Symptoms

In the customer's car, there are short-term decays of auto-ignition while driving in all speed ranges, similar to misfiring in a positive-ignition engine (this applies especially to earlier engines produced up to approx. 1995 r., when design changes are made to the sprayer needle lift sensor).

Cause – the sprayer needle lift sensor is not working properly

The spray needle lift sensor sends signals to the engine control unit, which are considered unreliable. For this reason, the controller "detects" the allegedly overspeed and stops fuel injection for a short time (for engine protection).

Troubleshooting and fault elimination

First read the fault memory. Fault code records, indicating that the signals of the sprayer needle lift sensor are unreliable, should be interpreted as damage to this sensor. In practice, however, it turns out, that often none of the above-mentioned. faults!

In this case, the sprayer needle lift sensor should be checked: start the engine and idle speed up, to say the least 4000 rpm. Then tap with the screwdriver handle or similar tool (do not hit!) in the injector with the nozzle lift sensor (it is generally the third cylinder). If the engine stops or runs rough, means, that the sensor is broken. The EDC controller recognizes knocking as excessive revolutions and drastically reduces the size of the injected fuel doses. This manual "fault generation" may also not be saved in the fault memory.

As you know, the task of the sprayer needle lift sensor is to inform the controller about the current start of injection, which it needs for optimal engine control. Inside the common injector holder is a coil of the nozzle lift sensor of the sprayer needle, in which the extended pusher stick moves. Spray needle movement (injection process) induces voltage signals in the coil depending on the speed of movement of the needle, which are disproportionate to the size of the sheer. These signals are processed directly by the controller. The exceeding of the threshold speed is the signal of the beginning of the injection. Excessive play in guiding the push rod, caused by wear or too loose manufacturing tolerances, cause, that the follower rod moves in the sensor coil in an uncontrolled manner. Consequently, the number of injection signals sent to the controller is greater than the actual number of injections. This leads to an occasional or permanent loss of ignitions, which is a symptom of the fault described here. Sensor repair is not provided or impossible by workshop means.

You can also perform a visual inspection of the electrical wiring of the sprayer needle lift sensor, and in particular a plug connector between the injector and the engine wiring harness. In addition to the well-known rodent damage to electrical cables or during assembly (crushing, Deadlock, abrasions), reason for insufficient contact, and therefore wrong signals, there may be burrs created during production or assembly (non-axial pressure when snapping in or slightly bent contacts). Thus, the needle lift sensor itself does not always have to be the actual cause of the fault!