Let's look at the main faults:
- 1 - when the engine does not start;
- 2 - when engine operation does not meet operational requirements.
To fully diagnose the causes of a malfunction and reduce the time required to find faults, it is necessary to have and immediately include the following equipment in the internal combustion engine control system:
- - diagnostic tester;
- - fuel rail pressure gauge;
- - vacuum gauge;
- - spark gap.
We check whether the engine ECU is controlled, that is, when the ignition is turned on, the diagnostic light comes on and then goes off and the sound of the electric fuel pump is heard.
Therefore, the ECU somehow works to control the engine.
Check the pressure in the fuel line, which should be in the range of 2.5 - 3.0 kg/cm 2 and drop slowly when the fuel pump is turned off.
We turn the crankshaft and use the diagnostic tool in groups to look at the BITSTOP parameter (engine stop sign), which should be present when the crankshaft is turned with the starter.
This indicates that the ECU is receiving a signal from the crankshaft sensor to begin the sparking process.
If there is a spark on the spark plugs, when observed through a high-voltage spark gap, then the ECU completely controls the internal combustion engine, which means that the reason that the internal combustion engine does not start lies, most likely, in the mechanics of the engine. This, as a rule, is either an open circuit or a violation of the valve timing. This is also easy to determine.
In the first case, through the oil filler neck you can see that when the engine is cranked, the camshafts stand still.
In the second case, the violation of the valve timing is checked through compression in the cylinders. Different compression between cylinders mainly indicates this.
1. If the EBN does not work, the reasons may be a malfunction of the pump itself, failure of the EBN turn-on relay, faulty wiring of the control circuit or ESD turn-on, as well as clogged fuel filters.
Immediately disconnect the EBN switching relay and short-circuit the control circuit (for all relays, the contacts on the block are located perpendicularly).
If the EBN is working, then there is a malfunction in the switching relay; if not, then we use a tester to measure the resistance of the EBN with ground, through the same contact.
The absence of resistance indicates that the EBL is broken (the brushes are stuck on the motor armature or the EBL control circuit is faulty).
If the circuit resistance is within 1.5 ohms, then this indicates that the power supply circuit and the EBN winding are working, but the pump will not work for a long time.
It is also possible that the ECU controls the EBN, the EBN works by ear, but there is no fuel pressure.
This is usually a broken or unscrewed fuel intake filter. In any case, you need to look for a malfunction in the fuel supply system. You should always look at the root cause of this:
- - fuel pump noise;
- - jerking of the car;
- - diagnostic light comes on;
- - bouncing of relay contacts.
Rarely, the ECU fails to control the EBN. You can check the serviceability of the circuit using a diagnostic tool by entering the IM control and turning on the EBN relay.
2. If, when cranking the engine crankshaft, the BITSTOP parameter (a sign of engine stop) is present, then most likely the angular synchronization sensor is faulty, or its circuit to the computer is faulty.
The circuit is monitored by the device in the presence of active code 53, and the performance of the sensor is determined by its resistance, which should be in the range of 700-780 Ohms (from experience, a resistance of 620 Ohms is sufficient for the sensor).
3. If there is a signal from the angular synchronization sensor, but there is no spark, then we check the power to the ignition coils (input 15 +12V when the ignition is turned on), as well as the control wires from the short circuit to the computer, the lack of connection with the car body (pins 1 and 20).
If the control wires are connected to the car body (where there is a fault in the electrical wiring) with the short circuit disconnected, this will immediately lead to an explosion of the short circuit.
It’s rare that 2 ignition coils come out at once, but it’s possible.
The ECU also rarely immediately outputs 2 short-circuit control channels consisting of power composite transistors, but more likely than the output of 2 ignition coils.
If there were spare parts, the ECU could be easily repaired.
There are times when everything is fine, but the internal combustion engine does not start.
As a rule, an inexperienced mechanic, seeing that there are no error codes in the ECU, does not pay attention to what temperature the coolant temperature sensor shows.
There is no error code, but the sensor in the ECU provides incorrect information about the temperature of the internal combustion engine, for example 170˚ and the engine practically will not start.
For drivers, you can do this by disconnecting the connector from the coolant temperature sensor and trying to start the engine.
