Engine diagnostics performed during operation (Mitsubishi Colt 4)

Increased content of harmful substances in exhaust gases

Measurements show high concentrations of harmful substances; a rotten egg smell may occur. The appearance of an unpleasant smell is not necessarily a sign of improper combustion.

Perform circuit diagnostics. Check:

• no leaks in vacuum lines;
• cooling system and fan;
• remove carbon deposits using engine cleaner.

If high NOx concentrations are detected during measurements, check for reasons why the fuel mixture is too lean or the combustion temperature is below normal.

If high concentrations of hydrocarbons and CO are detected during measurements or the exhaust has an unpleasant odor, check for reasons why the working mixture is too rich. These include:

• deviation of fuel pressure from the norm (fuel pump);
• clogging or sticking of the positive crankcase ventilation valve or clogging of the system hose;
• incorrect installation of spark plugs, spark plug wires or ignition system components;
• incorrect ignition timing;
• incorrect installation of the fuel tank cap.

Self-ignition in cylinders

The engine continues to run after the ignition is turned off, but very unevenly. If the engine runs smoothly, check the ignition switch and ignition adjustment:

• Inspect the spark plugs;
• Adjust the ignition timing;
• Injection engines:
• check the injector for leaks;
• apply 12V to the fuel pump test terminal to turn it on. Raise the fuel system pressure;
• inspect the injector and throttle body for fuel leaks.

Backfires

Fuel ignition in the intake manifold or in the exhaust system with a loud noise. Check:

• ignition coil output voltage;
• ignition order, paying attention to the distributor cap, spark plug wires, their correct installation;
• setting the ignition timing;
• serviceability of spark plugs, spark plug wires and boots.

Check compression (check for sticking or loose valves).

Check the valve timing.

Interruptions, dips, jerking

A short-term loss of engine sensitivity to pressing the gas pedal can occur at any speed. Usually most pronounced when trying to start moving after stopping. In severe cases, it can lead to engine stalling.

Check:

• fuel pressure (fuel pump);
• fuel for the presence of water;
• setting the ignition timing;
• generator output voltage The generator requires repair if the voltage is below 9 V or above 16 V;
• to break the connection line to the ignition system ground.

Skipping Flashes

Constant jerking noise when the engine is running, usually increasing as the engine load increases. The exhaust pipe constantly makes splashing noises when idling or at low speeds.

Conduct a thorough inspection. If you suspect that the misfires at idle and while driving are caused by a malfunction of the ignition system, perform the appropriate checks.



Identify the non-working cylinder. To do this:

• Start the engine. Disconnect the idle air supply system actuator. Using the appropriate tool, disconnect one spark plug wire at a time.
• A drop in engine speed of approximately 50 rpm may occur when disconnecting the spark plug wire from each cylinder, followed by uneven engine operation and even stalling. Turn off the engine, connect the idle air supply system drive.
• If, when disconnecting the spark plug wire from one or more cylinders, there is no drop in the rotation speed or no significant difference in the degree of drop in the rotation speed is observed, then check the suspected cylinder (cylinder(s)) for spark discharges using the appropriate device. If there is a discharge, then unscrew the spark plug from this cylinder and check for the presence of: cracks, wear, incorrect gap, burning of electrodes, significant deposits.

Check the spark plug wire resistance (resistance should not exceed 30,000 ohms).

If the previous checks did not produce results, perform the following checks:

• inspect the ignition system for moisture, dust, and burning. Spray the spark plug wires with water mist to detect short circuits;
• check the fuel system clogged fuel filter, presence of water in fuel, low pressure;
• check the compression;
• check the valve timing.

Low fuel efficiency

Fuel economy measured in real world road test conditions is significantly lower than expected. Also, fuel economy is significantly lower than the previous ton this car had under the same conditions. Check:

• thermostat for valve malfunction (constantly open) or deviation from the set temperature range;
• fuel pressure.

Please check:

• vacuum hoses for cracks, kinks and loose fittings;
• tire pressure;
• mass of transported goods;
• use when driving with excessive or frequent acceleration.

Perform electrical circuit diagnostics.

Check the air filter for contamination.

Check the speedometer calibration.

Check the spark plug wires for cracks, hardening, and correct connection.

Check the ignition timing.

Remove the spark plugs, check for contamination and cracks, wear, gap changes, electrode burnout and significant deposits. Replace if necessary.

Check the compression.

Check the brakes for drag.

Recheck the fuel consumption with the tank filled with fuel.

Check for deposits in the exhaust system.

Uneven operation and engine stalling at idle

The engine runs unevenly at idle. In more serious cases, the car may vibrate. It is also possible that the rotation speed changes (oscillations). In this case, the engine may stop. Deviation from the normal rotation speed is possible.
Check:

• setting the ignition timing;
• compliance of the resistance of the sensor coil and contacts with the norm;
• injector for leaks;
• lack of loose connections of the ignition coil;
• no moisture under the distributor cap;
• absence of contamination and cracks in spark plugs, wear, gap changes, electrode burning and significant deposits.

RPM fluctuations and/or popping noises in the muffler

Engine power fluctuations at a constant throttle opening at idle or when driving Subjectively felt as acceleration and deceleration of the car without changing the position of the gas pedal.



Check:

• setting the ignition timing,
• fuel filter on the fuel line for contamination and deposits;
• fuel pressure;
• generator output voltage needs repair if the voltage is below 9 V or above 16 V.

