Compression
Check engine mechanical condition with a compression gauge, vacuum gauge, or engine analyzer. See engine analyzer manual for specific instructions.
| WARNING | DO 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. |
| Application | Psi (kg/cm 2 ) |
|---|---|
| Normal Compression Pressure | 178 (12.5) |
| Minimum Compression Pressure | 128 (9.0) |
| Maximum Variation Between Cylinders | 14 (1.0) |
COMPRESSION SPECIFICATIONS
FUEL SYSTEM
Basic diagnosis of fuel system should begin by checking fuel pump operation and fuel pressure.
| WARNING | ALWAYS relieve fuel pressure before disconnecting any fuel injection-related component. DO NOT allow fuel to contact engine or electrical components. |
FUEL PRESSURE
Note. In-tank fuel pump is used. Fuel pump contains internal relief valve and check valve.
- Ensure battery is fully charged and ignition is off. Disconnect negative battery cable.
- Note location of fuel pressure gauge installation. (Scheme 3) Place container under delivery pipe or fuel filter. Cover union bolt with shop towel. Slowly loosen union bolt to relieve fuel pressure.
- Remove union bolt and gaskets. Install Fuel Pressure Gauge (SST 09268-45012) using NEW gaskets. (Scheme 3) Tighten union bolt. Reconnect negative battery cable.
- Install scan tester on data link connector No. 3. see scheme 1 Using scan tester manufacturer's instructions, activate electric fuel pump and note fuel pressure. Fuel pressure should be within specification. See «FUEL PUMP PERFORMANCE»(ref-21581-S13445767192001010300000) table. NOTE: Fuel pump may also be activated by connecting battery voltage to specified terminals on fuel pump. see scheme 2
- If fuel pressure exceeds specification, replace fuel pressure regulator. If fuel pressure is less than specified, check for defective fuel lines, connections, fuel pump, fuel filter, fuel pressure regulator or fuel pressure control Vacuum Switching Valve (VSV) if equipped.
- Remove scan tester from data link connector No. 3. Start engine and allow to idle. Disconnect and plug vacuum line at fuel pressure regulator. Note fuel pressure.
- Reconnect vacuum hose on fuel pressure regulator and note fuel pressure. Fuel pressure should be within specification. See the «REGULATED FUEL PRESSURE»(ref-21581-S34302282642001010300000) table.
- If fuel pressure is not within specification, check for defective vacuum hose or fuel pressure regulator. Shut engine off and note fuel pressure.
- 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.
- Disconnect negative battery cable. Remove fuel pressure gauge. Reinstall union bolt using NEW gaskets. Tighten union bolt. Install negative battery cable.
Scheme 3
Note. For more information on checking fuel injectors and other fuel sub-systems, see the SYSTEM/COMPONENT TESTS article.
| Application | Psi (kg/cm 2 ) |
|---|---|
| 4-Cylinder | 38-44 (2.7-3.1) |
FUEL PUMP PERFORMANCE
| Application | At Idle W/Vacuum | At Idle W/O Vacuum |
|---|---|---|
| T100 | 31-37 (2.2-2.6) | 38-44 (2.7-3.1) |
REGULATED FUEL PRESSURE
FUEL PUMP CONTROL CIRCUIT
Note. For information on testing relays and fuel system components, see the SYSTEM/COMPONENT TESTS article. Relays may be identified by illustration in the THEORY/OPERATION - 2.7L article. Vehicles are equipped with different combinations of fuel system electrical components. For complete wiring circuit of electrical components on a specific model, see wiring diagram in the WIRING DIAGRAMS article.
EFI Main Relay
The EFI fuse supplies constant battery voltage to EFI main relay. When EFI main relay is energized by ignition switch, EFI main relay provides battery voltage to circuit opening relay (some models), data link connector No. 1 and various other electrical components. The EFI main relay may also provide battery voltage to +B terminal of ECM when ignition is turned on. The EFI main relay is located in engine compartment relay box.
Circuit Opening Relay
Circuit opening relay controls fuel pump circuit. When EFI main relay is energized, EFI main relay provides battery voltage to 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. When start signal is released from circuit opening relay, the circuit opening relay ground circuit is controlled at Engine Control Module (ECM) terminal FC.
CRANKSHAFT POSITION SENSOR
- Manufacturer recommends removing crankshaft position sensor before checking the resistance. Disconnect negative battery cable. Remove lower engine cover. Remove alternator and mounting bracket for access to crankshaft position sensor. Crankshaft position sensor is located on front of engine, near crankshaft pulley. (Scheme 4)
- Disconnect electrical connector at crankshaft position sensor. Remove bolts, crankshaft position sensor and "O" ring.
- Using ohmmeter, measure resistance between terminals NE- and NE+ on crankshaft position sensor. (Scheme 4) Replace crankshaft position sensor if resistance is not 1630-2740 ohms at 14-122°F (-10-50°C) and 2065-3225 ohms at 122-212°F (50-100°C).
- Reinstall crankshaft position sensor using NEW "O" ring. Apply engine oil to "O" ring before installing crankshaft position sensor. Install and tighten crankshaft position sensor bolts to 75 INCH lbs. (8.5 N.m). Reinstall remaining components.
Scheme 4
IGNITION COIL RESISTANCE
- Disconnect wiring from ignition coil so ignition coil is isolated from system. Using ohmmeter, check ignition coil primary resistance between ignition coil positive (+) and negative (-) terminals. (Scheme 5)
- Check ignition coil secondary resistance between ignition coil positive (+) terminal and high tension terminal (coil wire tower). (Scheme 6) Replace ignition coil if resistance is not within specification. See the «IGNITION COIL RESISTANCE»(ref-21581-S07027362972001010300000) table.
| Application | Primary | Secondary |
|---|---|---|
| Cold (1) | .36-.55 | 9000-15,400 |
| Hot (2) | .45-.65 | 11,400-18,100 |
| (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). |
IGNITION COIL RESISTANCE
Scheme 5
Scheme 6
PICK-UP COIL RESISTANCE
Disconnect electrical connector on distributor and note pick-up coil terminal identification on the distributor. (Scheme 7) Using ohmmeter, measure resistance between specified terminals. See PICK-UP COIL RESISTANCE SPECIFICATIONS table. Replace distributor assembly if pick-up coil resistance is not within specification.
| Application | Pick-Up Coil Terminals | Ohms |
|---|---|---|
| Cold (1) | G+ & G | 185-275 |
| Hot (2) | G+ & G | 240-325 |
| (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). |
PICK-UP COIL RESISTANCE SPECIFICATIONS
Scheme 7
PICK-UP COIL AIR GAP
- Using non-magnetic feeler gauge, check air gap between signal rotor and pick-up coil projection. (Scheme 8)
- Replace distributor assembly if pick-up coil air gap is not within specification. See «PICK-UP COIL AIR GAP SPECIFICATIONS»(ref-21581-S14342941522001010300000) table.
| Application | In. (mm) |
|---|---|
| 4-Cyl. 2.7L | .008-.016 (.20-.40) |
PICK-UP COIL AIR GAP SPECIFICATIONS
Scheme 8
IDLE SPEED & IGNITION TIMING
Ensure idle speed and ignition timing are set to specification. For adjustment procedures, see the ADJUSTMENTS - 2.7L article.
SUMMARY
If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to the TESTS W/CODES article. If no hard diagnostic trouble codes are found in self-diagnostics, proceed to the TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.