Compression
Check engine mechanical condition with a compression gauge, vacuum gauge, or an engine analyzer. See engine analyzer manual for specific instructions. Depressurize fuel system before checking engine compression. See FUEL SYSTEM below in this article.
| CAUTION | DO NOT use ignition switch during compression tests on fuel injected vehicles. Use a remote starter to crank engine. Fuel injectors are triggered by the ignition switch during cranking mode, which can cause a fire hazard, or contaminate the engine's oiling system. |
| Application | Specification |
|---|---|
| Compression Ratio | 9.5:1 |
| Compression Pressure | (1) 160-170 psi (11.2-12.0 kg/cm 2 ) |
| Maximum Variation Between Cylinders | 10 psi (.70 kg/cm 2 ) |
| (1) Minimum cranking speed is 300 RPM. | |
| (1) | Minimum cranking speed is 300 RPM. |
COMPRESSION SPECIFICATIONS
Exhaust System Backpressure
The exhaust system can be checked with a vacuum or pressure gauge. If using a 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 it steady. If vacuum gauge reading slowly drops after stabilizing, check exhaust system for restriction.
FUEL PRESSURE
| CAUTION | ALWAYS relieve fuel pressure before disconnecting any fuel injection-related component. DO NOT allow fuel to contact engine or electrical components. |
Fuel Pressure Release
- Disconnect fuel pump relay in right front corner of trunk. Relay is front-most relay (Silver relay with Yellow Connector).
- Start engine and let idle until engine stalls. Turn ignition off. Install fuel pump relay.
Scheme 1
SPARK PLUG WIRES
Using a high output spark tester, check for spark at coil wire and at each spark plug wire. Check spark plug wire resistance on suspected wires. See the SPECIFICATIONS article for specifications on spark plug wire resistance.
IGNITION COIL
See IGNITION COIL RESISTANCE table.
| Application | Primary | Secondary |
|---|---|---|
| XJS & XJ6 | 0.5 | 6000 |
IGNITION COIL RESISTANCE - OHMS @ 68°F (20°C)
IDLE SPEED
Ensure idle speed is set to specification. Refer to the IDLE SPEED SPECIFICATIONS table below in this article. For adjustment procedures, see the ADJUSTMENTS article in this section.
IGNITION TIMING
Ignition timing is electronically controlled by Electronic Control Module (ECM). Ignition timing adjustment is not necessary.
| Application | RPM |
|---|---|
| XJS & XJ6 | 650-750 |
IDLE SPEED SPECIFICATIONS
SUMMARY
If no faults were found while performing the BASIC DIAGNOSTIC PROCEDURES in this article, see the TESTS W/CODES article. If no hard codes are found in self-diagnostics, see TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.), or intermittent diagnostic procedures.