Engine Controls - Basic Testing Mercury Capri III

INTRODUCTION

The following diagnostic steps help prevent overlooking simple problems and begin diagnosis for a no-start condition.

The first step in diagnosing any driveability problem is to verify the complaint. Test drive the vehicle under the conditions in which 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. Unless stated otherwise in test procedure, perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance.

VISUAL INSPECTION

Perform a visual inspection of all electrical wiring. Look for chafed, stretched, cut or pinched wiring. Ensure electrical connections fit tightly and are not corroded. Ensure vacuum hoses are properly routed and are not cut or pinched. If necessary, see VACUUM DIAGRAMS article in the ENGINE PERFORMANCE Section to verify routing and connections. Inspect air induction system for possible vacuum leaks.

Compression

Engine mechanical condition can be checked using a compression gauge, vacuum gauge or engine analyzer. See engine analyzer instruction manual for specific instructions. Lowest compression reading must be not less than 75 percent of highest reading.

Exhaust System Backpressure

Exhaust system can be checked with a vacuum gauge or a 0-5 psi pressure gauge. If a pressure gauge is used, remove O2 sensor. Connect gauge to O2 sensor port. Start engine, and run at 2500 RPM. If exhaust system backpressure is more than 2 psi, exhaust system or catalytic converter is plugged.

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

FUEL PRESSURE

Note. For 1991 fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. For 1992 fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article.

Fuel Pressure Release

Start engine (if possible), and unplug VAF meter connector. When engine stalls, turn ignition off and reconnect VAF meter wiring. Using shop towel, cover fitting to absorb leakage when opening fuel system.

Fuel Pressure Check

1. Connect fuel pressure gauge between fuel filter and fuel rail. Open main valve, and close drain valve. Locate fuel pump check connector in engine compartment, near left strut. Connect jumper wire between fuel pump test terminals (Black and Green/White wires on Capri or Black and Green/Red wires on Festiva).
2. Turn ignition on to activate fuel pump. If pump does not run, check fuel pump circuit. If possible, start engine. Measure and record fuel pressure. For fuel pressure specifications, see «FUEL PRESSURE SPECIFICATIONS»(ref-123316) article. Disconnect vacuum from pressure regulator. Turn engine off. Wait 5 minutes and ensure residual pressure is at least 21 psi (1.5 kg/cm 2 ).
3. Operate fuel pump by reconnecting jumper wire at fuel pump check connector. Check fuel pump performance. Pinch hose between pressure gauge and fuel filter. Do not hold longer than necessary to check pressure.For fuel pressure specifications, see «FUEL PRESSURE SPECIFICATIONS»(ref-123316) article. If pump does not meet specifications, check fuel pump circuit, fuel pump, fuel tank and fuel filter or replace fuel pump.

FUEL PUMP PERFORMANCE

Fuel Pump Circuit

1. Turn ignition on. Connect jumper wire between fuel pump test connector terminals. (Scheme 1)or (Scheme 2). Turn ignition on to activate fuel pump.
2. Listen for fuel pump sound. If there is no sound, check main fuse, inertia switch (located at left rear shock tower), fuel pump relay, fuel pump and all electrical connections.

Scheme 1

Scheme 2

Fuel Pump Relay

Remove fuel pump relay (located near heater duct under carpet). Apply positive 12 volts to relay terminals "A" and "B" together. (Scheme 3) Measure voltage between terminal "C" and ground, while individually grounding terminals "D" and "E". Ensure voltage is as specified. See FUEL PUMP RELAY SPECIFICATIONS table. If voltage is not as specified, replace relay.

FUEL PUMP RELAY SPECIFICATIONS

Scheme 3

Firing Order

Inspect spark plug wiring routing. Ensure firing order is 1-3-4-2.

Spark

1. Crank engine. Check for a strong Blue spark at each spark plug wire by using a high output spark tester. Ensure resistance of each spark plug wire is 4000-6000 ohms per foot.
2. Disconnect and inspect all related ignition system connectors and harness. Clean or repair as necessary, and recheck spark. If still no spark, go to «IGNITION COIL POWER SOURCE»(/mercury/capri/iii-1990-1995/remont/testing-diagnostics/#engine-controls-basic-testing__ignition-coil-power-source) .

Ignition Coil Power Source

Disconnect primary wires at ignition coil. Turn ignition on. Measure voltage between Black/White wire on harness connector and ground. If voltage is not greater than 10 volts, check battery feed, ignition switch and fusible links. If voltage is greater than 10 volts, go to IGNITION COIL RESISTANCE .

Ignition Coil Resistance

Measure resistance between primary terminals of coil. Measure resistance between positive primary terminal and coil tower. See IGNITION COIL RESISTANCE table. Verify resistance between coil case and primary positive terminal is infinite. Replace coil if resistance measurements are not within specifications.

IGNITION COIL RESISTANCE

IDLE SPEED & IGNITION TIMING

Ensure idle speed and ignition timing are set to specification. For adjustment procedures, see ON-VEHICLE ADJUSTMENTS article.

SUMMARY

If no faults were found while performing BASIC TESTING , proceed to TESTS W/CODES article in the ENGINE PERFORMANCE Section. If no hard codes are found in self-diagnostics, proceed to 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.

See also:
• FUEL PRESSURE SPECIFICATIONS
• FUEL PUMP RELAY SPECIFICATIONS
• IGNITION COIL POWER SOURCE
• IGNITION COIL RESISTANCE