Main faults of the power supply system (VAZ-2109)

The engine does not start when cold

The starter turns the crankshaft, but the engine does not start.

Causes of malfunction and methods of elimination:

• no fuel is supplied to the carburetor. It is necessary to disconnect the hose from the discharge pipe of the fuel pump and check the fuel supply using the manual pumping lever. If fuel is not supplied, disconnect the hose from the suction pipe and check whether a vacuum is created at the inlet of this pipe. If there is no vacuum, check the fuel pump by removing the cover and the upper housing of the pump, flush the fuel filter and make sure the diaphragms are intact. If there is a vacuum at the inlet of the suction pipe, the cause of the malfunction should be sought in the fuel lines, fuel tank or fine fuel filter. It is necessary to blow out the fuel lines with a tire inflation pump. In this case, gurgling sounds should be heard in the fuel tank. The fine filter may be clogged. It is necessary to remove it from the hoses, connect the hoses and start the engine. Check for changes in engine operation with the filter removed. If necessary, replace the filter with a new one. After removing the fuel tank, flush it with gasoline. To remove the tank, disconnect the ground wire from the battery, lift the rear seat cushion and remove the hatch cover located on the floor under the mat. Disconnect the electrical wires and hoses from sensor 9 (see figure 39) fuel level. Remove as much fuel as possible from the tank. Loosen clamps 17 securing the fuel tank, disconnect hoses 15 and 13 and remove the tank. Drain any remaining fuel from the tank. Install the tank in the reverse order;
• the electromagnetic shut-off valve of the carburetor does not open when the ignition is turned on due to a break in the wires going to the valve control unit and to the valve, as well as due to malfunctions of the valve control unit or the valve itself. It is necessary to check the condition of the wires and their connections. Replace damaged wires. If the electromagnetic valve or control unit is faulty, replace them with new ones;
• the ignition system does not work. The method of checking and troubleshooting is described in the chapter "Ignition system";
• the air damper does not open at the first flashes in the cylinders. Turning the crankshaft with the starter, check whether the air damper lever turns with the carburetor starting device rod at the first flashes in the cylinders. If not, you need to disassemble the starting device and check the tightness of its diaphragm, eliminate the jamming of the rod;
• the air damper does not close. Check the air damper drive, adjust the length of the rod so that when the handle is pulled, the air damper is completely closed.

Engine runs rough or stalls at idle

The malfunction is determined by an uneven exhaust sound and sudden engine stops at idle.

The text is copied from the online portal vazbook

Causes of the malfunction and ways to eliminate it:

• the ignition system is not working satisfactorily. The method of checking and troubleshooting is described in the chapter "Ignition system";
• the carburetor idle speed adjustment is out of adjustment. Adjust the engine idle speed;
• malfunctions in the carburetor forced idle economizer system. Check the operability of the forced idle economizer;
• the jets and channels of the carburetor idle system are clogged. Disassemble the carburetor, wash it with gasoline and blow out the channels and jets with compressed air;
• water entering the carburetor. Remove water from the carburetor and fuel tank;
• air is being sucked in through a damaged diaphragm in the starting device. Replace the diaphragm;
• air is being sucked in through the hose going to the brake booster or through the hose to the vacuum ignition timing regulator. Check the hoses and the reliability of their fastening to the pipes, tighten the clamps if necessary. If the hose is damaged, you can temporarily fix its leak with adhesive tape and replace the hose as soon as possible;
• air leaks through gaskets in the connections of the intake manifold to the carburetor or cylinder head. Tighten the carburetor mounting nuts (only on cold engine) and intake manifold. Replace gaskets if necessary;
• air is being sucked in through a damaged vacuum sampling tube to the economizer. Replace the damaged tube.

The engine runs unevenly and unstably at high crankshaft speeds

Causes of the malfunction and ways to eliminate it:

• malfunctions in the ignition system. Check and correct as indicated in the chapter "Ignition system";
• the jets of the main metering system of the carburetor are clogged. Disassemble the carburetor, wash it with gasoline and blow out its jets and channels with compressed air.

