Engine Controls - Basic Testing - Gasoline Dodge Caravan II

INTRODUCTION

Following diagnostic steps can help prevent overlooking a simple problem. Also use this article to begin diagnosis for a no-start condition. First step in diagnosing any driveability problem is verifying customer's complaint with a test drive under conditions during which problem reportedly occurs.

Before entering self-diagnostics, perform a careful and complete visual inspection. Most driveability or no-start problems are not related to computerized engine control systems, but are in fact simple mechanical, electrical, fuel or vacuum related faults. Most engine control problems are results of mechanical breakdowns, poor electrical connections or damaged or misrouted vacuum hoses. Before condemning computerized engine control system, perform each test listed in this article.

Note. All voltage tests should be performed with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in testing procedures.

VISUAL INSPECTION

Perform a visual inspection of all electrical wirings. Look for chafed, stretched, cut or pinched wiring. Inspect electrical connectors and connections for tight fit and corrosion. Repair as necessary. Inspect all vacuum hoses for proper routing, cuts or pinches. If necessary, see appropriate VACUUM DIAGRAMS article in the ENGINE PERFORMANCE Section to verify routing and connections. Repair as necessary. Inspect air induction system for possible vacuum leaks.

Compression

Check engine mechanical condition using a compression gauge, vacuum gauge, or an engine analyzer capable of performing a relative compression test. See engine analyzer instruction manual for availability and description of relative compression feature.

ENGINE COMPRESSION

Exhaust System Backpressure

Check exhaust system using a vacuum gauge or pressure gauge. Remove O2 sensor or air injection check valve (if equipped). Connect a 1-5 psi (.07-.35 kg/cm 2 ) 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 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 steady. If vacuum gauge reading slowly drops after stabilizing, check exhaust system for restriction.

FUEL PRESSURE

Fuel Pressure Release (2.5L, 3.0L, 3.3L & 5.9L)

1. Fuel pressure must be fully released before opening fuel system or removing any fuel-carrying components. To release pressure in tank, open fuel tank cap slowly.
2. To release remaining pressure in system, disconnect injector wiring harness. Using jumper wire, connect injector harness ground terminal No. 1 to ground. (Scheme 1), (Scheme 2) or (Scheme 3). Connect injector harness positive terminal No. 2 to positive battery terminal with second jumper wire.
3. DO NOT keep injector connector connected to positive battery terminal for longer than 5 seconds. Remove jumper wires. This releases system pressure. Continue fuel system service.

Scheme 1

Scheme 2

Scheme 3

Fuel Pressure Release (3.9L & 5.2L)

1. Disconnect negative battery cable. Slowly open fuel cap to release fuel tank pressure. Remove protective cap from pressure test port on fuel rail. CAUTION: To minimize fuel spill, wrap a shop towel around and under pressure test port.
2. Using Fuel Pressure Gauge/Hose Tool (5069) with gauge removed, place gauge end of hose into approved gasoline container. To release pressure, screw other end of hose onto pressure test port. After pressure is released, remove hose from test port and continue fuel system service. When servicing is completed, install protective cap on fuel rail test port.

