The situation when the engine ZMZ-406 with distributed fuel injection, it refuses to start the first time, familiar to many owners of GAZelle and Volga cars. Instead of a confident start, the driver hears long seconds of starter operation, the “sneezing” of the engine, or complete silence, despite a working battery. Often the problem lies not in one specific node, but in a combination of factors related to the age of the control system Mikas 5.4 or Mikas 7.1.
For successful diagnostics, it is necessary to understand the physics of the process: to ignite the mixture, you need a spark of the required power, fuel at a certain pressure and correct readings from the crankshaft position sensors. If at least one of these parameters is outside the tolerance limits, ECU (electronic control unit) does not give the start command or supplies the mixture too lean. In this article we will analyze in detail the main causes of difficult starting and methods for eliminating them.
The first thing you should pay attention to is the nature of the difficult start-up. The engine may have difficulty starting “cold” when the car has been parked overnight, or “hot” after a short stop. These symptoms indicate completely different malfunctions in the fuel supply and ignition systems. Ignoring the primary symptoms often leads to the fact that the car completely stops starting at the most inopportune moment.
Diagnostics of the fuel supply and pressure system
The most common reason why ZMZ-406 The starter turns for a long time, which is caused by a drop in pressure in the fuel rail after stopping the engine. In a working system, fuel should remain in the rail for a long time thanks to a check valve in the fuel pump or pressure regulator. If the valve does not hold, gasoline flows back into the tank, and the pump takes time to re-inflate the line when the ignition is turned on.
The pressure should be checked using a pressure gauge connected to the fuel rail. A normal indicator for an injection 406 engine is considered to be a pressure in the range 2.8–3.0 atmospheres at idle speed. If the pressure gauge needle drops immediately after the ignition is turned off, it means that the tightness of the system is broken. This may be caused by wear of the fuel pump itself, which is located in the tank, or leaking injectors.
⚠️ Attention: Before disconnecting the fuel hoses, be sure to relieve pressure in the system by removing the fuel pump fuse and letting the engine run until it stops. Attempting depressurization may result in fire or personal injury.
It is also worth checking the condition of the fine fuel filter. A clogged filter creates resistance that the pump cannot overcome, especially under load or when attempting a quick start. Owners often forget to change this consumable, which leads to a gradual deterioration in dynamics and problems with starting.
Replace the fuel filter along with the fuel pump mesh - this is a basic maintenance procedure that solves 30% of starting problems.
To quickly assess the state of the system, you can use the following algorithm of actions:
- 🔧 Turn on the ignition without starting the starter and listen to the hum of the pump in the tank.
- 🔧 Repeat turning on the ignition 2-3 times with an interval of 5 seconds to increase the pressure.
- 🔧 If the engine starts easily after turning it on multiple times, the problem is a pressure drop (check valve).
- 🔧 Check if the fuel hoses are pinched and if there is a characteristic smell of gasoline under the bottom.
Malfunctions of sensors and electronic control unit
The injection engine is completely dependent on sensor readings. If ECU receives incorrect data, it cannot calculate the correct duration of opening of the injectors. The critical element here is DPKV (crankshaft position sensor). It is he who tells the “brains” of the car what position the pistons are in and when a spark needs to be supplied.
If the DPKV malfunctions, the engine most often does not start at all, but there are times when there is a signal, but it is weak or intermittent due to contamination or damage to the wiring. The gap between the end of the sensor and the crankshaft toothed pulley should be 0.5–1.5 mm. Too much clearance will cause the signal to disappear at high speeds or during startup.
The second important element is Mass air flow sensor (mass air flow sensor). If it malfunctions, the mixture may be either too rich or too lean. If the sensor “lies” towards a lean mixture, the engine will have difficulty starting when cold, stall at idle and jerk during acceleration. Temporarily disabling the mass flow sensor chip often helps: if the engine runs more smoothly (even with increased flow), the sensor requires replacement.
| Sensor | Problem Symptom | Test method |
|---|---|---|
| DPKV | No spark, no start | Resistance measurement, gap check |
| Mass air flow sensor | Unstable XX, bad start | Disabling the chip, measuring voltage |
| DTOZH | Cold starting problems | Resistance measurement at different temperatures |
| RXX | Stalls when releasing gas | Cleaning the channel, checking the stroke of the rod |
Third on the list, but not least important - DTOZH (coolant temperature sensor). If it shows the ECU that the engine is hot when in fact it is cold, the control unit will not give the command to enrich the mixture for starting. As a result, the spark plugs flood and the engine does not engage.
Problems with the ignition system and spark plugs
Ignition system ZMZ-406 Structurally, there are two types: with a distributor (earlier versions) and without a distributor (SOATE or Mikas-7.1 with two two-terminal coils). In both cases, weak sparking is a common cause of long startup times. Soot on spark plugs, breakdown of high-voltage wires or cracks in the ignition coil do not produce a powerful spark necessary to ignite the mixture.
Inspect the spark plugs. If they are black and wet with gasoline, the mixture is too rich or the spark is too weak. If the candles are white or have a reddish coating, the mixture is poor. The normal color of the electrode is light brown. The gap on the spark plugs for the injection 406 must be strictly 0.7–0.85 mm. A larger gap requires more voltage to break down, which an older coil may not be able to provide.
⚠️ Attention: When checking the spark “to ground”, do not hold the wire or coil in your hands. Use dielectric pliers to avoid electric shock; the voltage in the ignition system reaches 25,000 Volts.
