Diesel injectors with needle sensor

Diesel injectors with needle sensor

Diesel injectors with needle sensor work by sending a signal to the ECU which then controls the fuel pressure pump and instructs it to send fuel to the injectors

Electronic diesel control systems use a needle sensor injector

If one of your injectors has a wire running from it your system is (probably) of the needle sensor type. These systems will often have a fuel pump with electronic control built in to them.

The important parts inside the needle sensor injector are:

  • a pin which moves (inside a coil) under fuel pressure and makes a circuit  – if this is jammed it won’t signal properly
  • the coil – built into the injector – if this is faulty it cannot signal  properly.

If the injector nozzle is jammed or seized the small rod which operates the needle sensor system will not be able to operate correctly. Therefore check needle valve in nozzle is operating freely read more

There is a small coil, built into the injector,  which sends the signal to the ECU

You can often check this coil

injector with needle sensor components is sound by checking resistance across the wires from the needle sensor injector. Resistance should be something in the region of 95+ ohms.

Diesel fuel injectors

can be divided into at least 4 different types:

bosch rotary injector


2 stage injector with pilot injection
Pump duse
Common rail

Rotary diesel injection is entirely mechanical.
The only electronic involvement is the pump solenoid which cuts the flow of fuel, and the engine, when the driver switches of the ignition key.

Rotary diesel injectors spray fuel into the engine when pressurized fuel overcomes the resistant of a spring inside the injector.
The injector nozzle within a rotary injector is often of the pintle type.
Rotary injection is often (but not always) of the indirect injection type.
Possibly the most common rotary diesel engine in European cars is the Peugeot XUD9 1.9 diesel and turbo diesel.

VW also made a number of rotary 4 and 5 cylinder diesel engines . Rotary diesel injectors are often distinguished by being screwed into the cylinder head (i.e. they have a threaded section.)

Tdi – 2 stage injection with pilot injection.
These injection systems are what are called semi-electronic. One of the injectors in the system has a needle sensor built in which communicates with the ECU and allows engine timing to be finely calibrated.

2 stage injectors usually have a hole type nozzle. And a 2 spring system.

The primary spring is smaller than the main spring.
When pressurized fuel enters the injector from the fuel pressure pump it first opens the small spring to allow a small pilot injection spray to enter the engine.
As the pressure builds the fuel opens the second larger spring and main injection takes place.

The needle sensor
When the primary pressure is reached and the smaller primary spring opens it  sends a signal to the ECU, by moving the rod through the coil,  that primary injection has occurred. If this needle sensor stops functioning the engine will probably still run but performance will be reduced and a malfunction light will probably light on the dashboard.