Compression
- Deactivate fuel injection system by removing Digital Motor Electronics (DME) master relay and fuel pump relay before performing compression test. See «DME & FUEL PUMP RELAY LOCATION»(ref-11857-S18725615982002022500000) table. Ensure battery is fully charged. DME & FUEL PUMP RELAY LOCATION (1) Application Location 3-Series Z3 DME Relay Right Rear Corner Of Engine Compartment, Next To DME ECU Fuel Pump Relay Under Left Side Of Instrument Panel, Next To Kick Panel E46 DME Relay Left Rear Corner Of Engine Compartment, In Relay/ECU Box Fuel Pump Relay Behind Glove Box 5-Series & 7-Series (2) DME Relay Right Rear Corner Of Engine Compartment, Next To DME ECU Fuel Pump Relay Right Side Of Trunk (1) For illustration of relay location, see «RELAYS»(ref-11860-S07649275462000120100000) under RELAYS & SOLENOIDS in SYSTEM & COMPONENT TESTING article. (2) V12 vehicles use 2 DME relays.
- Ensure engine coolant temperature does not exceed 95°F (35°C). Turn 2 fasteners on electric lead cover 90 degrees and remove electric lead cover. Repeat for other cover on V8 engines. Disconnect spark plug connectors.
- Using 16-mm Socket (121171) and Torque Limiter (121172), remove spark plugs. Use Pressure Gauge (110162), Test Adapter (110166) and Tube Extension (110167) to check compression pressure. See «COMPRESSION SPECIFICATIONS»(ref-11857-S14108048772002022500000) table. COMPRESSION SPECIFICATIONS Application Specification Compression Pressure 6-Cylinder 142-156 psi (10-11 kg/cm 2 ) V8 170-199 psi (12-14 kg/cm 2 ) V12 142-170 psi (10-12 kg/cm 2 )
Exhaust System Backpressure
The exhaust system can be tested with a vacuum or pressure gauge. If using a pressure gauge, remove HO2S 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 2 psi, exhaust system or catalytic converter is plugged.
If using a vacuum gauge, connect vacuum gauge hose to intake manifold vacuum port. Start engine. Observe vacuum gauge. Open throttle part way and hold steady. If vacuum gauge indication slowly drops after stabilizing, inspect exhaust system for 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. |
Oscilloscope Pattern
Evaluate ignition voltage peaks in response to sudden accelerator loads. Voltage peak No. 1 indicates dying-out process is not much higher than ignition voltage peak. Ignition system is okay. If beginning of dying-out process is considerably higher than ignition voltage peak as is shown in voltage peak No. 2, there is a fault in injection system such as lean mixture, defective injection valve or low compression. (Scheme 21)
Scheme 21
FUEL SYSTEM PRESSURE RELEASE
Fuel system pressure release procedure is not available from manufacturer. It may be possible to remove fuel pump relay, start engine and run engine until fuel pressure drops (engine stalls). See DME & FUEL PUMP RELAY LOCATION table.
FUEL VOLUME & PRESSURE
Begin basic fuel system diagnosis by determining fuel system pressure.
- Remove engine cover to gain access to fuel lines. Prepare Pressure Testing Kit (135220) which consists of Check Valve (135221) and Adapter (135222). Remove dust cap from measuring valve on fuel rail. Connect check valve and gauge to fuel rail. Block (plug) fuel return line with Fuel Hose Clamp (133010).
- Remove fuel pump relay. See «DME & FUEL PUMP RELAY LOCATION»(ref-11857-S18725615982002022500000) table. Using Fuel Pump Relay Bridging Caliper (613050) or jumper wire, connect terminals No. 87 and 30 at fuel pump relay socket. (Scheme 22) This will turn fuel pump on.
- Disconnect fuel return line. Install extension hose and hold end of hose in Graduated Glass Container (133020). Check fuel pump delivery rate. See «FUEL PUMP PERFORMANCE»(ref-11857-S00800828482000120100000) table. FUEL PUMP PERFORMANCE Application Pressure psi (kg/cm 2 ) Min. Vol. In 30 Sec. Pts. (L) 6-Cylinder & V8 50 (3.5) 1.85 (0.9) V12 50 (3.5) 2.3 (1.1)
Fuel Pump Relay
Note. If relay does not work on vehicle, check battery feed, DME relay, PCM and ground circuits at fuel pump relay. See WIRING DIAGRAMS article.
