Tachometric Relay

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Page created by T Feb 13th 2015:

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The pinout of a Durite  EFI VK Tachometric Relay is shown. Image by T. Click to Enlargen.
EFI VK Tachometric Relay Pinout. Image by T. Click to Enlargen.
Bosch EFI VK Tachometric Relay circuit. Image by T. Click to Enlargen.

Tachometric Relay:

A Tachometric Relay is used on EFI powered cars to control the fuel pump.  Any event that causes the engine to stop causes the relay to turn off the fuel pump thereby preventing fuel from being continuously sprayed into the engine bay and causing a fire. It is also used in LPG powered cars for similar reasons.

Operation:

The Relay's internal electronics are  powered from the +12v ignition circuit, so the ignition key must be in the ON position for the Relay to work. The Relay can then be activated by the starter activation wire when the ignition key is in the START position. For as long as the key remains in the START position, the Relay will remain on. The Tachometric Relay also works by monitoring the voltage on the coil negative. The presence of a recurring +48 volt level, signals the Relay to stay on. The absence of a +48 volt level, signals the Relay to turn off about 1 second after the last +48 volt pulse.

Spare Tachometric Relay:

It is always advisable to carry a spare known working Tachometric Relay. These are known to fail without warning and at any time.

Replacing The Tachometric Relay:

Make sure the ignition is turned off before unplugging or installing the Relay.

The Intermittent Tachometric Relay:

Tachometric Relays can become termperature sensitive, meaning they might fail when they become hot. Alternatively they might only work when they become hot. Observe the temperature of the Relay at the time of its failure.

Connections And Socket Checks:

     

  These checks can be made with the Relay unplugged.  
Pin Number 
Pin Voltage    Pin Function 


 
Pin 1 +12v only with the engine stopped and the ignition ON  Coil -ve
Pin 15 +12v only when the Ignition is ON and also when the ignition is in START positions 
 Ignition
Pin 31 Ground - permanently grounded - Meter to Battery -ve 0 ohms
 Ground
Pin 30  +12v Permanently Live
 Battery +ve
Pin 50  +12v only when the Starter is activated
 Starter



 

                   These checks can only be made with the Relay plugged in                  
 
Pin Number 
Pin Voltage Pin Function
     
Pin 87 +12v under cranking and normal running
ECU and Injectors
Pin 87b +12v under cranking and normal running
Fuel Pump
     

 

Testing The Tachometric Relay While It Is Plugged Into The Car:

While still plugged into the car, the relay must be heard to click on when the ignition key is moved from ON to START and off again when the key is turned back to ON. If not, try replacing it with another Tachometric Relay. If the replacement does not work either, check fuses and earths. After fixing the problem, reinstall the original relay to check its integrity. If the Relay clicks on but the Fuel Pump does not start the fault may be burned contacts inside the Relay. Check the Fuel Pump fuse. If intact Replace the Relay and try again.

Fuel Pump Warning Light:

Fuel Pump Warning Light is a good way to monitor the Tachometric Relay.

Fuel Pump Failure Circuit. Image by T. Click to Enlargen.

Testing The Tachometric Relay While It Is Not Plugged Into The Car:

These tests can be done when the Relay is not plugged into the car,

Activation Under Cranking:

To test that the Tachometric Relay works during cranking, connect pin 31 to the -ve terminal of the car's  battery and pin 15 to the battery's +ve terminal. Next connect +12v to pin 50. The Relay must active and deactivate every time +12v is connected and released from pin 50.

Testing Pin 1:

Pin 1 is the Coil -ve connection, and when the Relay is not plugged into the car, a +48 volt source is needed to test this pin's functionality.  One way of generating +48 volts is to use 4 capacitors. Charge each of them to +12 volts by placing them across the car's battery, then connect them in series to get +48 volts. *Caution*: Don't allow any part of your body to come in contact with the +24 volt, +36 volt or +48 volt connections.Insulated alligator clip leads are a good way of connecting the capacitors in safety.The lowest capacitor's -ve leg is connected to pin 31 and the highest capacitor +ve leg to pin 1. The Relay must then activate and stay activated for many seconds, depending on the size of the capacitors until the capacitors discharge or are disconnected. An alternative method is to use 3 capacitors. Charge each of them to +12 volts by placing them across the car's battery, then connect them in series to get +36 volts. *Caution*: Don't allow any part of your body to come in contact with the +24 volt, +36 volt or +48 volt connections.Insulated alligator clip leads are a good way of connecting the capacitors in safety. The lowest capacitor's -ve leg is connected to pin 15 and the highest capacitor's +ve leg to pin 1. The Relay must then activate and stay activated for many seconds, depending on the size of the capacitors until the capacitors discharge or are disconnected. 1000uf 63 Volt electrolytic capacitors will do the job.

