Possible engine malfunctions, their causes and methods of elimination

Engine won't start

Cause of malfunction	Elimination Method
1. No fuel in carburetor:	1. Do the following:
- clogged fuel lines or fuel filter;	- blow out the fuel lines, flush the fuel tank, replace the fuel filter;
- clogged carburetor and fuel pump filters;	- wash the filters;
- the fuel pump is faulty.	- Check pump operation and replace damaged parts.
2. Faulty ignition system,	2. See subsection «Ignition system».
3. The carburetor solenoid valve does not open when the ignition is turned on:	3. Do the following:
- a break in the wires going to the valve control unit and to the valve;	- check wires and their connections, replace damaged wires;
- the solenoid valve control unit is faulty;	- replace the control unit;
- Faulty solenoid valve.	- replace the valve.
4. The carburetor choke does not open at the first flashes in the cylinders.	4. Repair leaks in carburetor starter.

Engine runs erratically or stalls at idle

Cause of malfunction	Elimination Method
1. Engine idle adjustment is broken.	1. Adjust idling.
2. Faulty carburetor solenoid valve control system.	2. See fault «Engine won't start».
3. Faulty carburetor:	3. Do the following:
- jets or carburetor channels are clogged;	- blow jets and carburetor channels;
- water in the carburetor;	- remove water from the carburetor, drain sediment from the fuel tank;
- the tightness of the diaphragm of the starting device is broken.	- replace diaphragm.
4. Faulty ignition system.	4. See subsection «Ignition system».
5. Air leak through a damaged hose connecting the intake pipe to the vacuum brake booster.	5. Replace damaged hose.
6. Air leakage through gaskets in the intake pipe connections to the carburetor or cylinder head.	6. Tighten the fastening nuts or replace the gaskets; repair the deformation of the carburetor flange or replace the carburetor.
7. Air leakage through a damaged vacuum sampling tube to the ignition distribution sensor.	7. Replace damaged tube.

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

Cause of malfunction	Elimination Method
1. Incomplete opening of the throttle valves of the carburetor.	1. Adjust the throttle actuator.
2. The air filter element is dirty.	2. Replace filter element.
3. Faulty ignition system.	3. See subsection «Ignition system».
4. Faulty fuel pump.	4. Check pump operation and replace damaged parts.
5. Faulty carburetor:	5. Do the following:
- the accelerator pump is faulty;	- check pump flow, replace damaged parts;
- clogged main jets;	- blow jets with compressed air;
- the air damper is not fully open;	- adjust the air damper drive;
- the fuel level in the float chamber does not correspond to the norm;	- adjust the float setting;
- the tightness of the diaphragm of the economizer of power modes is broken.	- replace diaphragm.
6. Clogged fuel tank vent tube.	6. Blow out the tube with compressed air.
7. Clearances in the valve mechanism are broken.	7. Adjust gaps.
8. The timing marks of the valve timing do not match.	8. Rearrange the chain, aligning the alignment marks.
9. Insufficient compression below 1MPa (10 kgf/cm2):	9. Do the following:
- breakage or occurrence of piston rings;	- clean the rings and grooves of the pistons from deposits, replace the damaged parts;
- poor fit of valves to the seats;	- replace damaged valves, grind seats;
- Excessive wear of cylinders and piston rings.	- replace pistons, bore and honing cylinders.

Knocking crankshaft bearings

Usually a dull tone, metallic. It is detected when the throttle valves are suddenly opened at idle. Its frequency increases with an increase in the frequency of rotation of the crankshaft. Excessive axial clearance of the crankshaft causes a sharper knock with uneven intervals, especially noticeable with a smooth increase and decrease in the crankshaft speed.

Cause of malfunction	Elimination Method
1. Too early ignition.	1. Adjust ignition timing.
2. Insufficient oil pressure.	2. See fault «Insufficient oil pressure at idle».
3. Loose flywheel bolts.	3. Tighten the bolts to the recommended torque.
4. Increased clearance between the journals and the main bearing shells.	4. Sand the necks and replace the liners.
5. Increased clearance between thrust washers and crankshaft.	5. Replace thrust washers with new ones, check clearance.

Knocking rod bearings

Usually the knock of the connecting rod bearings is sharper than the knock of the main bearings. It is heard at idle speed of the engine with a sharp opening of the throttle valves. The place of knocking is easy to determine by turning off the spark plugs in turn.

Cause of malfunction	Elimination Method
1. Insufficient oil pressure.	1. See fault «Insufficient oil pressure at idle».
2. Excessive clearance between crankshaft journals and bearings.	2. Replace liners and grind necks.

The knock of pistons

The knock is usually unvoiced, muffled; called «beating» piston in the cylinder. It is best heard at low engine speeds and under load.

Cause of malfunction	Elimination Method
1. Increased clearance between pistons and cylinders.	1. Replace pistons, bore and honing cylinders.
2. Excessive clearance between piston rings and grooves on the piston.	2. Replace rings or pistons with rings.

Knocking inlet and outlet valves

Increased clearances in the valve train cause a characteristic knock, usually at regular intervals; its frequency is less than the frequency of any other knock in the engine, since the valves are driven by the camshaft; the rotational speed of which is two times less than the rotational speed of the crankshaft.

Cause of malfunction	Elimination Method
1. Increased clearances in the valve mechanism.	1. Adjust clearances.
2. Broken valve spring.	2. Replace spring.
3. Excessive clearance between valve and guide sleeve.	3. Replace worn parts.
4. Wear of the camshaft cams.	4. Replace the camshaft and valve levers.
5. Unscrewing the locknut of the adjusting bolt.	5. Adjust the gap between the lever and the camshaft cam, tighten the locknut.

