Compression
Check engine mechanical condition with a compression gauge, vacuum gauge, or an engine analyzer. See engine analyzer manual for specific instructions.
| WARNING | DO NOT use ignition switch during compression tests on fuel injected vehicles. 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 (1) | Psi (kg/cm 2 ) | |
|---|---|---|
| Compression Pressure | ||
| 3.0L (VIN J) | 185 psi (13.0 kg/cm 2 ) | |
| 3.0L (VIN K) | 156 psi (10.9 kg/cm 2 ) | |
| 3.0L (VIN H) | 171 psi (12.0 kg/cm 2 ) | |
| Maximum Variation Between Cylinders | 14 psi (1.0 kg/cm 2 ) | |
| (1) See ENGINE/VIN ID article in this section for VIN information. | ||
| (1) | See ENGINE/VIN ID article in this section for VIN information. |
COMPRESSION SPECIFICATIONS
Exhaust System Backpressure
Exhaust system can be checked with a vacuum or pressure gauge. Remove O2 sensor or air injection check valve (if equipped). Connect a 0-5 psi pressure gauge and run engine at 2500 RPM. If exhaust system backpressure is greater than 1 3/4 - 2 psi, exhaust system or catalytic converter is plugged.
If using a vacuum gauge, connect vacuum gauge hose to intake manifold vacuum port and start engine. Observe vacuum gauge. Open throttle part way and hold steady. If vacuum gauge reading slowly drops after stabilizing, exhaust system should be checked for a restriction.
FUEL SYSTEM
| WARNING | ALWAYS relieve fuel pressure before disconnecting any fuel injection-related component. DO NOT allow fuel to contact engine or electrical components. |
Relieving Fuel Pressure
- On Diamante, disconnect fuel pump harness connector at fuel tank from underneath vehicle. On Stealth and 3000GT, remove rear seat cushion and remove access plate if required to disconnect fuel pump harness connector.
- On all models, start engine. Let engine run until it stops. Turn ignition off. Disconnect negative battery terminal. Connect fuel pump harness connector. Reinstall rear seat (if necessary.) WARNING: Before disconnecting high pressure fuel hose at fuel delivery pipe, cover fuel hose connection with a rag. Some residual fuel pressure may still be in system.
Scheme 1
- Disconnect high pressure fuel hose at fuel delivery pipe. Remove throttle body bracket (if necessary). Connect fuel pressure gauge with adapter between fuel delivery pipe and high pressure hose. (Scheme 1)
- Connect negative battery terminal. Operate fuel pump by connecting battery voltage to fuel pump test terminal. See «FUEL PUMP TEST TERMINAL LOCATION»(ref-18905-S33497693112001010800000) table. Ensure no fuel leaks are present. Disconnect battery voltage to fuel pump test terminal.
- Start engine and let idle. Measure fuel pressure with vacuum hose connected to fuel pressure regulator. Record fuel pressure reading. See «FUEL PUMP PERFORMANCE»(ref-18905-S15176435962001010800000) table. Disconnect and plug vacuum hose from fuel pressure regulator. Record fuel pressure reading.
- Check for fuel pressure in fuel return hose by gently pinching hose while increasing engine speed. If fuel volume is low, fuel pressure in return hose will not be felt. Increase engine speed to 2500-3000 RPM, 2-3 times. Return engine to idle. Fuel pressure should not drop when engine is returned to idle.
- Turn ignition off. On all models, ensure fuel pressure reading does not decrease within 2 minutes. On all models, if a decrease is noted, monitor speed of decrease.
- If fuel pressure is lower than specification, fuel pressure drops at idle after increasing engine speed to 2500-3000 RPM, or no fuel pressure in fuel return hose can be felt, check for clogged fuel filter, or faulty fuel pressure regulator or fuel pump.
- If fuel pressure is higher than specification, check for a faulty fuel pressure regulator or plugged fuel return line. If fuel pressure does not change when vacuum hose to regulator is connected or disconnected, check for a leaking or clogged vacuum hose to fuel pressure regulator or faulty fuel pressure regulator.
- If fuel pressure decreases suddenly after engine is stopped, check valve in fuel pump is not seated. Replace fuel pump. If fuel pressure drops slowly, fuel injector is leaking or fuel pressure regulator valve seat is leaking. Check for faulty fuel injector or fuel pressure regulator. Repair as necessary.
- When fuel pressure test is complete, repeat fuel pressure release procedure before disconnecting fuel pressure gauge. Install new "O" ring at end of high pressure hose. Check for fuel leaks. FUEL PUMP TEST TERMINAL LOCATION Application Wire Color Location Diamante Black/Blue (1) Stealth & 3000GT Black/Blue (2) (1) On main wiring harness, near center of firewall. (2) On main wiring harness, near wiper motor on firewall, behind battery. FUEL PUMP PERFORMANCE Application At Idle W/Vacuum (1) At Idle W/O Vacuum (2) Diamante 38 (2.6) 47-50 (3.3-3.5) Stealth (Turbo) & 3000GT 34 (2.4) 43-45 (3.0-3.1) (1) With vacuum at pressure regulator. (2) Without vacuum at pressure regulator.
