TECHNICAL BULLETIN
Document number: T0068
For further technical information regarding testing, repairs or to search for New or Remanufactured
Automotive electronic products, please visit www.injectronics.com.au, call our office on (+613) 8792 6999,
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Make: Various
Model: Various
Subject: Tachometric relay
As a result of continual enquires regarding the operation of tachometric relays, the Injectronics technical department have
provided the following breakdown of its operation and terminals. This relay was used on Bosch LE Systems on vehicles such as
GMH JD Camira, VK Commodore, Ford XE Falcon, BMW, Citroen, Volvo, Peugeot and many other European makes.
In brief the tachometric relay is used to supply battery voltage to the entire EFI system and it does this via two different
methods. Initially when the engine is cranking, supply voltage from the starter circuit is used to energise the relay. When the
engine is running the relay contacts are held closed by sufficient primary ignition signal pulses delivered directly from the
ignition coil negative terminal. Having the relay energised in this way also acts as a safety precaution because if the engine
stops, the fuel pump and EFI system power supply would then be turned off.
The tachometric relay consists of seven terminals, which are connected and marked as follows:
Relay Pin 30 – Battery supply: Connect to battery positive usually via a fusible link. This circuit should have battery voltage at
all times.
Relay Pin 15 – Ignition supply: Connected to ignition key on circuit. This circuit should have 10-12 volts whenever the ignition is
on.
Relay Pin 1 – Ignition coil signal: Connected to the ignition coil negative terminal & is used to hold the relay contacts closed
when engine running.
Relay Pin 50 – Starter signal: Connected to the starter circuit and is used to energise the relay when cranking. Should have 10-
12 volts when starter is engaged.
Relay Pin 31 – Relay earth: Connected to ground and voltage should be less than 0.3 volts at all times; with a resistance to
ground of less than 5 ohms.
Relay Pin 87 – Power supply to EFI system: Connected to all EFI related components, which require a 12 volt, supply. Whilst
cranking or running, battery voltage should be present.
Relay Pin 87b – Power supply to fuel pump: Connected to the positive terminal of the fuel pump. With the engine cranking
and running, battery voltage should be present.
31 50
30
15 87b 1
87
T0068.doc
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consequences of anything done or omitted to be done by any such persons in reliance, whether whole or partial upon the whole or any part of the contents of
this publication. Injectronics Australia Pty Ltd. © Copyright 2001.