Check the CO content in the exhaust gases using a suitable device. If the CO content is too low (below 0.3%), the fuel-air mixture is lean.

This causes the car to be difficult to control. Remove the spark plugs. Check for dirt and cracks, wear, gap changes, electrode burnout, and significant deposits. Also check the condition of the entire ignition system.

Loss of power, engine sluggishness, poor response to accelerator pedal input

The power developed by the engine is lower than expected. Complete or almost complete insensitivity of the car to partial pressing of the gas pedal.

Remove the air cleaner and check the air filter for contamination. Replace if necessary.

Check:

• setting the ignition timing;
• presence of contamination in the fuel filter and deviations of fuel pressure from the norm;
• the state of the line connecting the control unit to the engine ground.

Check the exhaust system for obstructions. To do this, do the following:

• with the engine running and at normal temperature, connect the vacuum gauge to any suitable vacuum port in the intake manifold. Measure the vacuum at 1000 rpm;
• slowly increase the speed to 2500 rpm. Measure the vacuum when the speed is stable at 2500 rpm;
• if the vacuum level at 2500 rpm decreases by more than 21 kPa compared to the value measured at 1300 rpm, check the exhaust system for obstructions;
• disconnect the exhaust pipe from the engine and perform the procedures specified in the previous paragraphs. If the vacuum still drops by more than 21 kPa, check the valve installation.

Check the generator output voltage. The generator requires repair if the voltage is below 9 V or above 16 V.



Check engine valve timing and compression.

Check the camshaft for wear.

Check the ignition voltage with a suitable device.

Engine detonation

A moderate to severe knocking noise that usually gets worse with acceleration. A sharp metallic sound that changes as the throttle is opened.

Check for overheating. Overheating can be caused by:

• low coolant level;
• loosening of the coolant pump belt;
• restricted air or coolant flow through the radiator;
• faulty thermostat;
• faulty electric fan circuit;
• changes in the sensitivity of the coolant temperature sensor.

Check:

• fuel quality, its octane number;
• correct selection of spark plugs according to thermal conditions;
• setting the ignition timing;
• fuel system pressure (is there a drop);
• fuel system;
• correct adjustment of the gear shift system;
• correct selection of engine parts, such as camshaft, head, pistons, etc.

Remove carbon deposits using engine cleaner. Instructions for use are provided on the packaging.

Increased oil consumption

Increased oil consumption may be caused by one of the following reasons:

• leak in lubrication system;
• incorrect determination of the oil level using the dipstick (When determining the oil level, place the car on a level surface and wait for some time for the oil to drain into the crankcase);
• idle speed too low;
• worn out oil pump;
• dirty oil filter;
• the mesh filter on the oil pump inlet pipe has become loose or clogged;
• incorrect oil viscosity or thin oil;
• long periods of driving at high speeds or with a trailer usually results in increased oil consumption;
• malfunction in the forced crankcase ventilation system;
• wear of valve stem seals and/or valve guides;
• poorly ground, worn or broken piston rings;
• incorrect piston installation or incorrect size.

Low oil pressure

Low oil pressure can be caused by the following reasons:

• excessive clearance in crankshaft bearings;
• cracks, pores or plugs in the cylinder block channels;
• absence or incorrect installation of the lubrication system plug;
• idle speed too low.

Noise in the valve train

Noise in the valve train may be caused by any of the following reasons:

• low oil pressure;
• broken valve springs, valve sticking;
• worn, dirty or faulty valve lifters;
• worn or defective timing shaft.

Knocking in a cold engine, lasting two to three minutes and/or increasing with increasing load

The flywheel is touching the casing. Adjust the casing installation.

Increased clearance between pistons and cylinders. Rebore the block cylinders and hone to the repair size. Replace the piston. Piston knocking on a cold engine usually disappears after the engine warms up. Piston knocking on a cold engine that disappears after 1-2 minutes is acceptable.

Bent connecting rod.

A loud knocking noise from a warm engine that occurs under load

• Pulley hub failure;
• Belt too tight. Replace or adjust tension;
• The exhaust pipe touches the road surface;
• Crack in the flywheel;
• Increased clearance in main bearings;
• Increased clearance in connecting rod bearings.

A light knock from a warm engine

Detonation Check fuel quality. Check ignition timing.

Exhaust manifold leak. Tighten bolts and/or replace gasket.

Increased clearances of connecting rod bearings. Replace bearings if necessary.

Knocking noises when starting the engine, lasting only a few minutes

Oil of the wrong viscosity. Fill with oil of the viscosity corresponding to the operating conditions.



Increased axial clearance of the crankshaft - replace the thrust bearing (half rings).

Excessive clearance in main bearings. Replace worn parts.

Knocking noises on a warm engine at idle

Poor belt tension or wear.

Generator bearing.

Gas distribution mechanism.

The viscosity of the engine oil does not meet the requirements. Fill in oil with a viscosity that corresponds to the season of operation of the vehicle.

Piston pin clearance too large. Replace piston pin and piston.

Connecting rod adjustment. Check clearances and replace the connecting rod if necessary.

Insufficient clearance between cylinders and piston. Hone the cylinder and fit a new piston.

The piston pin is offset from the axis to the other side. Install the piston correctly.

The engine gets very hot

Engine cooling system leaks. Check the expansion tank, hoses and radiator.

The belt is slipping or damaged. Replace the belt if necessary.

Thermostat stuck in closed position. Check and replace if necessary.

Leaking cylinder head gasket. Check and repair if necessary.

The electric radiator fan does not work.