Excessive Camshaft Drive Circuit Noise

From the general noise of the engine, the noise of the camshaft drive circuit stands out when gaps appear between the gearing elements and is clearly audible at a low crankshaft speed.

Cause of malfunction	Elimination Method
1. The chain is loose due to wear.	1. Tension the chain.
2. Breakage of the shoe of the chain tensioner or damper.	2. Replace tensioner shoe or damper.
3. Jamming of the plunger rod of the chain tensioner.	3. Remove the jam.

Insufficient oil pressure at idle with a warm engine

Cause of malfunction	Elimination Method
1. Foreign particles under the pressure reducing valve of the oil pump.	1. Clean the valve from foreign particles and burrs, flush the oil pump.
2. Stuck pressure reducing valve.	2. Replace valve.
3. Worn oil pump gears.	3. Repair the oil pump.
4. Excessive clearance between bearings and crankshaft main journals.	4. Sand the necks and replace the liners.
5. Excessive clearance between journals and camshaft bearing housings.	5. Replace camshaft or bearing housing.
6. The use of engine oil of an inappropriate brand and quality.	6. Change the oil to another one recommended in Annex 4.

Excessive oil pressure on a warm engine

Cause of malfunction	Elimination Method
1. Stuck oil pressure reducing valve.	1. Replace valve.
2. The spring of the oil pressure reducing valve is more rigid.	2. Replace spring.

Increased oil consumption

Cause of malfunction	Elimination Method
1. Oil leakage through engine seals.	1. Tighten fasteners or replace gaskets and seals.
2. Clogged crankcase ventilation system.	2. Wash the parts of the crankcase ventilation system.
3. Wear of piston rings or engine cylinders.	3. Rebore cylinders and replace pistons and rings.
4. Breakage of piston rings.	4. Replace rings.
5. Coking of slots in oil scraper rings or grooves in piston grooves due to the use of non-recommended oil.	5. Clean the slots and grooves from carbon deposits, replace the engine oil with the recommended Annex 4.
6. Wear or damage to valve stem seals.	6. Replace oil seals.
7. Increased wear on valve stems or guide bushings.	7. Replace valves, repair cylinder head.

Increased fuel consumption

Cause of malfunction	Elimination Method
1. Carburetor choke not fully open.	1. Adjust the air damper actuator.
2. Increased resistance to vehicle movement.	2. Check and adjust tire pressure, brake system, wheel alignment.
3. Incorrect ignition timing.	3. Adjust ignition timing setting.
4. The vacuum regulator of the ignition distributor is faulty.	4. Replace the vacuum regulator or ignition distributor.
5. High fuel level in the carburetor:	5. Do the following:
- the tightness of the needle valve or its gasket is broken;	- check that there are no foreign particles between the needle and the valve seat, if necessary, replace the valve or gasket;
- sticking or increased friction, preventing the normal movement of the floats.	- check and, if necessary, replace the floats.
6. Clogged carburetor air jets.	6. Clean the jets.
7. The tightness of the diaphragm of the economizer of the power modes of the carburetor is broken.	7. Replace diaphragm.
8. The carburetor solenoid valve does not shut off the fuel supply at forced idle:	8. Do the following:
- does not close with «weight» movable contact of the limit switch;	- clean the contact surfaces of the switch;
- a break in the wire connecting the control unit to the carburetor limit switch;	- check its connections; replace the damaged wire;
- Faulty control unit.	- replace the control unit.

Engine overheating

The pointer of the coolant temperature gauge is in the red zone of the scale. Before troubleshooting, make sure that the coolant temperature gauge and its sensor are working (see subsection «control devices»).

Cause of malfunction	Elimination Method
1. The pump and alternator drive belt is loose.	1. Adjust belt tension.
2. Insufficient amount of fluid in the cooling system.	2. Add coolant to the cooling system.
3. Incorrect ignition timing.	3. Adjust the setting. moment of ignition.
4. The outer surface of the radiator is heavily soiled.	4. Clean the outer surface of the radiator with a jet of water.
5. Faulty thermostat.	5. Replace thermostat.
6. Faulty radiator plug valve (opening pressure less than 0.07 MPa (0.7 kgf/cm2).	6. Replace plug.
7. Faulty coolant pump.	7. Check pump operation, replace or repair.

Rapid drop in fluid level in expansion tank

Cause of malfunction	Elimination Method
1. Damaged radiator.	1. Repair or replace the radiator.
2. Damage to hoses or gaskets in pipeline connections, loosening of clamps.	2. Replace damaged hoses or gaskets, tighten hose clamps.
3. Fluid leakage from a tap or heater radiator.	3. Replace faucet or radiator.
4. Fluid leakage through the coolant pump seal.	4. Replace the oil seal.
5. Damaged radiator cap or gasket.	5. Replace plug.
6. Damaged cylinder head gasket.	6. Replace gasket.
7. Fluid leakage through microcracks in the block or in the cylinder head.	7. Check up tightness of the block and a head of cylinders, at detection of cracks replace the damaged details.
8. Liquid leakage through microcracks in the coolant pump housing, in the outlet pipe of the cooling jacket, in the thermostat, expansion tank or inlet pipe.	8. Check the tightness, if cracks are found, replace the damaged parts; an insignificant leak can be eliminated by adding a sealant of the NIISS-1 type to the coolant.