Pay special attention to the commutator and coil. On older GAZ cars, these elements often overheat. If after a long period of inactivity the car starts up poorly, but after warming up the problem disappears, a breakdown probably occurs inside the coil when heating up. It is also worth checking the integrity of the armored wires: in the dark, with the hood open, you can see “northern lights” (sparks) on the surface of the wires, which indicates a current leak.
For owners of cars with a distributor, it is important to check the runner and distributor cap. Oxidized contacts inside the cover create high resistance, weakening the spark. The distributor slider and cover should be replaced every 30-40 thousand kilometers, since the graphite contact of the slider is erased and the gap increases.
Effect of idle air control and throttle valve
Idle speed control (RXX) is responsible for supplying air bypassing the closed throttle valve. When the engine starts, the ECU opens the IAC by a certain step to provide the required volume of air. If the regulator rod is coked with carbon deposits or jammed, not enough air is supplied and the engine “chokes” without developing the required speed to start.
Cleaning the throttle body is a procedure that is often ignored. Oily deposits from the crankcase ventilation system accumulate on the walls of the damper and in the IAC channel. This deposit blocks the channel cross-section, and even a fully extended IAC rod cannot pass the required amount of air. For cleaning, use special aerosols for carburetors and a soft brush.
☑️ Cleaning the throttle body
After cleaning the IAC and throttle, an adaptation procedure is often required. To do this, on some firmware versions you need to reset the battery terminal for 10-15 minutes so that the ECU forgets the old parameters. After connecting the terminal, turn on the ignition for 10 seconds (without starting the engine), then turn off. Repeat 3 times, then start the engine and let it idle for 5-7 minutes without pressing the gas.
Features of starting on a hot and cold engine
The nature of the difficult start gives the key to understanding the problem. If ZMZ-406 It doesn’t start well “in the cold” when the car has been parked overnight, most likely it’s due to a drop in fuel pressure or a malfunction of the DTO. The engine does not have enough rich mixture, and the starter has to turn the crankshaft for a long time until the pump pumps up the ramp or the spark plugs dry out.
The situation when the engine starts perfectly cold, but stalls or does not start after a short stop (10-20 minutes) in the heat, is called “vapor lock” or overheating of the elements. In this case, gasoline boils in the ramp, forming gas plugs that interfere with the supply of liquid fuel. Also, when hot, the DPKV signal may be lost due to heating of the winding.
To combat hot starting, experienced drivers use the “blow-through” method. If the engine does not start, press the gas pedal all the way (full load mode) and turn the starter for 3-5 seconds. In this mode, the ECU shuts off the injectors and blows air through the cylinders, removing excess gasoline. After this, release the gas and try to start the engine as usual.
Why do the spark plugs flood on a 406 engine?
Spark plug flooding occurs when too much fuel enters the cylinders and does not have time to burn. The main reasons: weak spark, faulty mass air flow sensor (shows a lot of air), jammed IAC or low compression. Also, the spark plugs flood during frequent attempts to start without drying the cylinders.
Mechanical problems and compression
The mechanical condition of the engine should not be discounted. ZMZ-406 known for its sensitivity to the condition of the timing chain. A stretched chain disrupts the valve timing, causing the valves to open at the wrong time. This leads to a drop in compression and difficult starting, especially at low starter speeds.
Checking compression is a mandatory step in deep diagnostics. The normal value for the 406th motor is 10–12 atmospheres. If the pressure in one of the cylinders is significantly lower (dispersion of more than 1 atm), the engine will stall and have difficulty starting. Low compression can be caused by worn piston rings, burnt-out valves, or a blown cylinder head gasket.
It is also worth mentioning the suction of unaccounted air. Cracks in the intake manifold (especially true for plastic manifolds on newer versions), pipes or injector O-rings lead to a lean mixture. The ECU tries to compensate for this by increasing the injection time, but at idle and during startup this is not always possible.
If the compression is normal, the fuel pressure is maintained, the spark is powerful, but the engine does not start - check the timing marks. Missed phases are a common hidden cause of problems on run-on ZMZ engines.
Frequently asked questions (FAQ)
Why does the ZMZ 406 start only with the gas pedal pressed?
This is a classic sign of a malfunctioning idle air control (IAC) or a strong air leak. When you open the throttle, air enters directly, bypassing the coked IAC channel, and the mixture becomes flammable. This may also indicate that the ECU does not see the closed position of the throttle valve (TSP malfunction).
What gasoline is better to pour into a fuel-injected 406 engine?
The plant recommends using AI-92 gasoline. However, due to the engine's tendency to detonate when the ignition is incorrectly set or carbon deposits, many owners switch to AI-95. This may improve performance at high rpm, but will not solve starting problems if the problem is in the sensors.
How to reset Mikas ECU errors without a scanner?
The easiest way is to remove the negative terminal from the battery for 15-20 minutes. This will reset the ECU's RAM. However, if the cause of the malfunction is not eliminated, the error will appear again after several engine operation cycles. You can also remove the ECU power fuse (usually 5A) with the ignition off.
Is it possible to drive if the car starts only the second time?
You can drive, but it is not advisable. Constant underheating of the spark plugs during long starting attempts leads to their contamination and failure of the catalytic converter (if there is one). In addition, frequent “oil drainage” during unsuccessful starts increases oil consumption and wear of the piston group.