motronic fuel pressure question

[alanmcg]

is the electric fuel pump on a motronic 1.3 supposed to stay on (indefinitely) when the ignition key is on? this seems like a serious hazard, as in the event of a crash, that pump would pump away, which could easily then be followed by a very big bang.

i would think the way its supposed to work is that system pumps initially until a certain pressure is reached, then shuts off.

any insight greatly appreciated.

 

[x_atlas0]

As I understand it, the pump runs continuously in order to maintain pressure, then the fuel pressure regulator dumps the excess back into the tank.

The main issues with what you are describing are the lack of a fuel pressure sensor. There is no way for the pump to know when the target pressure is reached.

 

[Sven]

Yes, pump is on when engine is running. I believe some fuel injection systems (like MS) will shut off power to the pump if the key is on and the ecu no longer senses the engine turning. Does Motronic do this? IIRC your car also keeps the pump running when the key is turned to the ON position but before starting. Not sure how to fix that.

If M1.3 does not shut off then you can get a "crash switch" to put in line with the 12v supply wire to the pump. I have one in my trunk. A serious jarring motion will break the connection. There is a reset button.

 

[Arde]

When I read how my 77 E24 Bosch system worked I recall there was a mechanism for shutting down the pump when the engine stopped. I guess a crash where there is a fuel leak but the engine still runs may result in a BANG. The pump probably stops after the BANG when the wires get damaged.

 

[sfdon]

Starting in the late 70s ? American cars had to shut fuel pump off when engine was not running.
Exemption for cranking.
Keeps the pump from running in an accident.


Csi gets a ground signal to fuel relay from pin 19 at the ecu.

Jetronic has a switch in the AFM. Door closes and pump stops.
Combi relay has a black/relay

Motronic 1.0 and 1.1 has a sensor on the flywheel that counts teeth.
Each passing tooth produces a voltage. When the ecu sees no voltage
it turns off the fuel relay ground. One missing tooth can cause the pump to go
on and off each rotation.