MPI Control Relay
Multipurpose relay switches power to vehicle sensors and actuators including airflow sensor, crank angle sensor, idle speed control, injectors and fuel pump. When ignition switch is turned to ON position, ECM energizes coils controlling injectors, airflow sensor and idle speed control. When ignition switch is turned to START position, ECM energizes coils (through inhibitor switch on A/T models) to supply power to fuel pump. Relay failure will cause a no-start condition. For testing procedure, refer to SYSTEM/COMPONENT TESTS article in this section.
SPARK
Check for spark at coil wire (if applicable) and at each spark plug wire using a high output spark tester. Check spark plug wire resistance on suspect wires. For wire resistance specification, see SPECIFICATIONS article in this section.
CRANKSHAFT POSITION SENSOR
For crank position sensor testing procedure, see SYSTEM/COMPONENT TESTS article in this section.
Scheme 2
- Using a DVOM, measure primary coil resistance between terminal No. 3 (power terminal) and each individual coil terminal. (Scheme 2) To check secondary coil resistance, measure resistance between towers of each individual coil.
- Replace coil if primary and secondary coil resistances are not within specification. See «IGNITION COIL RESISTANCE»(ref-18905-S37302422012001010800000) table. IGNITION COIL RESISTANCE (DOHC) - Ohms @ 68°F (20°C) Application Primary Secondary 3.0L.67-.81 11,300-15,300
Scheme 3
- To test section of power transistor that controls cylinders No. 1 and 4 of ignition coil, disconnect power transistor connector. Using a 1.5-volt dry cell battery, connect negative end of 1.5-volt battery to terminal No. 4 of power transistor and positive end to terminal No. 3. (Scheme 3)
- Using an analog ohmmeter, check for continuity between terminals No. 4 and 13 of power transistor. Continuity should exist. With positive end of 1.5-volt battery disconnected, there should be no continuity. Replace power transistor if it fails test.
- To test section of power transistor that controls cylinders No. 2 and 5 of ignition coil, connect negative end of 1.5-volt battery to terminal No. 4 of power transistor and positive end to terminal No. 2. (Scheme 3)
- Using an analog ohmmeter, check for continuity between terminals No. 4 and 12 of power transistor. Continuity should exist. With positive end of 1.5-volt battery disconnected, there should be no continuity. Replace power transistor if it fails test.
- To test section of power transistor that controls cylinders No. 3 and 6 of ignition coil, connect negative end of 1.5-volt battery to terminal No. 4 of power transistor and positive end to terminal No. 1. (Scheme 3)
- Using an analog ohmmeter, check for continuity between terminals No. 4 and 11 of power transistor. Continuity should exist. With positive end of 1.5-volt battery disconnected, there should be no continuity. Replace power transistor if it fails test.
Ignition Coil Resistance
Using a DVOM, measure primary coil resistance between positive and negative terminals of coil. (Scheme 4) Measure secondary coil resistance between coil positive terminal and ignition coil tower. Primary and secondary coil resistance should be within specification. See IGNITION COIL RESISTANCE table.
| Application | Primary | Secondary | |
|---|---|---|---|
| 3.0L (VIN H) | |||
| Diamante & Stealth | .72-.88 | 10,300-13,900 | |
IGNITION COIL RESISTANCE (SOHC) - Ohms @ 68°F (20°C)
Ignition Coil Connector ID (SOHC). Scheme 4
Scheme 5
- Disconnect power transistor connector. Using a 1.5-volt dry cell battery, connect negative end of 1.5-volt battery to terminal No. 2 of power transistor and positive end to terminal No. 1. (Scheme 5)
- Using an analog ohmmeter, check for continuity between terminals No. 2 and 3 of power transistor. Continuity should exist. With positive end of 1.5-volt battery disconnected, there should be no continuity. Replace power transistor if it fails test. (Scheme 5): Power Transistor Connector ID (SOHC)
IDLE SPEED & IGNITION TIMING
Ensure idle speed and ignition timing are set to specification. See IGNITION TIMING table. For adjustment procedures, see ADJUSTMENTS article in this section.
| Application | (1) Basic | (2) (3) Actual | |
|---|---|---|---|
| 3.0L | |||
| Diamante | 3-7 @ 600-800 | 15 @ 600-800 | |
| Stealth & 3000GT | 2-8 @ 600-800 | 15 @ 600-800 | |
| (1) With ignition timing adjustment connector grounded or vacuum hose (farthest from distributor) disconnected. (2) With ignition timing adjustment connector ungrounded or vacuum hose (farthest from distributor) connected. Ignition timing may fluctuate. (3) If vehicle altitude is more than 2300 ft. above sea level, actual timing may be advanced. | |||
| (1) | With ignition timing adjustment connector grounded or vacuum hose (farthest from distributor) disconnected. |
| (2) | With ignition timing adjustment connector ungrounded or vacuum hose (farthest from distributor) connected. Ignition timing may fluctuate. |
| (3) | If vehicle altitude is more than 2300 ft. above sea level, actual timing may be advanced. |
IGNITION TIMING (Degrees BTDC @ RPM)
SUMMARY
If no faults were found while performing BASIC TESTING , proceed to G - TESTS W/ CODES article in this section. If no hard codes are found in TESTS W/CODES , proceed to TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.