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Engine Controls - Basic Testing - 3.4L: Other Toyota Tacoma I

Testing & Diagnostics 5 illustrations ~1171 words

Compression

Warm engine to normal operating temperature before checking the compression. Check engine mechanical condition with a compression gauge, vacuum gauge, or engine analyzer. See engine analyzer manual for specific instructions. See COMPRESSION SPECIFICATIONS table.

WARNINGDO NOT use ignition switch during compression tests. Use a remote starter to crank engine. Fuel injectors on many models are triggered by ignition switch during cranking mode, which can create a fire hazard or contaminate the engine's oiling system.
ApplicationSpecification
Normal Compression Pressure174 psi (12.2 kg/cm 2 )
Minimum Compression Pressure145 psi (10.1 kg/cm 2 )
Maximum Variation Between Cylinders15 psi (1.1 kg/cm 2 )

COMPRESSION SPECIFICATIONS

Exhaust System Backpressure

  1. The exhaust system can be checked with a vacuum or pressure gauge. Remove HO2S sensor or air injection check valve (if equipped).
  2. Connect a 1-5 psi pressure gauge and operate engine at 2500 RPM. If exhaust system backpressure is greater than 2 psi, exhaust system or catalytic converter is plugged.
  3. If a vacuum gauge is used, connect vacuum gauge to intake manifold vacuum port and start engine. Observe vacuum gauge. Open throttle part way and hold it steady. If vacuum gauge reading slowly drops after stabilizing, check exhaust system for restriction.

FUEL SYSTEM

Basic diagnosis of fuel system should begin by checking fuel pump operation and fuel pressure.

WARNINGALWAYS relieve fuel pressure before disconnecting any fuel injection-related component. DO NOT allow fuel to contact engine or electrical components.

FUEL PRESSURE

Note. Vehicles use in-tank fuel pump.

  1. Ensure battery is fully charged and ignition is off. Disconnect negative battery cable.
  2. Note location for fuel pressure gauge installation. (Scheme 133) Fuel pressure gauge may be installed on fuel filter or on delivery pipe depending on model application.
  3. Place container under fuel filter or delivery pipe. Cover union bolt with shop towel. Slowly loosen union bolt to release fuel pressure.
  4. Remove union bolt and gaskets. Install Fuel Pressure Gauge (SST 09268-45012) using NEW gaskets. (Scheme 133) Tighten union bolt. Reconnect negative battery cable.
  5. Remove cover (if equipped) and install scan tool on data link connector No. 3. see scheme 1 Turn ignition on. DO NOT start engine.
  6. Turn scan tool on. Select ACTIVE TEST MODE on scan tool. Using scan tool manufacturer's instructions, activate fuel pump and note fuel pressure. Fuel pressure should be within specification. See «FUEL PUMP PERFORMANCE»(ref-22485-S00325557062001010300000) table. NOTE: Fuel pump may also be activated by connecting battery voltage to specified terminals on fuel pump. see scheme 2
  7. If fuel pressure exceeds specification, replace fuel pressure regulator. Fuel pressure regulator is located on the delivery pipe. If fuel pressure is less than specified, check for defective fuel lines, connections, fuel pump, fuel filter or fuel pressure regulator.
  8. Turn ignition off. Remove scan tool from data link connector No. 3. Reinstall cover (if equipped). Start engine and allow engine to idle.
  9. Disconnect and plug vacuum line at fuel pressure regulator. Note fuel pressure. Fuel pressure should be within specification. See «REGULATED FUEL PRESSURE»(ref-22485-S39023286642001010300000) table.
  10. Reconnect vacuum hose on fuel pressure regulator and note fuel pressure with engine idling. Fuel pressure should be within specification. See «REGULATED FUEL PRESSURE»(ref-22485-S39023286642001010300000) table.
  11. If fuel pressure is not within specification, check for defective vacuum hose or fuel pressure regulator. Shut engine off and note fuel pressure.
  12. Fuel pressure should hold at least 21 psi (1.5 kg/cm 2 ) for a minimum of 5 minutes. If fuel pressure does not hold as specified, check for defective fuel pump, fuel injector or fuel pressure regulator.
  13. Disconnect negative battery cable. Remove fuel pressure gauge. Reinstall union bolt using NEW gaskets. Tighten union bolt. Install negative battery cable. Recheck for fuel leaks.

Scheme 133

Scheme 133
Scheme 133

Note. For more information on checking fuel injectors and other fuel sub-systems, see SYSTEM/COMPONENT TESTS - 3.4L article.

ApplicationPressure psi (kg/cm 2 )
3.4L(1) 38-44 (2.7-3.1)
(1) Check fuel pressure with engine off and using scan tool connected to data link connector No. 3 with ignition on to activate fuel pump or by connecting battery voltage to terminals on electric fuel pump.
(1)Check fuel pressure with engine off and using scan tool connected to data link connector No. 3 with ignition on to activate fuel pump or by connecting battery voltage to terminals on electric fuel pump.

FUEL PUMP PERFORMANCE

Application Type TestedAt Idle W/Vacuum psi (kg/cm 2 )At Idle W/O Vacuum psi (kg/cm 2 )
3.4L33-38 (2.3-2.7)38-44 (2.7-3.1)

REGULATED FUEL PRESSURE

FUEL PUMP CONTROL CIRCUIT

Note. For information on testing relays and fuel system components, see SYSTEM/COMPONENT TESTS - 3.4L article. Relays may be identified by appropriate illustration in THEORY/OPERATION - 3.4L article. Vehicles are equipped with different combinations of fuel system electrical components. For complete wiring circuit of electrical components on a specific model, see appropriate wiring diagram in WIRING DIAGRAMS - 3.4L article.

