Increased content of harmful substances in exhaust gases
Measurements give high concentrations of harmful substances; There may be a smell of rotten eggs. The appearance of an unpleasant odor is not necessarily a sign of improper combustion.
Run circuit diagnostics. Check:
- lack of suction in vacuum lines;
- cooling system and fan;
- remove carbon deposits with engine cleaner.
If high NOx concentrations are detected during measurements, check for reasons why the mixture is too lean or the combustion temperature is too low.
If high concentrations of hydrocarbons and CO are detected during measurements, or the exhaust has an unpleasant smell, check the reasons why the mixture is too rich. These include:
- abnormal fuel pressure (fuel pump);
- sticking or clogging of the valve of the forced crankcase ventilation system or clogging of the system hose;
- improper installation of spark plugs, spark plug wires or components of the ignition system;
- incorrect ignition timing;
- improper 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, then check the ignition switch.
Examine the spark plugs.
Adjust ignition timing.
Check the injector for leakage;
Apply 12V to the fuel pump test terminal to turn it on. Raise the pressure in the fuel system;
Inspect the injector and throttle body for fuel leaks.
Back flashes
Ignition of fuel in the intake manifold or in the exhaust system with a loud sound.
Check:
- ignition coil output voltage;
- ignition order, paying attention to the distributor cap, spark plug wires, their correct laying;
- setting the ignition moment;
- serviceability of spark plugs, spark plug wires and covers.
Check compression (detection of stuck or loose valves).
Check the valve timing setting.
Interruptions, failures
A short-term loss of engine sensitivity to pressing the gas pedal can occur at any speed. Usually most strongly manifested when trying to start moving after stopping. In severe cases, it can lead to engine shutdown.
Check:
- fuel pressure (fuel pump);
- fuel for the presence of water;
- setting the ignition moment;
- generator output voltage. The alternator requires repair if the voltage is below 9V or above 16V;
- to break the connection line to «mass» ignition systems.
Skip flashes
Constant jolts during engine operation, usually increasing with increasing engine load. The exhaust pipe constantly makes splashing sounds at idle or at low speeds.
Conduct a thorough inspection. If you suspect that misfiring at idle and while driving is caused by a malfunction in the ignition system, perform the appropriate checks.
Determine the idle cylinder. For this:
- Start the engine. Disconnect the idle air supply actuator. Using the appropriate tool, disconnect one spark plug wire at a time.
- Possible drop in speed when disconnecting the spark plug wire from each cylinder (about 50 rpm) with subsequent uneven operation of the engine and even a stop. Stop the engine, connect the idle air supply actuator.
- If there is no drop in speed when the spark plug wire is disconnected from one or more cylinders, or there is no significant difference in the degree of drop in speed, then the suspect cylinder (cylinders) check for sparks with a suitable instrument. If there is a discharge, then unscrew the spark plug from this cylinder and check for cracks, wear, incorrect clearance, burning of the electrodes, and significant deposits.
Check spark plug resistance (resistance should not exceed 30,000 ohms).
If the previous checks have failed, perform the following checks:
- inspect the ignition system for moisture, dust, burning. Spray spark plug wires with water mist to check for shorts;
- check the fuel system (clogged fuel filter, presence of water in fuel, low pressure);
- check compression;
- check the correct installation of the spark plug wires.
Poor fuel economy
Fuel economy, measured in real road test conditions, is significantly lower than expected. In addition, the fuel efficiency is significantly lower than what this car used to have in the same conditions.
Check:
- thermostat for valve failure (permanently open) or deviation from the specified temperature range;
- fuel pressure.
Check:
- vacuum hoses for cracks, kinks and loose fittings;
- tire pressure;
- the mass of transported goods;
- application when driving too large or frequent accelerations.
Perform electrical circuit diagnostics.
Check the air filter for dirt.
Check speedometer calibration.
Check the spark plug wires for cracks, hardening, correct connection,
Check ignition timing.
Unscrew the spark plugs, check for dirt and cracks, wear, gap changes, burnt electrodes and significant deposits. Replace if necessary.
Check compression.
Check the brakes for sticking.
Re-check the fuel consumption with the tank filled with fuel.
Check for deposits in the exhaust system.
Uneven operation and stop of the engine idling
The engine runs unevenly at idle. In more serious cases, the vehicle may vibrate. It is also possible to change the speed (fluctuations). This does not prevent the engine from stopping. Deviation from normal speed is possible.
Check:
- setting the ignition moment;
- compliance of the resistance of the sensor coil and contacts with the norm;
- injector for leaks;
- lack of loose connections of the ignition coil;
- lack of moisture under the distributor cap;
- absence of pollution and cracks in spark plugs, wear, change in gap, burning of electrodes and significant deposits.
RPM fluctuations and/or muffler pops
Fluctuations in engine power at a constant degree of throttle opening at idle or while driving are subjectively felt as acceleration and slowing down of the car without changing the position of the gas pedal.
Check:
- setting the ignition moment;
- fuel filter on the gas line for contamination and deposits;
- fuel pressure;
- generator output voltage (repair is needed in case the voltage is lower than 9 V or higher than 16 V).
Check the CO content in the exhaust gases with a suitable instrument. If the CO content is too low (below 0.3%), the air-fuel mixture is lean. This leads to difficulties with the controllability of the car.
Unscrew the spark plugs. Check for fouling and cracking, wear, gap changes, burnt electrodes, and significant deposits. Also check the condition of the entire ignition system.
