Engine Control System - Basic Diagnostic Procedures: Diagnosis Pontiac Vibe I

VISUAL INSPECTION

Note. Several of the symptom procedures call for a careful visual/physical check. DO NOT neglect to perform the visual/physical check. The visual/physical check is an important procedure that can lead to the correction of a concern without further diagnosis. The performance of the visual/physical check can save valuable time.

Inspect all the PCM grounds for secure and clean connections that are in the proper location. Check all vacuum hoses for splits, kinks, and proper connections and routing, as shown on the vehicle emission control information label. Check for air leaks at throttle body mounting area and intake manifold sealing surfaces. Inspect the wiring harness for proper connections and damage. Visually inspect all electrical wiring. Look for chafed, stretched, cut or pinched wiring. Check the vacuum hoses thoroughly for any type of leak or restriction. Inspect the air inlet ducts for collapsed or restricted sections. If necessary, see VACUUM DIAGRAMS - VIBE article to verify routing and connections. Inspect air induction system for possible vacuum leaks. Repair as necessary. If vehicle has a no-start condition, go to NO-START DIAGNOSIS .

MECHANICAL INSPECTION

Cylinder Leakage Test

The combustion pressure leakage test provides an accurate means for determining engine condition. Combustion pressure leakage testing will detect exhaust and intake valve leaks (improper seating), leaks between adjacent cylinders or into water jacket, or any causes for combustion/compression pressure loss.

Check the coolant level and fill as required. Do not install the radiator cap. Start and operate the engine until it attains nor operating temperature, then turn the engine off. Remove the oil filler cap. Remove the air cleaner.

Calibrate the tester according to the manufacturer's instructions. The shop air source for testing should maintain 70 psi (483 kPa) minimum and 200 psi (1379 kPa) maximum. 80 psi (552 kPa) is recommended.

High cylinder leakage may indicate one or more of the following

1. Worn or burnt valves.
2. Broken valve springs.
3. Stuck valve lifters.
4. Incorrect valve lash/adjustment.
5. Damaged piston.
6. Worn piston rings.
7. Worn or scored cylinder bore.
8. Damaged cylinder head gasket.
9. Cracked or damaged cylinder head.
10. Cracked or damaged engine block.

1. Disconnect negative battery cable.
2. Remove engine cover from engine. Remove 4 ignition coils from the cylinder head cover. Remove the spark plugs.
3. Rotate the crankshaft to place the piston in the cylinder being tested at Top Dead Center (TDC) of the compression stroke.
4. Install Cylinder Head Leakdown Tester (J 35667), or equivalent.
5. Apply shop air pressure to the leakdown tester and adjust according to the manufacturers instructions.
6. Record the cylinder leakage value. Cylinder leakage that exceeds 25 percent is considered excessive and may require component service. In excessive leakage situations, inspect for the following conditions: Air leakage sounds at the throttle body or air inlet hose that may indicate a worn or burnt intake valve or a broken valve spring. Air leakage sounds at the exhaust system tailpipe that may indicate a worn or burnt exhaust valve or a broken valve spring. Air leakage sounds from the crankcase, oil level indicator tube, or oil fill tube that may indicate worn piston rings, a damaged piston, a worn or scored cylinder bore, a damaged engine block or a damaged cylinder head. Air bubbles in the cooling system may indicate a damaged cylinder head or a damaged cylinder head gasket.
7. Perform the leakage test on the remaining cylinders and record the results.