If the internal combustion engine has started, then for further normal operation of the engine Swap the air and liquid temperature sensors, since they are identical in their parameters.
Another reason that the engine does not start may be a failure of the TPS throttle position sensor.
There seem to be no faults through the diagnostic tool, but the THR parameter is more than 80%, and in this case the fuel supply stops.
We do exactly the same as with the coolant temperature sensor. We disconnect the connector from the TPS sensor and the internal combustion engine should start.
But these malfunctions in coolant temperature and TPS are also possible due to the fault of the ECU.
For a complete diagnosis of the CMSUD, you need to have in working order: ECU; EBN; KZ; DPKV.
If the operation of the internal combustion engine does not meet the requirements and has poor driving characteristics, then there are a lot of options and a large field for creative work.
I will focus on the more common options, but each with its own twist, because it is simply impossible to cover everything. So, let's consider the following options:
- - the engine does not develop power;
- - jerks, dips, twitching;
- - unstable operation of the internal combustion engine at idle;
- - the engine accelerates sharply (accelerates);
- - CO is not set.
Let us immediately make a reservation that in all the cases under consideration we will not touch upon the issue of a malfunction of the mechanical part of the engine, but will only consider malfunctions of the internal combustion engine control system, that is, the fuel injection system and the ignition control system.
The engine does not develop power - the reasons for this may be:
- - fuel pressure is below normal;
- - the mass air flow sensor is faulty;
- - air filter is clogged;
- - injectors are coked.
We determine a malfunction of the mass air flow sensor by the DST, by the JAIR parameter of air supply through the mass air flow sensor.
For each type of engine, these readings are different, so you need to approach this issue responsibly.
Even a deviation in air flow, say, by XX of 3-4 kg/hour, leads to significant disturbances in engine operation and therefore it is not necessary for fault codes 13 and 14 to be present.
For example, the idle air flow rate for the 406 engine should be in the range of 13 -15 kg/hour.
If the air flow rate is 10 -11 kg/hour, then the engine will operate unstably, and if the flow rate is 18 - 20 kg/hour, then the duration of the injection pulse, CO, increases accordingly in accordance with the air flow rate, which will lead to higher flow rate fuel.
Coking of injectors occurs due to low-quality fuel.
Injector windings rarely fail electrically.
You can check by turning off the injectors one by one using a diagnostic tool, while checking how much the engine speed drops.
For a normally running engine, the speed should drop by 100-120 rpm. But it still won’t give a clear and visual picture.
Therefore, I would recommend that all car enthusiasts using injection systems clean their injectors at least once a year. This is the most reliable means.
JERKS, DIPS, JERKING - the consequence of this is, as a rule:
- - TPS malfunction;
- - DMRV failures;
- - fuel system malfunction;
- - malfunction of ignition coils and high-voltage wires;
- - ECU malfunction.
TPS malfunction is sometimes very difficult to determine.
This means that when reading from the device through the DST, the opening percentage changes smoothly, and when the throttle valve is opened sharply, sometimes the nonlinearity of the resistance change is not visible, since in some place the resistance path is corroded and as a result the car will twitch.
However, the driver can help determine the malfunction if he provides information that the car jerks at a certain crankshaft speed.
The car behaves similarly when the mass air flow sensor “fails”. When code 13 is present. However, the difference is that the car will jerk at any crankshaft speed.
Failure of ignition coils and high-voltage wires, when a “step” of failure is observed when pressing the gas sharply.
Even checking the ignition coils through an oscilloscope, we will not see the difference in a normally operating coil and one that is malfunctioning.
Therefore, the only reliable method of detection is to replace the ignition coil, with the high-voltage wires in good condition.
Unstable engine idling
- - malfunction of the mass air flow sensor;
- - IAC malfunction;
- - air leak;
- - faulty spark plugs.
If all parameters through the DST are normal, we especially pay attention to the air flow through the mass air flow sensor at idle. We determine air leakage through a vacuum gauge.
I want to dwell on this in more detail, because using a vacuum gauge for engine diagnostics provides very useful information, starting from the condition maintenance of the DBC valves and ending with the serviceability of the exhaust system.