Loss of power, engine inertia, poor response to pressing the pelvis pedal
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 degree of contamination of the air filter. Replace if necessary.
Check:
- setting the ignition moment;
- the presence of contaminants in the fuel filter and fuel pressure deviations from the norm;
- state of the lines connecting the control unit to «mass» engine.
Check the exhaust system for obstructions. To do this, do the following:
- with the engine running and operating at normal temperature, connect a vacuum gauge gauge to any suitable vacuum port in the intake manifold. At a speed of 1000 rpm, measure the vacuum:
- slowly increase the speed to 2500 rpm. Measure the vacuum at a stable speed level of 2500 rpm;
- if the vacuum level at 2500 rpm drops by more than 21 kPa against the value measured at 1000 rpm, check the exhaust system for interference;
- disconnect the exhaust pipe from the engine and carry out the procedures indicated in the previous paragraphs. If the vacuum still drops more than 21 kPa, check the valve setting.
Check generator output voltage. The alternator requires repair if the voltage is below 9V or above 16V.
Check engine valve setting and compression.
Check the camshaft for wear.
Check the ignition voltage with a suitable instrument.
Detonation in the engine
Knocking, moderate to severe, usually worse with acceleration. Harsh metallic sound that changes when the throttle is opened.
Check if there is overheating. Overheating may be due to:
- low coolant level;
- loosening the coolant pump belt;
- limited 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;
- the correct selection of spark plugs according to the thermal regime;
- setting the ignition moment;
- fuel system pressure (is there a fall);
- fuel system;
- correct adjustment of the gear shift system;
- correct selection of engine parts, such as camshaft, head, pistons, etc.
Remove carbon deposits with engine cleaner. Instructions for use are given on the packaging.
Increased oil consumption
Increased oil consumption can be caused by one of the following reasons:
- leakage of the lubrication system. Tighten threaded connections and/or replace, if necessary, gaskets and seals;
- incorrect determination of the oil level using the oil feet on the dipstick. When checking the oil level, park the vehicle on a level surface and wait a while for the oil to drain into the crankcase.
- too low idle speed. If the engine idle speed is not controlled by the electrical unit, adjust the idle speed as required;
- worn out oil pump. Replace oil pump;
- dirty oil filter. Replace oil filter;
- the mesh filter on the oil pump intake pipe is unscrewed or clogged. Clean and rinse the strainer.
- inappropriate oil viscosity or diluted oil;
- long driving at high speeds or with a trailer usually leads to increased oil consumption;
- malfunction in the forced crankcase ventilation system;
- wear of valve stem seals and/or valve guides;
- Badly lapped, worn or broken piston rings. Let the new piston rings break in for a while. If necessary, replace broken or worn piston rings;
- wrong piston installation or wrong size.
Low oil pressure
Low oil pressure can be caused by the following reasons:
- excessive clearance in the crankshaft bearings. Replace bearings if necessary;
- cracks, pores or plugs in the channels of the cylinder block. Repair or replace the unit;
- missing or incorrect installation of the lubrication system plug. Install plugs or replace if necessary;
- too low idle speed. Adjust idle speed as required.
Noise in the gas distribution mechanism
Noise in the gas distribution mechanism can be caused by any of the following reasons:
- low oil pressure. Eliminate the cause;
- breakage of valve springs, jamming of valves;
- worn, dirty or defective valve lifters. Remove dirt, check and, if necessary, replace;
- worn or defective timing shaft. Replace shaft.
Knocking in a cold engine that lasts two to three minutes and/or gets worse with increasing load
- The flywheel touches the casing. Adjust the shroud.
- Increased clearance between pistons and cylinders. Bore the block cylinders and honing to the repair size. Replace piston. Piston knock on a cold engine usually disappears after the engine warms up. Piston knocking from a cold engine, which disappears after 1-2 minutes, is acceptable.
- Bent rod.
Strong knocking of a warm engine that occurs under load
- Pulley hub failure. Replace if necessary.
- The belt is too tight. Replace or adjust tension.
- The exhaust pipe touches the road surface. Fix the exhaust pipe.
- Crack in the flywheel.
- Increased clearance in main bearings. Replace if necessary. Increased clearance in connecting rod bearings. Replace if necessary.
Slight warm engine noise
- Detonation. Check fuel quality. Check the ignition setting.
- Exhaust manifold leakage. Tighten bolts and/or replace gasket.
- Increased clearances of connecting rod bearings. Replace bearings if necessary.
Knocking when starting the engine, lasting only a few minutes
- Oil of the wrong viscosity. Fill with oil of a viscosity suitable for operating conditions.
- Increased axial clearance of the crankshaft. Replace thrust bearing (semirings).
- Excessive clearance in main bearings. Replace worn parts.
Knocking on a warm engine at idle
- Poor belt tension or wear. Tighten and/or replace if necessary.
- Generator bearing. Replace if necessary.
- Gas distribution mechanism. Replace parts if necessary.
- The viscosity of the engine oil does not meet the requirements. Fill with oil with a viscosity appropriate for the season of operation of the car,
- Piston pin clearance too large. Replace piston pin and piston.
- Incorrect crank adjustment. Check clearances and replace connecting rod if necessary.
- Insufficient clearance between cylinders and piston. Honed 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
- Leakage in the engine cooling system. Check expansion tank, hoses and radiator.
- The belt is slipping or damaged. Replace belt if necessary.
- Thermostat stuck in closed position. Check and replace if necessary.
- Leaking through the cylinder head gasket. Check and, if necessary, correct.
- The electric radiator fan does not work.