Diagnosis

1. Remove Heated Oxygen Sensor (HO2S) in front of catalytic converter. Install Backpressure Tester (J 35314-A) in place of HO2S. Start engine and allow it to reach normal operating temperature. Record the exhaust system backpressure reading. If backpressure does not exceed 1.25 psi (8.6 kPa), go to next step. If backpressure is more than 1.25 psi (8.6 kPa), go to step 3 .
2. Increase engine speed to 2000 RPM and note backpressure. If reading exceeds 1.25 psi (8.6 kPa), go to next step. If reading does not exceed 1.25 psi (8.6 kPa), go to step 6 .
3. Turn ignition switch to OFF position. Remove backpressure gauge and install HO2S. Remove post-catalyst HO2S and install backpressure gauge. Start engine and let idle. Note backpressure. Increase engine speed to 2000 RPM and note backpressure. If reading exceeds 1.25 psi (8.6 kPa), go to next step. If reading does not exceed 1.25 psi (8.6 kPa), go to step 5 .
4. Check exhaust system for collapsed pipe, debris, heat distress, 2-layer exhaust pipe separation and possible internal muffler internal failure. Replace as necessary. After repair, go to 6 .
5. Replace catalytic converter. After repair, go to next step.
6. Remove the backpressure gauge and reinstall the HO2S sensor. Clear DTCs. Road test the vehicle in order to verify the repair.

Diagnostic Aids

Inspect for any of the following conditions

1. Insufficient fuel can cause a no-start condition. Thoroughly inspect the fuel delivery system for sufficient fuel volume to the fuel injectors. Inspect the fuel supply components for partial blockage or restrictions.
2. Fuel injectors with partially blocked and restricted nozzles, or a malfunctioning solenoid, can cause a no-start condition. See «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL»(ref-152779-S08897027942003022500000) and «FUEL INJECTOR COIL TEST - ENGINE COOLANT TEMP»(ref-152779-S06830036892003022500000) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTS - 1.8L VIBE article.
3. There may be fuel spray at the fuel injectors and the indicated fuel pressure may be correct, yet there may not be enough fuel to start the engine. If the fuel injectors and the injector circuits are OK, and fuel spray is detected, the fuel injector ON time may be inadequate. If the PCM receives incorrect inputs from the various information sensors, the fuel delivered by the fuel injectors may be inadequate to start the engine. Check all the engine data parameters with a scan tool and compare the values indicated with the expected values or the values from a known-good vehicle.
4. Check the Crankshaft Position (CKP) sensor engine reference signal with a scan tool. Observe the Engine Speed parameter while cranking the engine. The scan tool should indicate a steady 200-300 RPM while cranking. If erratic values, such as sudden spikes in the engine speed are displayed, the engine reference signal is not stable enough for the engine to start and run properly.
5. An intermittent condition of cranks but will not start or the engine quits while running can be caused by a PCM shutdown. There will be no fuel, spark, or data communications during a PCM shutdown. A short to ground in the 5-volt reference circuit of the engine data sensors will cause a PCM shutdown. When the short to ground is absent, the PCM will operate normally with no DTCs stored. Test for a shorted Throttle Position (TP) or Fuel Tank Pressure (FTP) sensor, or shorted sensor wiring.
6. Inspect the engine electrical ground points G104 and G105, if the engine has no spark and no fuel injector pulse with no DTCs.
7. If the engine almost starts and then stalls, check for an open in the ground circuits of the CKP sensor and the Camshaft Position (CMP) sensor.
8. Water or foreign material in the fuel can cause a no-start or engine will not stay running condition. During freezing weather water can freeze inside the fuel system. The engine may start after 30 minutes in a heated repair shop. The malfunction may not recur until parked overnight in freezing temperatures. Extreme weather conditions can cause contaminated fuel to prevent the vehicle from starting.
9. A vehicle that starts and runs after being brought to the repair shop for a no-start complaint, may have an ignition system that is susceptible to moisture. Spray water on the ignition system components and the wiring in order to check for an engine starting or will not stay running concern.

An intermittent malfunction may be caused by fault in any of the critical information or component electrical circuits. Inspect the wiring harness and the components for an intermittent condition. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 1.8L VIBE article. Repair any electrical circuit faults found.

FUEL PRESSURE TEST

Note. For information on testing individual fuel system components, see FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 1.8L VIBE article.

Ignition System Diagnosis

Note. If DTCs P1300, P1305, P1310, or P1315 are set, diagnose these DTCs first. See SELF-DIAGNOSTICS - 1.8L VIBE article.

For Ignition System Diagnosis, see IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 1.8L VIBE article.