Possible malfunctions of ZMZ-402 and ZMZ-4021

If you think that sounds have appeared during engine operation that were not there before, immediately check if everything is in order with the engine

Most often, knocking in the engine is associated with serious malfunctions, for the diagnosis and elimination of which it will be necessary to disassemble the engine in a service center or garage.

You can try to independently determine the cause of the knocking in order to decide whether to go to the car service on your own or by tow.

Cause of the malfunction (Remedy)

The engine does not start

Lean combustible mixture (pops in the carburetor):

  • - the mesh is clogged carburetor filter, fuel pump filter or fine fuel filter - Wash the filter in unleaded gasoline and blow it out with compressed air
  • - the diaphragm is torn or the seal of the fuel pump valves is broken - Replace the diaphragm or valves
  • - the water in the sump or fuel line is frozen - Warm up the sump or fuel line with hot water
  • - the fuel line is clogged - Blow out the fuel line
  • - the carburetor air damper does not close completely; - Adjust the choke drive
  • - the jet is clogged: main fuel and idle - Wash in unleaded gasoline and blow out the jets with compressed air
  • - the carburetor is loosened to the intake pipe or the intake pipe to the cylinder head - Tighten the fasteners, replace the gaskets if necessary
  • - low fuel level in the carburetor float chamber - Adjust the fuel level
  • - the exhaust gas recirculation valve is stuck in the open position - Replace the recirculation valve

Rich combustible mixture (pops in the muffler when starting the engine):

  • – the carburetor air damper does not open completely - Adjust the choke drive dampers
  • – fuel supply valve is not tight - Replace the valve sealing washer
  • – float is not tight - Restore float tightness or replace the float
  • – air jets of the metering systems are clogged - Flush the jets with unleaded gasoline and blow with compressed air
  • – mixture quality screw is not adjusted correctly - Adjust the required mixture composition
  • – fuel level in the carburetor float chamber is too high - Adjust the fuel level

The engine does not start in cold weather:

  • - Air damper does not close - Adjust the air damper drive

The engine runs unsteadily in idle mode stroke:

  • - High or low fuel level in the carburetor float chamber - Adjust the fuel level
  • - Incorrectly adjusted idle speed - Adjust the required mixture composition
  • - Large amount of water in the sump of the fine fuel filter and fuel tank - Drain the sediment from the filter and tank
  • - Incorrect adjustment of the valve clearances - Adjust the valve clearances
  • - Loose fastening of the carburetor, intake pipe, gas line - Tighten the fastenings, replace the gaskets if necessary

Increased toxicity of exhaust gases:

The engine does not develop full power and does not have sufficient throttle response:

  • - Carburetor accelerator pump is faulty - Check pump feed, replace damaged parts
  • - Low fuel level in carburetor float chamber - Adjust fuel level
  • - Valve clearances are out of adjustment - Adjust valve clearances
  • - Carburetor throttle valves do not open fully - Adjust throttle valve drive
  • - Lean fuel mixture - See «Engine does not start (lean fuel mixture) mixture)»
  • - The air filter element is clogged - Replace the filter element
  • - The valve drive clearances are out of adjustment - Adjust the valve drive clearances
  • - The Winter-Summer flaps position does not correspond to the season - Set the flaps to the position corresponding to the season

Increased fuel consumption:

  • - Lean or rich combustible mixture - See «The engine does not start»
  • - The air filter element is clogged - Replace the filter element
  • - Incorrect setting of the initial ignition timing - Adjust the initial ignition timing
  • - The vacuum corrector of the ignition distributor is faulty - Replace vacuum corrector or distributor
  • - The tightness of the power supply system is broken ia - Restore tightness
  • - Increased resistance to vehicle movement - Check and adjust the brake system, wheel bearings, air pressure in the tires

Engine overheating:

  • - Thermostat is faulty - Replace the thermostat
  • - Weak tension of the fan and water pump drive belts - Adjust the belt tension
  • - Incorrect setting of the initial ignition timing - Adjust the initial ignition timing
  • - Lean combustible mixture - See "The engine does not start (lean combustible mixture)"
  • - Severe contamination of the radiator - Flush the cooling system, flush the radiator with a stream of water
  • - Increased resistance to vehicle movement - Check and adjust the brake system, wheel bearings, air pressure in the tires
  • - Faulty water pump - Replace the pump
  • - Engine continues to run after the ignition is turned off - Engine overheating See "Engine overheating"
  • - Low-octane fuel used - Use fuel with the appropriate octane rating

Detonation knocks in the engine:

  • - Early setting of the initial ignition timing - Adjust the initial ignition timing
  • - Large layer of carbon deposits on the walls of the combustion chambers and piston crowns - Clean the carbon deposits
  • - Low-octane fuel used - Use fuel with the appropriate octane rating

Insufficient oil pressure when warmed up engine:

  • - Malfunction or clogging of the oil pressure relief valve - Flush the valve parts and the seat in the oil pump housing, replace the spring or valve if necessary
  • - Faulty oil pressure sensor or indicator - Check the pressure with a control pressure gauge, replace the faulty device
  • - Engine overheating - Turn on the oil radiator, eliminate the cause of overheating
  • - Excessive wear of the main bearing shells - Replace the shells
  • - Wear of the oil pump parts - Replace the gasket between the housing and the cover with a thin paper gasket or replace the pump

Increased oil consumption:

  • - Excessive wear of the piston rings - Replace the piston rings
  • - Clogged crankcase ventilation system - Flush unleaded gasoline and blow out the hoses and ventilation channels in the intake pipe and the oil separator parts in the rocker cover with compressed air
  • - Oil leak through engine seals - Tighten the connections, replace the gaskets or seals if necessary
  • - Excessive wear or destruction of the valve stem seals - Replace the seals

Knocks in the engine:

  • - Wear of the connecting rod and piston group - Repair the engine
  • - Large clearances between the rocker arms and valves - Adjust the clearances in the valve drive
  • - Large clearances between the valve stems and guide bushings - Replace worn parts or the head with valves as an assembly
  • - Wear of the camshaft cams and tappets - Replace worn parts
  • - Large gap between thrust rings and crankshaft - Replace thrust rings