Connecting capacitors together to test the functionality of pin 1 on a Tachometric Relay as used in the EFI VK.  Image by T. Click to Enlargen.

Typical Tachometric Relay Failure Causes:

These can be dry soldered joints which are easy to spot. Electolytic capacitors degrade with under bonnet heat exposure. Tantallum capacitors degrade with under bonnet heat exposure.

Bosch EFI VK Tachometric Relay:

The Bosch 0 280 230 005 Relay uses an NE555 timer chip and discrete components. With the Coil -ve disconnected, it does not stay activated for 1 second after START is deactivated. It immediately turns off. This Relay drops out a 6 volts.

Bosch EFI VK Tachometric Relay Static Impedance Checks:

A good Bosch Relay will measure between 5M ohms and 6M ohms when the red lead of a Digital multimeter is connected to pin 50 and the black lead is connected to pin 31. A good Bosch Relay will measure close to 39K ohms when the red lead of a Digital multimeter is connected to pin 1 and the black lead is connected to pin 31. If a Relay passes the static tests it may still be intermittantly faulty due to a temperature sensitive component. If a Relay fails the static tests it should be considered faulty and be repaired or replaced.

Bosch EFI VK Tachometric Relay circuit. Image by T. Click to Enlargen.

Durite EFI VK Tachometric Relay:

The Durite 0-723-22 Relay uses discrete surface mount components. With the Coil -ve disconnected, it stays activated for 1.5 seconds after START is deactivated. This Relay drops out a 7volts. The Durite 0-723-22 Relay is a replacment and is also used in Opel 1238566, 1238563, 1238566 GM 90124673, 90158189, 90158443, 90213542 Lucas FDB 501

Durite EFI VK Tachometric Relay Static Impedance Checks:

A good Durite Relay will measure about 1.5 M ohms when the red lead of a Digital multimeter is connected to pin 1 and the black lead is connected to pin 31. A good Durite Relay will measure about 1.2 M ohms when the red lead of a Digital multimeter is connected to pin 50 and the black lead isconnected  to pin 31. If a Relay passes the static tests it may still be intermittantly faulty due to a temperature sensitive component. If a Relay fails the static tests it should be considered faulty and be repaired or replaced.  

Tachometric Relay Performance Figures:

 

  Tachometric Relay 
  Drop Out Voltage 
   Min Pull In Voltage 
 Durite 0-723-22
3.5 7.0
 Bosch 0 280 230 005
3.5 6.0

 

KAE EFI VK Tachometric Relay:

KAE Relay 3304500 will also do the job. Internal details of this Relay are not known at this time.

The Durite Tachometric Relay as used in the EFI VK. The underside uses Surface Mount Components. Image by T. Click to Enlargen.
Durite EFI VK Tachometric Relay. Broken solder joints can appear at the left side of the picture where the contacts meet the circuit board. Image by T. Click to Enlargen.
Durite EFI VK Tachometric Relay circuit (under side). Image by T. Click to Enlargen.
 
Durite EFI VK Tachometric Relay circuit. Image by T. Click to Enlargen.
Durite EFI VK Tachometric Relay circuit. Image by T. Click to Enlargen.
KAE 3304500 EFI VK Tachometric Relay. Image by HJ Paul. Click to Enlargen.
 
 

 

Workaround:

If the Engine won't start because the Relay hasn't activated, try having a 2nd person crank the Engine while you tap the case of the Relay. Internally the Relay can become voltage sensitive and a Tap can shock the Relay's Armature into make contact.

Links:

Fuel Pump Warning Lamp

Durite 0-723-22 Tachometric Relay Supplier

Durite 0-723-22 Tachometric Relay Supplier

KAE 3304500 Tachometric Relay Supplier

Bosch 0 280 230 005 Tachometric Relay Supplier

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