Safety stop for fuel pump in the event of an accident
Posted: Fri Oct 03, 2025 4:09 pm
Ive always been a bit concerned about the sensibility of the electric fuel pump running whilst the ignition is on, without the engine needing to be running. In the event of an accident the fuel pump would just keep running which would be a fire hazard if the fuel hose was ruptured.
Meanwhile, whilst doing my EPAS conversion I was looking for a way to prevent the EPAS motor draining the battery if the ignition was ever left turned on without the engine running.
Although different issues they share the same solution.
The addition of an interactive relay made for fuel injected cars will ensure the electric fuel pump (and EPAS motor) can only operate when the engine is actively running.
In operation the relay provides a short burst when the ignition circuit is first turned on but will only continue providing power to the fuel pump if the engine is started. It achieves this via a simple connection to the negative side of the ignition coil. The relay needs to sense active ignition pulses from a running engine and it will therefore cut out if the engine stops or stalls.
Turning the ignition off and on to restart the engine will restore power to the fuel pump immediately in the event of a stall but if the engine stops due to an accident the fuel flow is stopped and stays stopped.
In my own instance Im also using the relay to control the power to the EPAS but I think this is a worthwhile safety modification just for the fuel pump.
The 5 pin interactive relay used was sourced from an early 1980's Ford Capri 2.8 Injection which is where i know it from but the same was also fitted to a number of other vehicles I believe. Compatible part numbers are 6145938 6161570 85AG9P704AA 85GG9P704AA LUCAS FDB502.
These interactive relays are very robust in use but in the event of the relay ever failing and a replacement not immediately available a bog standard 4 pin automotive relay can be substituted which will put the circuit back into manual mode - just allowing the fuel pump to work whenever the ignition switch is on.
Relay connections
31 Earth
1 Negative side of ignition coil
87 Output + to fuel pump (and EPAS)
15 + Ignition Switched live
30 +Permanent, unswitched Live
The easiest way could be to cut the existing white wire to the fuel pump in the engine bay. Take the fusebox side of this wire to terminal 15 of the new relay and the fuel pump end of this wire to it's terminal 87. It is also advised to protect this with an inline fuse given the B's wiring oddly never included any fuse protection for the fuel pump.
Run a new wire from the relay's terminal 1 to the negative side of the coil.
Pick up an unswitched live to run to terminal 30 of the relay.
Run a wire from the relay's terminal 31 to any nearby earthing point.
Meanwhile, whilst doing my EPAS conversion I was looking for a way to prevent the EPAS motor draining the battery if the ignition was ever left turned on without the engine running.
Although different issues they share the same solution.
The addition of an interactive relay made for fuel injected cars will ensure the electric fuel pump (and EPAS motor) can only operate when the engine is actively running.
In operation the relay provides a short burst when the ignition circuit is first turned on but will only continue providing power to the fuel pump if the engine is started. It achieves this via a simple connection to the negative side of the ignition coil. The relay needs to sense active ignition pulses from a running engine and it will therefore cut out if the engine stops or stalls.
Turning the ignition off and on to restart the engine will restore power to the fuel pump immediately in the event of a stall but if the engine stops due to an accident the fuel flow is stopped and stays stopped.
In my own instance Im also using the relay to control the power to the EPAS but I think this is a worthwhile safety modification just for the fuel pump.
The 5 pin interactive relay used was sourced from an early 1980's Ford Capri 2.8 Injection which is where i know it from but the same was also fitted to a number of other vehicles I believe. Compatible part numbers are 6145938 6161570 85AG9P704AA 85GG9P704AA LUCAS FDB502.
These interactive relays are very robust in use but in the event of the relay ever failing and a replacement not immediately available a bog standard 4 pin automotive relay can be substituted which will put the circuit back into manual mode - just allowing the fuel pump to work whenever the ignition switch is on.
Relay connections
31 Earth
1 Negative side of ignition coil
87 Output + to fuel pump (and EPAS)
15 + Ignition Switched live
30 +Permanent, unswitched Live
The easiest way could be to cut the existing white wire to the fuel pump in the engine bay. Take the fusebox side of this wire to terminal 15 of the new relay and the fuel pump end of this wire to it's terminal 87. It is also advised to protect this with an inline fuse given the B's wiring oddly never included any fuse protection for the fuel pump.
Run a new wire from the relay's terminal 1 to the negative side of the coil.
Pick up an unswitched live to run to terminal 30 of the relay.
Run a wire from the relay's terminal 31 to any nearby earthing point.