Engine ZMZ-405, ZMZ-406 does not start

Defect elimination: The crankshaft rotates with the starter, but the engine does not start

First of all, you need to check and troubleshoot problems that are not related to the KMSUD:

• - check the condition of the air filter and clean if necessary;
• - check the correct installation of the camshaft drive (camshaft timing) and, if necessary, install it;
• - check the compression pressure in the engine cylinders (compression) and, if necessary, fix the engine malfunction;
• - check the tightness of the connections of the intake pipe and air ducts with the engine and, if necessary, restore the tightness of the connections.

Next, you need to check the operation of the KMSUD in the mode of displaying fault codes, see the article "Checking the operation of the KMSUD in the mode of displaying fault codes GAZ-3110", and eliminate the identified faults.

Check for sparking

Check for the presence of high voltage using a high-voltage arrester with a spark gap of 4 - 5 mm, connected between the high-voltage wire from the ignition coil and "ground" (Fig. 1).

When the engine is cranked with a starter, sparking should be observed in the arrester.

If there is no sparking, disconnect the wiring harness block from the control unit.

Forcibly turn on the main relay by closing contacts 3 and 19 and, turning on the ignition, check for 12V voltage at terminals 27, 37, 18, 20 and 1 of the block.

If there is no voltage, check the low voltage circuit of the ignition coils (Fig. 2) for an open or broken contact at the wire connections.

If there are no circuit faults, replace the ignition coil or control unit.

Check the condition of the spark plugs 2 (fig. 3) by unscrewing them one by one from the cylinder head.

Spark plugs should not be wet, should not have cracked insulators, damage to the electrodes and large deposits on the electrodes.

The gap between the electrodes of the spark plugs should be between 0.7 and 0.85 mm.

If necessary, dry the candles, clean the electrodes from carbon deposits, set the specified gap between the electrodes of the candles or replace the candles with new ones.

Screw the spark plugs 2 with new O-rings into the cylinder head and put on them the tips 1 of the high voltage wires from the ignition coils in the prescribed order shown in Figure 1.

Check the fuel supply system -

Connect the pressure gauge 6 to the fuel supply line 5 (Fig. 4) using a high pressure hose.

• - Before performing the operation, remove the 15A fuse, thus eliminating the accidental start of the electric fuel pump.
• - When disconnecting fuel hoses, cover the connection point with rags, preventing fuel from spilling and splashing, observe fire safety rules.
• - Install the previously removed 15A fuse and turn on the ignition. In this case, the electric fuel pump should turn on, work for 5 - 7 seconds and then turn off.
• - Check the tightness of the pressure regulator 3.

To do this, remove the vacuum supply hose 4 from the pressure regulator fitting 3, loosening the hose clamp. If there is a leak of gasoline from the fitting, replace the regulator.

- Record the pressure in the system using the manometer.

The pressure in the fuel line must be maintained at 2.6 - 3.0 kg/cm² and not decrease over time.

A lower or higher pressure indicates a system malfunction.

If the pressure is less than the set value, check:

• - the capacity of pipelines and hoses, the absence of contamination, bending, etc.;
• - status of fuel filters.
• - health of the pressure regulator. Replace defective regulator;
• - fuel pump serviceability. Replace the defective fuel pump.

For pressures greater than 3 kg/cm² check:

• - throughput capacity of backflow pipelines and hoses, their absence of contamination, bending, etc.;
• - health of the pressure regulator. Replace defective regulator;

- Check the tightness of the system.

Leaks of gasoline at the junctions of pipelines and hoses 1 - 8 (Fig. 5), as well as at 9 and 10 connections of the injectors with the fuel distributor and the intake pipe are not allowed.

If a gasoline leak is detected, find the cause and repair the leak.

- If necessary, remove the fuel distributor 5 with injectors 2 and pressure regulator 4 from the engine and check the identity of the flow characteristics of injectors 2 and the tightness of pressure regulator 4 on a special stand 3 at a gasoline pressure of 3.0 kg/cm² and temperatures from 15˚ to 20˚С.

Replace the pressure regulator if the test shows:

• - gasoline leak from the regulator discharge fitting;
• - fuel pressure supplied to fuel distributor 5 is not maintained within the specified limits.

Replace injectors with new ones if the following injector malfunctions are detected:

• - sticking of the needle in the open position;
• - the presence of gasoline leakage when the nozzle is closed;
• - underestimated or overestimated in relation to other injectors performance;
• - when 12 V voltage is applied, the nozzle does not work (the click from lifting the sprayer needle is not heard).
• - Install the fuel line on the engine.

If there is no special test bench for injectors, check the tightness of the injector using compressed air.

To check, apply compressed air to the nozzle at a pressure of 2.8 - 3 kg/cm, and dip the spray nozzle into kerosene