Remove fuel pump relay. Apply battery voltage to relay terminal No. 30 and terminal No. 86. (Scheme 22) Ground relay terminal No. 85. Voltage should now exist at relay terminal No. 87. Replace relay if it does not work as indicated.
Scheme 22
SERVICING PRECAUTIONS
Note. For location of DME and fuel pump relays, see DME & FUEL PUMP RELAY LOCATION table under PRELIMINARY INSPECTION & ADJUSTMENTS.
- Ensure ignition is turned off before working on the ignition system. The engine may not be started without a connected secondary circuit. When checking compression, remove Digital Motor Electronics (DME) master relay.
- DO NOT connect shielded capacitors to terminal No. 1 of the ignition coil. DO NOT connect terminal No. 1 of the ignition coil to ground or battery positive terminal, as this will damage ignition stages in DME control unit.
- DO NOT connect DVOM or test light to terminal No. 1 of ignition coil while engine is running. High tension (350 volts) is present at coil terminal No. 4, secondary ignition leads, spark plugs and ignition coil terminal No. 1 to DME control unit.
Ignition Voltage
See IGNITION VOLTAGE CHECK table.
| Component Or Condition | Result | |
|---|---|---|
| Ignition Voltage Too High | ||
| Electrode Gap | Large | |
| Compression | High | |
| Fuel Air Mixture | Lean | |
| Electrode Temperature | Low | |
| Electrode Condition | Burned | |
| Ignition Lead | Interrupted | |
| Ignition Voltage Too Low | ||
| Electrode Gap | Small | |
| Compression | Low | |
| Fuel Air Mixture | Correct | |
| Electrode Temperature | High | |
| Electrode Condition | New | |
IGNITION VOLTAGE CHECK
Direct Ignition System (DIS)
Measure primary coil resistance between terminal No. 1 and terminal No. 15. (Scheme 23) Secondary coil resistance cannot be measured. See IGNITION COIL RESISTANCE table.
Scheme 23
| Primary | Secondary |
|---|---|
| .8 (1) | Not Measurable |
| (1) Specification is approximate | |
| (1) | Specification is approximate |
IGNITION COIL RESISTANCE - Ohms @ 68°F (20°C)
Distributor Ignition System (V12)
Note. For location of DME and fuel pump relays, see DME & FUEL PUMP RELAY LOCATION table under PRELIMINARY INSPECTION & ADJUSTMENTS.
Switch off ignition. Remove distributor cap with ignition wiring harness. See REMOVAL, OVERHAUL & INSTALLATION article. Perform resistance measurement on individual components. See DISTRIBUTOR SPECIFICATIONS table. Check distributor rotor and distributor cap for hairline cracks and traces of scorching. If any are present, establish the cause and replace corresponding component.
| Application | Specification |
|---|---|
| Winding Resistance | (1) 1.1k Ohms |
| Clearance Between Stator & Rotor Tooth | .011-.027" (.3-.7 mm) |
| Angled Plugs/Shielded Plugs | (1) 1k Ohm |
| Spark Plug Connectors | (1) 5k Ohms |
| Ignition Lead @ 68°F (20°C) | (1) 20 Meg Ohms |
| Distributor | (1) 1k Ohm |
| Position Sensor Coil Resistance | (1) 80 Ohms |
| (1) Specification is approximate. | |
| (1) | Specification is approximate. |
DISTRIBUTOR SPECIFICATIONS
IDLE SPEED & IGNITION TIMING
Idle speed and ignition timing are not adjustable. For further information, see ON-VEHICLE ADJUSTMENTS article. See IDLE SPEED table.
| Application | Idle RPM (1) |
|---|---|
| 6-Cylinder & V8 | 650-750 |
| V12 | 530-630 |
| (1) With A/C off and transmission in neutral. | |
| (1) | With A/C off and transmission in neutral. |
IDLE SPEED
SUMMARY
If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to SELF-DIAGNOSTICS article. If no hard codes are found in self-diagnostics, or vehicle does not have a self-diagnostic system, proceed to TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.), or intermittent diagnostic procedures.