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

Causes of the malfunction and ways to eliminate it:

• incomplete opening of the carburetor throttle valves. Adjust the throttle valve drive;
• air filter contamination. Replace filter element;
• the ignition system is faulty. Check and fix as described in the chapter "Ignition system";
• the fuel pump is faulty. Check the pump operation, replace damaged parts if necessary;
• the accelerator pump does not work. Check the performance of the accelerator pump and the condition of the pump parts, replace damaged parts if necessary;
• the main fuel jets are clogged. Disassemble the carburetor, wash it in gasoline and blow it out with compressed air;
• the air damper is not fully open. Check and adjust the carburetor air damper drive;
• the fuel level in the carburetor float chamber is not correct. Remove the carburetor and adjust the fuel level in the float chamber;
• the tightness of the diaphragm of the power mode economizer is broken. Remove the diaphragm, check its condition, if damaged, replace the diaphragm;
• detonation in engine cylinders due to the formation of a significant layer of carbon deposits on the piston crown and combustion chamber walls. It is recommended to contact a service station to remove the engine cylinder head and clean the combustion chambers, pistons and valves from carbon deposits;
• clogging of the tube or check valve of the gasoline vapor separator. Blow out the tube with the valve with compressed air;
• clearances in the valve mechanism are damaged. Check and fix as indicated in the chapter "Gas distribution mechanism";
• insufficient compression in the engine cylinders. Check and correct as indicated in the chapter "Crank mechanism".

Engine misfires in all modes

Causes and ways to eliminate them:

• the ignition system is faulty. The testing and troubleshooting methods are described in the chapter "Ignition system";
• presence of water at the bottom of the fuel tank. Remove sediment from the fuel tank. If necessary, remove the tank and wash it with gasoline;
• the fuel lines or filters of the carburetor, fuel pump or fine fuel filter are clogged. Blow out the fuel lines with a tire pump, remove the filters and wash them in gasoline;
• the jets and channels of the carburetor are clogged. Disassemble the carburetor and wash its jets and channels with gasoline, blow out with compressed air;
• increased or decreased fuel level in the carburetor float chamber. When the fuel level in the carburetor is increased, the combustible mixture is over-enriched, which is characterized by black exhaust, "shots" in the muffler. When the level is decreased, the mixture is depleted, which is manifested by pops in the intake manifold. Disassemble the carburetor and adjust the fuel level in the float chamber;
• the adjustment of the gaps in the valve timing mechanism is disturbed. Check and adjust the gaps (see chapter "Gas distribution mechanism").

Increased fuel consumption

Fuel consumption depends largely on driving style, season, and vehicle operating conditions (driving in the city, on highways for long distances or on country roads). Therefore, it is difficult to name a specific fuel consumption figure. Normal fuel consumption per 100 km, measured using a special method, with a four-speed gearbox (five-speed) should be no more than 8.6 l (8.6 l) when used in the city, 6.1 l (5.7 l) on the highway at a speed of 90 km/h and 8.2 l (7.8 l) at a speed of 120 km/h.

However, if under the same operating conditions of the vehicle, fuel consumption has increased, the causes of the malfunction and methods of elimination are as follows:

• the carburetor air damper does not open fully. Check and adjust the air damper drive;
• increased resistance to vehicle movement due to incorrect tire pressure, wheel alignment angles, or incomplete release of the wheels. Check and adjust tire pressure and wheel alignment angles. Troubleshoot the brake system as described in Chapter "Brake system";
• incorrect ignition timing. Check and adjust ignition timing;
• high fuel level in the carburetor float chamber. Remove and disassemble the carburetor, check and adjust the carburetor float setting;
• the air jets of the main metering systems of the carburetor are clogged. Disassemble the carburetor, wash the jets and channels with gasoline and blow out with compressed air;
• the vacuum regulator of the ignition distributor sensor does not work. Contact a service station to have the vacuum regulator checked on a bench and adjusted or replaced;
• the tightness of the diaphragm of the carburetor power economizer is broken. Remove the diaphragm, check its condition, replace it with a new one if necessary;
• the carburetor power mode economizer spring has weakened. Replace the spring with a new one;
• the electromagnetic shut-off valve of the carburetor does not shut off the fuel supply at forced idle speed due to the failure of the carburetor limit switch to close, or a break in the wire connecting the control unit to the carburetor limit switch, or a malfunction of the electronic control unit. Clean the contact surfaces of the switch, check the condition of the wires. Replace the faulty control unit with a new one;
• insufficient compression in the engine cylinders. Fix as described in the chapter "Crank mechanism".