Compression
Note. Manufacturer does not provide a compression specification (psi). Manufacturer identifies if compression pressure difference between cylinders is 25 percent or less, compression pressure is acceptable.
Release fuel system pressure. See FUEL PRESSURE RELEASE under FUEL SYSTEM. Install a remote starter switch to starter circuit. Remove spark plugs and install a compression gauge. Crank engine a minimum of 5 strokes and record highest compression reading. See COMPRESSION SPECIFICATIONS table.
| Application | Specification | ||
|---|---|---|---|
| Compression Ratio | |||
| S-Type | |||
| 3.0L | 10.5:1 | ||
| 4.0L | 10.75:1 | ||
| XJR, XJ8 & XK8 | |||
| Normally Aspirated | 10.75:1 | ||
| Supercharged | 9.0:1 | ||
| Compression Pressure | (1) | ||
| Maximum Variation Between Cylinders | 25% | ||
| (1) Information is not available from manufacturer. | |||
| (1) | Information is not available from manufacturer. |
COMPRESSION SPECIFICATIONS
Exhaust System Backpressure
The exhaust system can be checked with a vacuum or pressure gauge. If using a pressure gauge, remove oxygen sensor. Connect a 0-5 psi pressure gauge and run engine at 2500 RPM. If exhaust system backpressure is greater than 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 RELEASE
Turn ignition off. Locate service valve in fuel line, in engine compartment. Connect a suitable hose to service valve. Release fuel pressure by opening service valve and draining fuel into a suitable container.
FUEL PRESSURE
| WARNING | Always relieve fuel pressure before disconnecting any fuel injection-related component. DO NOT allow fuel to contact engine or electrical components. |
S-Type
Information is not available from manufacturer.
XJR, XKR, XJ8 & XK8
Regulated fuel pressure should be 43.5 psi (300 kPa) more than intake manifold pressure.
INJECTOR RESISTANCE
Turn ignition off. Disconnect appropriate injector harness connector. Measure resistance between injector terminals. On S-Type, resistance should be 12-16 ohms. On XJR, XKR, XJ8 and XK8, resistance should be 12-18 ohms. On all models, replace injector if resistance is not as specified.
IGNITION COIL
Turn ignition off. Disconnect appropriate ignition coil harness connector. Measure resistance between ignition coil terminals. On S-Type, resistance should be.5-1.0 ohm. On XJR, XKR, XJ8 and XK8, resistance should be.54-1.04 ohms. On all models, replace ignition coil if resistance is not as specified.
IDLE SPEED & MIXTURE
Idle speed and mixture are electronically controlled by Engine Control Module (ECM) or Powertrain Control Module (PCM). No adjustment is necessary.
IGNITION TIMING
Ignition timing is electronically controlled by Engine Control Module (ECM) or Powertrain Control Module (PCM). No adjustment is necessary.
SUMMARY
If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to appropriate SELF-DIAGNOSTICS article. If no hard codes are found in self-diagnostics, go to TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.), or intermittent diagnostic procedures.