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Engine Controls - Basic Testing: Other Honda Prelude IV

Testing & Diagnostics 3 illustrations ~927 words

Compression

Check engine mechanical condition with a compression gauge, vacuum gauge, or an engine analyzer. See engine analyzer manual for specific instructions.

WARNINGDO NOT use ignition switch during compression tests on fuel injected vehicles. Use a remote starter to crank engine. Fuel injectors on many models are triggered by ignition switch during cranking mode, which can create a fire hazard or contaminate the engine's oiling system.

Check compression pressure with engine at normal operating temperature, all spark plugs removed, throttle valves wide open and at specified cranking speed. Crank engine at least 6 revolutions to determine engine compression. See ENGINE COMPRESSION table.

ModelStandard psi (kg/cm 2 )Minimum psi (kg/cm 2 )Minimum RPM
Prelude (1)178 (12.5)135 (9.5)250
(1) Maximum variation between cylinders is 28 psi (2.0 kg/cm 2 ).
(1)Maximum variation between cylinders is 28 psi (2.0 kg/cm 2 ).

ENGINE COMPRESSION

Exhaust System Backpressure

Exhaust system can be checked using a vacuum or pressure gauge. Remove oxygen sensor (O2S) or heated oxygen sensor (HO2S). Connect a 0-5 psi pressure gauge, and run engine at 2500 RPM. If exhaust system backpressure exceeds 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 slowly drops after stabilizing, check exhaust system for restrictions.

FUEL SYSTEM

WARNINGAlways relieve fuel pressure before disconnecting any fuel injection-related component. DO NOT allow fuel to contact engine or electrical components.

FUEL SYSTEM PRESSURE RELEASE

Remove negative battery cable. Loosen fuel tank filler cap. Locate 6-mm service bolt on fuel rail. Place clean shop rag around service bolt. To relieve system pressure, slowly loosen service bolt one complete turn. Always replace washer under 6-mm service bolt after loosening.

FUEL PRESSURE

Note. If vehicle starts and runs, fuel pump main relay is okay.

Spark

Check for spark at secondary coil wire and each spark plug wire using a spark tester. If spark is not present, continue with following tests. Check spark plug wire resistance on suspect wires. Resistance should be less than 25,000 ohms.

Ignition Coil Power Source

  1. Disconnect ignition coil primary leads. Turn ignition on. Using voltmeter, check voltage between ground and Black/Yellow wire terminal of ignition coil harness.
  2. Battery voltage should be present. If battery voltage is not present, check for open in Black/Yellow wire between coil and ignition switch.

Ignitor Power Source

Turn ignition off. Disconnect harness connector at distributor. Turn ignition on. Using voltmeter, check for battery voltage between ground and Black/Yellow wire of harness. If voltage is not present, check for open in Black/Yellow wire between ignition coil and harness connector. If wire is okay, check ignition coil resistance (for internal short to ground).

Ignitor Check

Check TDC/CRANK/CYL sensor resistance values. See TACH PULSE SIGNAL . Check power sources. If no problems are found and spark is not present, replace ignitor.

Scheme 56

Scheme 56: Ignition Coil Resistance
Scheme 56: Ignition Coil Resistance
  1. Remove primary and secondary leads from ignition coil. Using an ohmmeter, check resistance between primary terminals "A" and "B" of ignition coil. (Scheme 56) Resistance should be.6-.8 ohm at room temperature.
  2. Check secondary resistance between terminal "A" and secondary output terminal (coil tower). See «IGNITION COIL RESISTANCE»(ref-15814-S08702711872001010800000) table. Check for continuity between terminals "A" and "C". Continuity should exist. If readings are not within specification, replace coil. IGNITION COIL RESISTANCE - Ohms @ 68°F (20°C) Application Primary Secondary Prelude.6-.8 14,000-22,000

Scheme 57

Scheme 57: Tach Pulse Signal
Scheme 57: Tach Pulse Signal

Scheme 58

Scheme 58
Scheme 58
  1. Timing control and triggering of fuel injectors are based upon input signals from TDC/CRANK/CYL sensors. These sensors are simple Permanent Magnet (PM) generator pick-up coils.
  2. Using a DVOM on low voltage scale (preferably with a bar-graph function), check for a pulsed low-voltage signal at proper Engine Control Module (ECM) harness terminals with engine cranking. See «WIRING HARNESS & SENSOR RESISTANCE TEST»(ref-15814-S04786075822001010800000) table. (Scheme 57) If a pulsed signal is present, fault does not exist. If pulsed signal is not present, check sensor and wiring integrity.
  3. To test sensor and wiring integrity, turn ignition off. Disconnect connectors from ECM. Lightly probe appropriate ECM harness terminals to check for proper winding resistance of each sensor. See «WIRING HARNESS & SENSOR RESISTANCE TEST»(ref-15814-S04786075822001010800000) table. If resistance is within specification, go to step 5). If resistance is not within specification, go to next step.
  4. Check resistance of TDC/CRANK/CYL sensor directly at sensor connector. (Scheme 58) See «TDC/CRANK/CYL SENSOR RESISTANCE TEST»(ref-15814-S05712418282001010800000) table. If sensor resistance is within specification, repair open, short or corrosion in wire harness between sensor(s) and ECM. If resistance is not within specification, replace sensor.
  5. Check continuity to ground at each ECM sensor terminal. If continuity is not present, replace distributor housing. If continuity is present, go to next step.
  6. Disconnect sensor(s) and recheck for continuity to ground at ECM harness sensor terminals. If continuity no longer exists, go to next step. If continuity to ground is still present, repair short to ground in ECM harness between ECM and sensor(s).
  7. Check continuity to ground on each sensor connector terminal. See «TDC/CRANK/CYL SENSOR RESISTANCE TEST»(ref-15814-S05712418282001010800000) table. (Scheme 58) Continuity should not exist. If continuity to ground exists, replace sensor. WIRING HARNESS & SENSOR RESISTANCE TEST Application Terminals Ohms CRANK B15 & B16 350-700 CYL B11 & B12 350-700 TDC B13 & B14 350-700 TDC/CRANK/CYL SENSOR RESISTANCE TEST Application Terminals Wire Color CRANK Sensor Wire 1 Of 2 "B" Blue/Green 2 Of 2 "F" Blue/Yellow CYL Sensor Wire 1 Of 2 "D" Orange 2 Of 2 "H" White TDC Sensor Wire 1 Of 2 "C" Orange/Blue 2 Of 2 "G" White/Blue

IDLE SPEED & IGNITION TIMING

Ensure idle speed and ignition timing are set to specification. See IDLE SPEED SPECIFICATIONS and IGNITION TIMING tables. For adjustment procedures, see ADJUSTMENTS article in the ENGINE PERFORMANCE Section.

ApplicationRPM
Prelude (1)500-600
(1) With Electronic Air Control Valve (EACV) disconnected, headlights and cooling fan off and transmission in Neutral or Park.
(1)With Electronic Air Control Valve (EACV) disconnected, headlights and cooling fan off and transmission in Neutral or Park.

IDLE SPEED SPECIFICATIONS

Application(1) Specification
Prelude13-17 @ 650-750
(1) Ignition timing is controlled by the Engine Control Module (ECM) and cannot be adjusted.
(1)Ignition timing is controlled by the Engine Control Module (ECM) and cannot be adjusted.

IGNITION TIMING (Degrees BTDC @ RPM)

SUMMARY

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to G -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.

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