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 | Psi (kg/cm 2 ) |
|---|---|
| Normal Compression Pressure | 170-225 (11.9-15.8) |
| Minimum Compression Pressure | 100 (7.0) |
| Maximum Variation Between Cylinders | (1) |
| (1) Maximum variation between cylinders is 25 percent. | |
| (1) | Maximum variation between cylinders is 25 percent. |
COMPRESSION SPECIFICATIONS
FUEL PRESSURE RELEASE
| WARNING | Always release fuel pressure before disconnecting any fuel injection-related component. DO NOT allow fuel to contact engine or electrical components. |
| CAUTION | When battery is disconnected, vehicle computer and memory systems may lose memory data. Driveability problems may exist until computer systems have completed a relearn cycle. See COMPUTER RELEARN PROCEDURES article in the GENERAL INFORMATION section before disconnecting battery. |
- Disconnect negative battery cable. Remove fuel tank cap to release fuel tank pressure.
- Remove protective cap from fuel pressure test port on fuel rail. Fuel pressure test port is located at center of fuel rail. Place end of Fuel Pressure Gauge Hose (C-47991) into approved gasoline container.
- Screw remaining end of fuel pressure gauge hose onto fuel pressure test port. Fuel pressure will be released into gasoline container.
- After fuel pressure is released, remove fuel pressure gauge hose from fuel pressure test port. Reinstall protective cap on fuel pressure test port and fuel tank cap. Reinstall negative battery cable.
FUEL PUMP RELAY
The Powertrain Control Module (PCM) controls fuel pump relay operation by controlling fuel pump relay ground circuit. PCM opens ground circuit when ignition is off, and completes ground circuit when ignition is on, to provide fuel pump operation. When ignition is first turned on, if crankshaft position sensor does not detect engine rotation, PCM de-energizes fuel pump relay after approximately one second.
Fuel pump relay receives battery voltage from fuse or fusible link depending on application. If fuel pump relay or control circuit becomes defective, a Diagnostic Trouble Code (DTC) may be stored in the PCM. See the TESTS W/CODES - 2.4L article. For additional information on diagnosis for fuel pump relay and control circuit, see NO START (NS) TEST in the TESTS W/CODES - 2.4L article.
IGNITION CHECKS
Note. For ignition system spark testing and component testing, see appropriate NO TROUBLE CODE (NTC) TEST and NO START (NS) TEST in the TESTS W/CODES - 2.4L article.
IDLE SPEED & IGNITION TIMING
Ensure idle speed and ignition timing are set to specification. For adjustment procedures, see ADJUSTMENTS - 2.4L article.
SUMMARY
If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to the TESTS W/CODES - 2.4L article. If no diagnostic trouble codes are found in self-diagnostics, proceed to TESTS W/O CODES - 2.4L article for diagnosis by symptom (i.e., ROUGH IDLE, NO-START, etc.) or intermittent diagnostic procedures.