INTRODUCTION
Note. Vehicles are equipped with an OBD-II diagnostic system, with an OBD-II Data Link Connector (DLC). See TESTS W/O CODES article.
The following diagnostic steps will help prevent overlooking a simple problem. This is also where to begin diagnosis for a no-start condition.
The first step in diagnosing any driveability problem is verifying the problem with a test drive under the conditions the problem reportedly occurred.
Before entering self-diagnostics, perform a careful and complete visual inspection. Most engine control problems result from mechanical breakdowns, poor electrical connections or damaged/misrouted vacuum hoses. Before condemning the computerized system, perform each test listed in this article.
Note. Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure.
VISUAL INSPECTION
Visually inspect all electrical wiring, looking for chafed, stretched, cut or pinched wiring. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and are not pinched or cut. Inspect air induction system for possible vacuum leaks.
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 table. Ensure battery is fully charged.
- 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 ENGINE COMPRESSION SPECIFICATIONS table.
| Application | Specification | ||
|---|---|---|---|
| Compression Ratio | |||
| 4-Cylinder | 10.0:1 | ||
| 6-Cylinder | |||
| M3, Z3 & 328 Series | 10.2:1 | ||
| 323 Series | 10.5:1 | ||
| V8 | 10.0:1 | ||
| Compression Pressure | |||
| All Models | 142-156 psi (10-11 kg/cm 2 ) | ||
COMPRESSION SPECIFICATIONS
| Application | Location | |
|---|---|---|
| Z3 | ||
| DME Relay | Under Left Side Of Instrument Panel, Next To Kick Panel | |
| Fuel Pump Relay | Right Rear Corner Of Engine Compartment, Next To DME ECU | |
| 3-Series (1) | ||
| DME & Fuel Pump Relays | Left Rear Corner Of Engine Compartment, In Relay Box | |
| 5-Series & 7-Series | ||
| DME Relay | Right Rear Corner Of Engine Compartment, Next To DME ECU | |
| Fuel Pump Relay | Right Side Of Trunk | |
| 8-Series | ||
| DME & Fuel Pump Relays | Right Rear Corner Of Engine Compartment, Next To DME ECU | |
| (1) (Scheme 71)and (Scheme 72). | ||
| (1) | (Scheme 71)and (Scheme 72). |
DME & FUEL PUMP RELAY LOCATION
Scheme 71
Scheme 72
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. |
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 PRESSURE
Begin basic fuel system diagnosis by determining fuel system pressure.
- Remove engine cover to gain access to fuel lines. Connect Pressure Gauge (133060) and "T" Fitting (133064) in fuel lines in front of fuel pressure regulator. Block (plug) fuel return line with Fuel Hose Clamp (133010).
- Remove fuel pump relay. See DME & FUEL PUMP RELAY LOCATION table. Using Fuel Pump Relay Bridging Caliper (613050) or jumper wire, connect terminals No. 87 and 30 at fuel pump relay socket. (Scheme 73) 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 table.
| Application | Pressure psi (kg/cm 2 ) | Min. Vol. In 30 Sec. Pts. (L) |
|---|---|---|
| All Models | 43 | 1.85 (0.9) |
FUEL PUMP PERFORMANCE
Fuel Pump Relay
Remove fuel pump relay. Apply battery voltage to relay terminal No. 30 and terminal No. 86. (Scheme 73) Ground relay terminal No. 85. Voltage should now exist at relay terminal No. 87. Replace relay if it does not work as indicated.
Note. If relay does not work on vehicle, check battery feed, DME relay, ECU and ground circuits at fuel pump relay. See WIRING DIAGRAMS article.
Scheme 73
Direct Ignition System (DIS)
- 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.
Note. For location of DME and fuel pump relays, see DME & FUEL PUMP RELAY LOCATION table under PRELIMINARY INSPECTION & ADJUSTMENTS.
Ignition Coil Resistance
Measure primary coil resistance between terminal No. 1 and terminal No. 15. (Scheme 74) Secondary coil resistance cannot be measured. See IGNITION COIL RESISTANCE table.
Scheme 74
Ignition Coil Primary Signal Check
- Select cylinder mode on BMW SERVICE TESTER (Sun 2013 Engine Analyzer). Connect universal adapter lead on tester. Connect Brown lead to known good engine ground. (Scheme 75) Connect Black lead to terminal No. 1 on Adapter (127020).
- Connect adapter to ignition coil of cylinder being tested. Red lead is not used as only one cylinder can be measured. Engine speed displayed will be reduced by a factor of 4. Produce stopped signal on oscilloscope by pressing "R" button on tester. Combustion voltage line will be very erratic on oscilloscope pattern (this is normal).
Ignition Voltage Too High
Check for excessive spark plug electrode gap, high compression, lean air/fuel mixture, low electrode temperature, or burnt spark plug electrode.
Ignition Voltage Too Low
Check for insufficient spark plug electrode gap, low compression, or high electrode temperature.
Ignition Coil Secondary Signal Check
- Connect engine analyzer and Adapter (127020) as described in IGNITION COIL PRIMARY SIGNAL CHECK. Remove ignition coil. Connect a spark plug wire (between coil and spark plug) to cylinder being tested. Connect inductive pick-up Blue lead, on lead to cylinder being tested. (Scheme 76)
- Produce stopped signal on oscilloscope by pressing "R" button on tester. Display of ignition signal on oscilloscope will be strongest when inductive clip and Black lead are connected to same cylinder. Display on oscilloscope may be disturbed by neighboring ignition leads (this is normal).
| Primary | Secondary |
|---|---|
| .8 (1) | Not Measurable |
| (1) Specification is approximate | |
| (1) | Specification is approximate |
IGNITION COIL RESISTANCE - Ohms @ 68°F (20°C)
Checking DIS Ignition Coil Primary Signal. Scheme 75
Checking DIS Ignition Coil Secondary Signal. Scheme 76
IDLE SPEED & IGNITION TIMING
Ensure idle speed and ignition timing are set to specification. For adjustment procedures, see ADJUSTMENTS article.
SUMMARY
If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to G - TESTS W/O CODES article. If no hard codes are found in self-diagnostics, or vehicle does not have a self-diagnostic system, proceed to TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.), or intermittent diagnostic procedures.
See also:
• TESTS W/O CODES
• G - TESTS W/O CODES