Note. EFI main relay may also be referred to as EFI relay.

EFI Main Relay

The EFI fuse supplies constant battery voltage to EFI main relay. When ignition is turned on, voltage is supplied through IGN fuse to EFI main relay. EFI main relay is then energized and provides battery voltage to circuit opening relay, data link connector No. 1 and various other electrical components. The EFI main relay also provides battery voltage to +B terminal of Engine Control Module (ECM) when ignition is turned on.

Circuit Opening Relay

Circuit opening relay controls the fuel pump circuit. When EFI main relay is energized, EFI main relay provides battery voltage to one side of circuit opening relay. When engine is cranking, circuit opening relay receives a start signal which energizes circuit opening relay. Circuit opening relay then provides voltage to fuel pump for fuel pump operation. When start signal is released from circuit opening relay, the Engine Control Module (ECM) then controls the ground circuit for circuit opening relay at ECM terminal FC. Circuit opening relay then provides voltage to fuel pump for fuel pump operation.

IGNITION COIL RESISTANCE (DISTRIBUTORLESS IGNITION SYSTEM)

  1. Remove necessary components and disconnect electrical connector from ignition coil. Disconnect spark plug wire from ignition coil.
  2. Using ohmmeter, check ignition coil primary resistance between ignition coil positive (+) and negative (-) terminals. These are the terminals that electrical connector was installed on. (Scheme 134) Replace ignition coil if primary resistance is not within specification. See «DISTRIBUTORLESS TYPE IGNITION SYSTEM IGNITION COIL RESISTANCE»(ref-22485-S29251050082001010300000) table.
  3. To check ignition coil secondary resistance, remove ignition coil. Using ohmmeter, check ignition coil secondary resistance. (Scheme 135) Replace ignition coil if secondary resistance is not within specification. See «DISTRIBUTORLESS TYPE IGNITION SYSTEM IGNITION COIL RESISTANCE»(ref-22485-S29251050082001010300000) table. Reinstall ignition coil and electrical connector.

Scheme 134

Scheme 134
Scheme 134

Scheme 135

Scheme 135
Scheme 135
ApplicationPrimarySecondary
Cold (1).67-1.059300-16,000
Hot (2).85-1.2311,700-18,800
(1) Cold is with temperature of 14-122°F (-10-50°C). (2) Hot is with temperature of 122-212°F (50-100°C).
(1)Cold is with temperature of 14-122°F (-10-50°C).
(2)Hot is with temperature of 122-212°F (50-100°C).

DISTRIBUTORLESS TYPE IGNITION SYSTEM IGNITION COIL RESISTANCE - Ohms

CAMSHAFT POSITION SENSOR

  1. Disconnect electrical connector for camshaft position sensor. Electrical connector is located near upper radiator hose. (Scheme 136) Camshaft position sensor is located behind upper timing belt cover, near passenger's side camshaft sprocket.
  2. Using ohmmeter, check resistance between electrical terminals on electrical connector for camshaft position sensor. Replace camshaft position sensor if resistance is not within specification. See «CAMSHAFT POSITION SENSOR RESISTANCE»(ref-22485-S27925528642001010300000) table. Reinstall electrical connector for camshaft position sensor.
ApplicationOhms
Cold (1)835-1400
Hot (2)1060-1645
(1) Cold is with temperature of 14-122°F (-10-50°C). (2) Hot is with temperature of 122-212°F (50-100°C).
(1)Cold is with temperature of 14-122°F (-10-50°C).
(2)Hot is with temperature of 122-212°F (50-100°C).

CAMSHAFT POSITION SENSOR RESISTANCE

Scheme 136

Scheme 136
Scheme 136

CRANKSHAFT POSITION SENSOR

  1. Disconnect electrical connector from crankshaft position sensor. Crankshaft position sensor is located just above crankshaft pulley. (Scheme 137)
  2. Manufacturer recommends removing crankshaft position sensor before checking the resistance. Remove bolt and crankshaft position sensor.
  3. Using ohmmeter, check resistance between electrical terminals on crankshaft position sensor. Replace crankshaft position sensor if resistance is not within specification. See «DISTRIBUTORLESS TYPE IGNITION SYSTEM CRANKSHAFT POSITION SENSOR RESISTANCE»(ref-22485-S39644331312001010300000) table.
  4. Reinstall crankshaft position sensor. Install and tighten crankshaft position sensor bolt to 69 INCH lbs. (7.8 N.m). Reinstall electrical connector.
ApplicationOhms
Cold (1)1630-2740
Hot (2)2065-3225
(1) Cold is with temperature of 14-122°F (-10-50°C). (2) Hot is with temperature of 122-212°F (50-100°C).
(1)Cold is with temperature of 14-122°F (-10-50°C).
(2)Hot is with temperature of 122-212°F (50-100°C).

DISTRIBUTORLESS TYPE IGNITION SYSTEM CRANKSHAFT POSITION SENSOR RESISTANCE

Scheme 137

Scheme 137
Scheme 137

IDLE SPEED & IGNITION TIMING

Ensure idle speed and ignition timing are set to specification. For adjustment procedures, see ADJUSTMENTS - 3.4L article.

SUMMARY

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to TESTS W/CODES - 3.4L article. If no hard diagnostic trouble codes are found in self-diagnostics, proceed to TESTS W/O CODES - 3.4L article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.

More articles — Engine Controls - Basic Testing - 3.4L