Fuel Pump Test

1. Begin basic diagnosis of fuel system by determining fuel system pressure. On 2.5L, 3.0L and 5.9L engines, release fuel pressure. See FUEL PRESSURE RELEASE. Disconnect fuel supply hose. Connect fuel system pressure Gauge (C-4799-B) between fuel supply hose and engine fuel line. NOTE: On 3.3L, 3.9L and 5.2L, vacuum supply line at fuel pressure regulator must be disconnected to obtain accurate pressure readings.
2. On 3.3L, 3.9L and 5.2L, disconnect vacuum supply line from fuel pressure regulator. Release fuel pressure. See FUEL PRESSURE RELEASE. Connect fuel pressure gauge at fuel rail test port.
3. On all models, turn ignition switch to ON position. Using Diagnostic Readout Box (DRB-II), activate fuel pump. If fuel pump pressure is at specification, fuel system is functioning properly. See FUEL PUMP PRESSURE SPECIFICATIONS table.
4. If fuel pressure is less than specification, record pressure. Repeat FUEL PRESSURE RELEASE procedure. Install fuel pressure gauge in fuel supply line at rear of vehicle between fuel tank and fuel filter.
5. Using DRB-II, activate fuel pump. Record pressure reading. If fuel pressure is 5 psi (.35 kg/cm 2 ) more than first pressure reading, replace fuel filter.
6. If no change in pressure reading is observed, gently squeeze fuel return hose. If fuel pressure increases, replace fuel pressure regulator. If no change in fuel pressure is observed, problem is plugged fuel pump filter sock or defective fuel pump.
7. If fuel pressure is more than specification, repeat fuel pressure release procedure. See FUEL PRESSURE RELEASE. Ensure fuel tank is at least half full. Remove fuel return hose at chassis line at fuel tank. Connect an extension hose to return hose. Place hose in an approved container with at least a 2 gallon capacity.
8. Using DRB-II, activate fuel pump. If fuel pressure is now within specification, check in-tank return fuel hose for kinking. Replace fuel pump assembly if in-tank reservoir check valve or aspirator jet is plugged.
9. On 2.5L and 5.9L, remove fuel return hose from throttle body if fuel pressure is still more than specification. Connect a substitute hose to throttle body return nipple. Place other end of hose in an approved container. On 3.0L and 3.3L, remove fuel return hose from fuel tubes at engine. Connect Fuel Test Connect Adapter (6541) to fuel return hose, and place other end in an approved container.
10. Using DRB-II, activate fuel pump. If fuel pressure is at specification, check for a restricted fuel return line between throttle body, or fuel tubes at engine, and fuel tank. If no change is observed, replace fuel pressure regulator.

FUEL PUMP PRESSURE SPECIFICATIONS

AUTO SHUTDOWN (ASD) RELAY

Note. If ASD relay is suspected of causing a fuel or ignition system malfunction, use Diagnostic Readout Box (DRB-II) to diagnose ASD relay. See appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section.

2.5L, 3.0L, 3.9L, 5.2L & 5.9L

When distributor signal is not present with ignition switch in RUN position, ASD relay turns off power to electric fuel pump, fuel injectors, ignition coil and O2 sensor heating element.

3.3L

When camshaft or crankshaft sensor signal does not exist with ignition switch in RUN position, ASD relay turns off power to electric fuel pump, fuel injectors, ignition coil and O2 sensor heating element.

TESTING SPARK AT COIL

Note. Ignition components may be damaged if test is performed with more than 1/4" clearance between wire and engine ground.

1. Remove coil wire from distributor cap. Hold end of cable 1/4" from engine ground. Crank engine and check for spark from coil wire. Spark should be present and constant.
2. If spark is present and constant, continue cranking engine. Slowly move coil wire away from ground. As coil wire is moved away from ground, check for arching at coil tower. If arching at coil tower is present, replace coil.
3. If spark is good and no arching is present, secondary ignition system is producing necessary voltage. Ensure spark reaches spark plugs by checking condition of rotor, cap, spark plug wires and spark plugs. Repair or replace as necessary. If ignition system components are in good condition, ignition system is okay. If vehicle still fails to start, proceed to NO-START TEST.

