Engine Controls - Basic Testing BMW M3 E36

INTRODUCTION

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 customer's complaint 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

1. 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»(/bmw/m3/e36-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing) table. Ensure battery is fully charged.
2. 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.
3. Using 16-mm Socket (12-1-171) and Torque Limiter (12-1-172), remove spark plugs. Use Pressure Gauge (11-0-162), Test Adapter (11-0-166) and Tube Extension (11-0-167) to check compression pressure. See ENGINE COMPRESSION SPECIFICATIONS table.

ENGINE COMPRESSION SPECIFICATIONS

DME & FUEL PUMP RELAY LOCATION

Exhaust System Backpressure

The exhaust system can be checked with a vacuum or pressure gauge. Remove oxygen sensor or air injection check valve (if equipped). Connect a 1-10 psi pressure gauge and run engine at 2500 RPM. If exhaust system backpressure is greater than 1 3/4-2 psi (.12-.14 kg/cm 2 ), exhaust system or catalytic converter is plugged.

If a vacuum gauge is used, connect vacuum gauge hose to intake manifold vacuum port and start engine. Observe vacuum gauge. Open throttle part way and hold steady. If vacuum slowly drops after stabilizing, check exhaust system for restrictions.

FUEL SYSTEM

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).

On 3-series, fuel pump relay is located in fuse/relay block on left rear corner of engine compartment. (Scheme 1)and (Scheme 2).

On 525i and 525iT, fuel pump relay is located on right rear corner of engine compartment, next to DME control unit and DME master relay. First relay (viewed from top to bottom) is Digital Motor Electronics (DME) master relay, followed by fuel pump relay and then oxygen sensor heater relay.

FUEL PRESSURE

Begin basic fuel system diagnosis by determining fuel system pressure.

1. Remove engine cover to gain access to fuel lines. Connect Pressure Gauge (13-3-060) and "T" Fitting (13-3-064) in fuel lines in front of fuel pressure regulator. Block (plug) fuel return line with Fuel Hose Clamp (13-3-010).
2. Remove fuel pump relay. See «DME & FUEL PUMP RELAY LOCATION»(/bmw/m3/e36-1992-1999/remont/testing-diagnostics/#engine-controls-basic-testing) table. Using Fuel Pump Relay Bridging Caliper (61-3-050) or jumper wire, connect (bridge) terminals No. 87 and 30 at fuel pump relay socket. (Scheme 1) This will turn fuel pump on.
3. Check fuel pump delivery pressure. To check fuel pump delivery rate, disconnect fuel return line. Install extension hose and hold end of hose in Graduated Glass Container (13-3-020). Check fuel pump delivery rate. See FUEL PUMP PERFORMANCE table.

FUEL PUMP PERFORMANCE

Scheme 1

Fuel Pump Relay

Remove fuel pump relay. Apply battery voltage to relay terminal No. 30 and terminal No. 86. (Scheme 2) 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 master (main) relay, DME/Motronic control unit and ground circuits going to fuel pump relay. See WIRING DIAGRAMS section. Only sockets No. 2, 4, 6 and 8 are used by relay.

Scheme 2

Direct Ignition System (DIS)

1. 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.
2. 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.
3. 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 master 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 3) Secondary coil resistance cannot be measured. See IGNITION COIL RESISTANCE table.

DIS Ignition Coil Schematic & Terminal Identification (3-Series). Scheme 3

Ignition Coil Primary Signal Check

1. Select 4-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 4) Connect Black lead to terminal No. 1 on Adapter (12-7-020).
2. 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 Coil Secondary Signal Check

1. Connect engine analyzer and Adapter (12-7-020) 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 5)
2. 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).

IGNITION COIL RESISTANCE - Ohms 68°F (20°C)

Checking DIS Ignition Coil Primary Signal. Scheme 4

Checking DIS Ignition Coil Secondary Signal. Scheme 5

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 TESTS W/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.

Wiring Diagram (325i, 325iC & 325is 2.5L - 1 Of 2). Scheme 6

Wiring Diagram (325i, 325iC & 325is 2.5L - 2 Of 2). Scheme 7

Wiring Diagram (525i & 525iT 2.5L - 1 Of 2). Scheme 8

Wiring Diagram (525i & 525iT 2.5L - 2 Of 2). Scheme 9

See also:
• DME & FUEL PUMP RELAY LOCATION