Engine diagnostics performed during operation (Nissan Murano Z50)

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 odor 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 an engine cleaner.

If high NOx concentrations are detected during measurements, check for reasons why the working 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);

♦ jamming or clogging of the positive crankcase ventilation system valve or clogging of the system hose;



♦ Incorrect installation of spark plugs 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

• Inspect the spark plugs.
• Apply 12V to the fuel pump test terminal to turn it on. Increase the pressure in the fuel system.
• Inspect the injectors for fuel leaks.

Reverse flashes

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

Check:

♦ output voltage of ignition coils;

♦ ignition order, paying attention to the ignition coil wires and their correct installation;

♦ setting the ignition timing;

♦ serviceability of spark plugs.

• Check the compression (detection of sticking or loose valves).
• Check the valve timing.

Interruptions, dips, jerking

A temporary loss of engine sensitivity to pressing the gas pedal can occur at any speed. Usually most noticeable 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 during engine operation, usually increasing with increasing engine load. The exhaust pipe constantly makes a splashing sound when idling or at low speeds

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

• Identify the non-working cylinder.

To do this, you need to contact a service station.

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

♦ inspect the ignition system for moisture, dust, and burns,

♦ Check the fuel system (clogged fuel filter, presence of water in fuel, low pressure);

♦ check compression;

♦ Check the valve timing.

Low fuel efficiency

Fuel economy measured in real-world road test conditions is significantly lower than expected. In addition, fuel efficiency is significantly lower than what the car previously achieved under the same conditions

Check:

♦ thermostat for valve malfunction (always open) or deviation from the specified temperature range;

♦ fuel pressure.

Please check:

♦ vacuum hoses for cracks, kinks and loose fasteners;

♦ tire pressure;

♦ mass of transported cargo;

♦ applying excessively high or frequent accelerations while driving.

• Perform diagnostics of electrical circuits.
• Check the air filter for contamination.
• Check the speedometer calibration.
• Check the ignition timing.
• Remove the spark plugs and check for contamination, cracks, wear, gap changes, electrode burns, and significant deposits. Replace if necessary.
• Check the compression.
• Check the brakes for drag.
• Recheck the fuel consumption with the fuel tank filled with fuel.
• Check for deposits in the exhaust system.

Uneven operation and stalling of the engine at idle

The engine runs unevenly at idle. In more serious cases, vehicle vibration may occur. Changes in rotational speed (oscillations) are also possible. This may lead to engine stalling. Deviation from normal rotation speed is possible

Check:

♦ setting the ignition timing;



♦ injectors for leaks;

♦ absence of loose connections of ignition coils;

♦ absence of contamination and cracks in spark plugs, wear, gap changes, electrode burning and significant deposits.

RPM fluctuations and/or popping sounds in the muffler

Fluctuations in engine power at a constant throttle opening degree at idle or while driving. Subjectively felt as acceleration and deceleration ("jerks") of the car without changing the position of the gas pedal

Check:

♦ setting the ignition timing;

♦ Check the fuel filter on the fuel line for contamination and deposits;

♦ fuel pressure;

♦ generator output voltage (repair is required 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 air-fuel mixture is lean.

This leads to difficulties in controlling the vehicle.

• Remove the spark plugs. Check for contamination, cracks, wear, gap changes, electrode burns 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 degree of contamination of the air filter. Replace if necessary.
• Check:

♦ setting the ignition timing;

♦ presence of contamination in the fuel filter and deviation of fuel pressure from the norm;

♦ condition of the lines 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 sensor to any suitable vacuum port in the intake manifold. Measure the vacuum at 1000 rpm;

♦ Slowly increase the engine speed to 2500 rpm. Measure the vacuum when the engine 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 1000 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 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 knocking noise, ranging from moderate to loud in intensity, usually increasing in intensity with acceleration. A sharp metallic sound that changes when the throttle valve is opened

• Check for overheating. Overheating may be due to:

♦ 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 the thermal conditions,'*

♦ setting the ignition timing;



♦ fuel system pressure (is there a fall?);

♦ fuel system;

♦ correct selection of engine parts, such as camshaft, head, pistons, etc.

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

Increased oil consumption

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

♦ leakage in the lubrication system;

♦ incorrect determination of the oil level using the oil dipstick, (When checking the oil level, place the vehicle on a level surface and wait a while for the oil to drain into the crankcase.)

♦ idle speed too low;

♦ worn oil pump;

♦ dirty oil filter;

♦ the mesh filter on the oil pump inlet pipe is loose or clogged;

♦ Incorrect oil viscosity or diluted oil;

♦ Long-term 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;

♦ 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 the 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 can 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

♦ Increased clearance between pistons and cylinders. Bore 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. A knocking sound from the pistons of a cold engine that disappears after 1-2 minutes is acceptable.



♦ Bent connecting rod.

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

♦ Pulley hub failure.

♦ The belt is too tight. Replace or adjust tension.

♦ The exhaust pipe touches the road surface.

♦ Increased clearance in main bearings.

♦ Increased clearance in connecting rod bearings.

A light knock from a warm engine

♦ Detonation. Check fuel quality. Check the 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 incorrect viscosity. Fill with oil of a viscosity appropriate for operating conditions.

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

♦ Excessive clearance in main bearings. Replace worn parts.

Knocking noise 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 with oil with a viscosity that matches the season of vehicle operation.

♦ Too much clearance in the piston pin. Replace the piston pin and piston.

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

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

♦ The piston pin is displaced from the axis in the other direction. Install the piston correctly.

The engine gets very hot

♦ Leakage in the engine cooling system. Check the expansion tank, hoses and radiator.



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

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

♦ Leak through the cylinder head gasket. Check and correct if necessary.

♦ The electric radiator fan does not work.