1. This system has 3 independent coils. These coils must be tested separately. Remove spark plug wire from No. 2 spark plug. Insert a clean screwdriver into spark plug boot.
2. Hold screwdriver approximately 1/4" from a ground. Crank engine, and watch for spark between screwdriver and ground. Repeat this test for No. 4 and No. 6 spark plug wires.
3. If no spark is present on any cylinder tested, go to NO-START TEST. If one or more cylinders has weak or no spark, go to next step.
4. Remove spark plug wires individually. Using an ohmmeter, measure resistance of each spark plug wire. Resistance should be 250-1,000 ohms per inch. Replace spark plug wire(s) if resistance is not within specification.
5. Disconnect electrical connector from coil pack. Measure resistance on primary side of each coil. Resistance should be.5-.7 ohm. Measure resistance between B+ terminal of ignition coil connector and corresponding cylinders. (Scheme 4) Replace coil if resistance is not within specification. NOTE: Each coil tower is labeled with corresponding cylinder number.
6. Remove spark plug wires from coil one at a time. Measure secondary resistance of ignition coil between grouped cylinders and coil towers. Resistance should be 7000-15,800 ohms. Replace coil if resistance is not within specification. If ignition system components are in good condition, ignition system is okay. If vehicle still fails to start, proceed to NO-START TEST.

Scheme 4

NO-START TEST

Note. Perform TESTING SPARK AT COIL before proceeding with NO-START TEST.

1. Unplug coil connector and coil. Connect a pair of jumper wires between coil and coil connector. Ensure sufficient battery voltage (12.4 volts) is available to crank engine and operate ignition systems. Crank engine for 5 seconds while monitoring voltage at coil positive terminal.
2. If voltage remains near zero during entire period of cranking, see appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section to check SBEC and ASD relay. If voltage is near battery voltage and drops to zero after 1-2 seconds of cranking, see appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section to check distributor pick-up circuit to SBEC.
3. If voltage remains near battery voltage during entire 5 seconds, turn ignition switch to OFF position. Disconnect SBEC 60-pin connector. Check 60-pin connector for loose terminals (push-outs).
4. Remove positive lead from coil. Connect a jumper wire between positive battery terminal and coil positive terminal. Using a specially constructed jumper wire, momentarily ground SBEC harness connector terminal No. 19. (Scheme 5)and (Scheme 6). Spark should be generated when ground connection is disconnected.
5. If spark is generated, replace SBEC. If no spark is generated, use special jumper wire directly on coil negative terminal. If spark is produced, repair wiring harness for an open circuit. If no spark is produced, replace ignition coil.

Scheme 5

Scheme 6

1. Ensure sufficient battery voltage (12.4 volts) is available to operate cranking and ignition systems. Disconnect wiring connector from coil pack. Connect a test light between B+ coil pack wiring connector terminal (Dark Green wire with Black tracer) and ground. (Scheme 7)
2. Turn ignition switch to ON position. DO NOT return ignition switch to OFF position. If test light flashes momentarily, SBEC energizes ASD relay, go to step 3). If test light does not flash, ASD relay did not energize, see appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section to check SBEC and ASD relay.
3. Crank engine for 5 seconds. If test light momentarily flashes during cranking, engine controller is not receiving signal. See appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section to check camshaft sensor and sensor circuits. If test light does not flash, unplug camshaft sensor connector.
4. Turn ignition switch to OFF position, then to ON position. Wait for test light to momentarily flash once then crank engine. If test light flashes once again, replace shorted camshaft sensor. If test light does not flash, see appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section to check crankshaft sensor/camshaft sensor 9-volt supply or crankshaft sensor 5-volt output to ground circuits.

Scheme 7

IDLE SPEED & IGNITION TIMING

Ensure idle speed and ignition timing are set to specification. Always refer to emission control information label in engine compartment before servicing. If manual and emission label specifications differ, always use specifications on emission label. For adjustment procedures, see appropriate ADJUSTMENTS article in the ENGINE PERFORMANCE Section.

SUMMARY

If no faults were found while performing BASIC TESTING , proceed to appropriate TESTS W/CODES article in the ENGINE PERFORMANCE Section. If no hard codes are found in self-diagnostics, proceed to appropriate TESTS W/O CODES article in the ENGINE PERFORMANCE Section for diagnosis by symptom (i.e., ROUGH IDLE, NO-START, etc.) or intermittent diagnostic procedures.