Symptoms

Jerks and fading out of ignition in the lower speed range, black smoke when accelerating.
Cause – exhaust gas recirculation

Exhaust gas recirculation valve (EGR valve) it is carbonated or stuck. There may also be a fault in the vacuum control (leakage in the vacuum lines) or in electric control.

Troubleshooting and fault elimination

We conduct a quick test: disconnect the vacuum hose from the EGR valve and test drive. If the vehicle is running "normally", i.e.. no smoking or power drops, use the hand vacuum pump to check the tightness of the air cylinder and air control lines. Opening and closing the valve by means of vacuum is accompanied by a clearly audible "click", the lever must move smoothly, no jams. Must be taken into account, that failure to test the AGR valve may result in saving the fault in the fault memory and activating the emergency operation mode! Another possibility is: connect a U-tube pressure gauge to the control line. A negative pressure must remain in the line up to medium speeds; from approx. 3000 rpm, it should drop evenly, and after fully depressing the accelerator pedal – jump to "zero". This pneumatic control is provided by a solenoid valve clocked by the controller. Should be measured: pulse duty factor, voltage supply (the required value is the battery voltage), condition of electric wires (whether they are not damaged by rodents) and plug connectors, the resistance of the valve winding (Ok. 10-20 Oh). In order to check the condition of the internal components of the EGR valve, it must be removed. If possible, remove any deposits (oil carbon deposits and soot) and check the flue gas side. When reassembling, do not forget to seal carefully.