The Fuel Pump Relay
This type of relay is known as a tachometric relay, which means that it only responds and sends a voltage to the pump when the engine is cranking or running. The relay receives a signal from the negative terminal of the coil - this confirms that the engine is turning.
This type of relay is used as a safety device: if the vehicle is involved in an accident when there is a possibility of a fuel line being fractured, the engine will stop due to a lack of fuel, the signal from the coil stops and the supply voltage to the pump is removed.
Typical fuel pump relay connections are as follows:
Terminal Number
Connection
30
Permanent battery live
31
Earth
1 or 31b
Coil negative
15
Switched 'Ignition on ' voltage
87
Output to fuel pump
NOTE :- while the connections are correct for certain vehicles, the appropriate pins must be identified before testing. Certain relays also perform a pressurisation purge by allowing the pump to run for a second before shutting off, to prime the system.
The location of the relay will vary between motor manufacturers and is in no set position.
When fault finding or fuel pressure testing it will be necessary to have the pump running when the engine is stationary, this can be achieved by bridging terminals 30 and 87 with a small length of wire. For safety reasons it is good practice to insert a ten amp fuse into the bridging wire.
If the engine runs for a while but then stops, failing to restart for a few minutes, feel the relay to see if it is getting warm as this could be the faulty area. Bridging with the fused link wire will confirm the problem.
CAUTION :- do not be tempted to by-pass the relay by bridging between terminal 15 (switched live) and 87 (fuel pump) as this will start the car, but is potentially dangerous.
מדובר על הריליי של המשאבת דלק.
השאלה מתיחסת לגבי הפיסקה האחרונה בטקסט.