The vacuum gauge is connected directly to the intake manifold. The normal level of vacuum should be 37.5 - 50 mmHg.
When the throttle valve is fully opened, the vacuum should decrease to 0. And when the engine speed decreases, it can increase to 62.5 - 70 mm Hg.
The level of vacuum when rotating the cranked engine with a starter should be 2.5 - 10 mm Hg.
Weak vacuum - intake manifold or throttle gasket, leakage through the vacuum hose, small angle U03. poor camshaft adjustment.
Weak unstable vacuum - intake manifold gasket, injectors.
Regular drop in valve vacuum.
Irregular drop in vacuum - one of the valves, or misfire.
Sharp fluctuations in vacuum and black smoke from the exhaust pipe indicate valve wear.
Weak fluctuation of vacuum - ignition system.
Strong fluctuations in vacuum - weak compression in the cylinders or head gasket.
Slow fluctuation of vacuum - crankcase ventilation system, throttle gasket, fuel mixture composition.
Slow discharge of vacuum after increasing the speed - the condition of the piston rings and the exhaust pipe is clogged.
They can also check the serviceability of the catalyst without unscrewing the lambda probe and without using a back pressure gauge, as indicated in your troubleshooting instructions.
Much simpler and more reliable. If the catalyst is clogged, then when the engine is idling, the vacuum in the intake manifold will gradually decrease.
Then raise the engine speed to 2000 and the vacuum should increase, if not, then the system is clogged.
If, after reducing the speed, the vacuum increases by more than 5 mm Hg, then this also indicates a malfunction of the exhaust system.
If there is no air leak and other elements are in good working order, then this is definitely a violation of the valve timing.
I would also like to highlight the fact that the engine will run unevenly due to bad or non-standard spark plugs.
Now many car enthusiasts use the latest technology. Many people are now advertising pre-chamber candles made in Ukraine.
I would like to immediately warn Volga lovers that they do not run on 406 engines. Use 14 candles and everything will be fine.
I also want to say that the internal combustion engine may stall at idle due to IAC (RDV).
It must maintain the speed at the set level and open and close the additional air supply channel when the speed changes.
But the IAC can raise the speed within 200. And it cannot automatically handle a large drop in speed due to its inertia.
It’s easier to buy an IAC from BOSH, however, its price is the same as the price of an ECU.
It is necessary to maintain the performance of the IAC within its 60 - 90 steps. In this range, it most quickly compensates for the drop in speed, even to the point of raising the throttle a little.
I would also like to note that on 50% of machines the IAC freezes and does not control the XX. There is no need to despair, just remove the engine weight for a while for 2-3 seconds and the IAC will work again.
THE ENGINE IS GAINING - sometimes the engine suddenly starts to rev up suddenly. And you just can’t change your mind.
You check both the fuel system and the +12V power supply system, and change all the sensors, but there is no result. Immediately from practice, because... The device does not detect this is a high voltage failure (plugs, wires, coils).
NO DISPLAY WITH - except for standard faults:
- - TPS is faulty;
- - the mass air flow sensor is faulty;
- - ECU is faulty
There are still interesting options that cannot be determined using a diagnostic tool.
There is a situation where everything seems to be in order, but the CO changes from 0.3% to 5 - 6%; the air is normal, the speed is normal, the position of the TPS sensor is correct, the ignition system is working.
In almost all such cases, I can say that the pressure in the fuel system is higher than normal. Change the pressure relief valve and everything will be fine.
And there are also cases when the CO is small and there is no way to raise it to the required value.
Fuel pressure meets requirements. This means that connect a vacuum gauge and observe, this is usually a faulty pressure relief valve diaphragm.
Tips - how to fool the ECU
The temperature sensor is faulty - either disconnect it or insert a resistance of about 30 Kom into the plug connector;
One of the ignition control channels does not work - open the control unit and resolder one of the transistors of the control circuit.
There is no control of one of the injectors - open the block and connect 2 control circuits for injectors 1 and 4 at the ECU plug connector, or 2 and 3 depending on which injector does not work;
The lambda probe does not work (from practice), changing the supply voltage to it through a regular resistance, bringing the output voltage to 0.4 V, usually helps.