controlled the throttle valve opening according to the amount of accelerator pedal effort and engine condition.

Injection and ignition

The 2AZ-FE engine had an L-type sequential fuel injection (SFI) system which used twelve-hole injectors and provided two types of fuel injection:

• A synchronous injection in which corrections based on the signals from the sensors were added to the basic injection timing so that injection always occurred at the same position; and,
• A non-synchronous injection in which injection was influenced by signals from sensors (regardless of the crankshaft angle).

The 2AZ-FE engine had Toyota’s ‘Electronic Spark Advance’ (ESA) which selected optimal ignition timing in accordance with inputs from sensors. The default ignition timing was set to 5 degrees before top dead centre (BTDC).

The 2AZ-FE engine had pentroof type combustion chambers – which incorporated a slant-squish design – and iridium-tipped spark plugs. The original 2AZ-FE engine had a compression ratio of 9.6:1; for the updated, post-2006 2AZ-FE engine, the compression ratio was 9.8:1. The firing order for the 2AZ-FE was 1-3-4-2.

Exhaust

The 2AZ-FE engine had a stainless steel exhaust manifold and an ultra thin-wall, high-cell ceramic type three-way catalytic converter (TWC). Furthermore, the two-way exhaust system reduced back pressure by opening and closing a variable valve within the main muffler. The valve opened steplessly according to the operating condition of the engine, enabling quieter operation at lower engine speeds and reduced back pressure at higher engine speeds.

2AZ-FE oil consumption

The 2AZ-FE engine is susceptible to excessive oil consumption due to oil getting past the piston rings and into the combustion chamber. There have been reports of excessive oil consumption for 2AZ-FE powered Toyota vehicles with mileages as low as 70,000 kms, though it is more commonly experienced from 100,000 to 120,000 kms.

Technical Service Bulletin: TSB #0094-11

In August 2011, Toyota issued the TSB #0094-11 which noted that 2006 to 2011 model year vehicles with the 2AZ-FE engine may experience excessive oil consumption. In TSB #0094-11, Toyota prescribed an oil consumption test in which oil consumption would be considered excessive if it exceeded more than 1 quart (approximately 1 litre) of oil for 1200 miles (1930 km) of normal driving. If this threshold was exceeded, the piston assembly (i.e. pistons and piston rings) would be replaced – this required the engine to be removed from the vehicle.

Limited Service Campaign (LSC) ZE7

In January 2015, Toyota USA initiated a ‘Warranty Enhancement Program’ known as Limited Service Campaign (LSC) ZE7 for the 2AZ-FE engine. As part of this program,

• Toyota informed owners that they could seek reimbursement for the cost of previous repairs to address excessive oil consumption;
• Owners were advised that they could have an engine oil consumption test to determine if their vehicle was experiencing excessive oil consumption. It is understood that the threshold for this test was the same as described in TSB #0094-11 (i.e. 1 quart per 1200 miles); and,
• For vehicles with excessive oil consumption, the pistons would be replaced at no cost to the owner.

As part of the warranty enhancement, the ‘Primary Coverage’ period lasted until October 31, 2016, regardless of mileage. Once the ‘Primary Coverage’ period ended, a ‘Secondary Coverage’ period commenced and was applicable from ten (10) years from the date of first use or 150,000 miles (241,350 kms), whichever occurred first.