Fuel Relay #103 -- Is it really necessary?

[jose456891]

Volvo 240 didn't have this fuel relay. Modern BMW does not have this relay.

It is Volvo over-engineer genius that makes your life fun.

+1!

/thread

[mecheng]

I wish I was an electrical eng and could answer you but with all do respect to those that responded
It is volvo over engineering or not needed how can you know for sure unless you know what it does exactly. Maybe it shuts off the fuel pump when it shorts due to failure or something else. I doubt volvo would spend the time needlessly

Just like the heater hose coupler. It is not over engineered. It helps speed up the car assembly and prevents a hot hose burst inside the cabin as someone astute observed. The laymen may not understand but they should also never conclusions based on guessing

[Turbo_Boss]

My Skoda Ocatvia use a similar relay with some electronic inside. They called 409 Fuel Pump Relay

I am pretty sure most of the electronic circuit inside is for primer pump and safety reason.

In my Skoda, the primer pump is trigger when the driver door is open. As soon I open the driver soor in the morning, I hear the relay buzzing primering the fuel pump for a few seconds.......... Maybe this happen on the Volvo and the driver doors triger the circuit.

VW, BMW and MB has some features that when the car is involved in a crash, the car computer shut off the fuel pump, open the door locks, turn on the hazard blinking lights and ofcourse deploy the airbag...............Maybe Volvo do the same.

Isaac


Here is the VW 409 Relay terminal configuration. "Maybe" this help you to undertand how the Volvo relay works.

Terminal 30 - power from Fuse S163
Terminal 31 - ground
Terminal 85 - to Engine Control Module
Terminal 86 - from ignition switch (D15)
Terminal 87 - to fuel pump circuit - Fuses S228, S232, S234, & S243
Terminal C - from crash signal circuit
Terminal TK - from door contact switch circuit

[abscate]

VW software now reprograms the other drivers' GPS data to make it look like they caused the accident , too. It's called the "Fahren Unterscheid 2" option or FU2 for short.

[Turbo_Boss]

VW software now reprograms the other drivers' GPS data to make it look like they caused the accident , too. It's called the "Fahren Unterscheid 2" option or FU2 for short.

[bobray12]

so my question is if its a trigerrable by a preprime key turn to pos II. how does the relay function when car is running.
how does that circutry the creator of this thread talks about keeps the relay closed to keep the fuel pump on.
or is the ecm pulsing power to keep this relay latched.
the problem i am having with mine is a intermittent hard to start when warm.
i am not hearing the preprime happen after i drive the car for a bit,turn it off and 15 orso minutes later try to restart.
i am not hearing the fuel pump kick on.no matter how many times i cycle the key off to II pos.it will start after a very long crank.
the Owners manual says it can take up to 10secs to start. but i just dont understand why

[erikv11]

The. next time you have the problem, remove the relay and use a wire to jumper the socket, use location 15 to location 87. If the jumper solves it then the relay is bad. If it doesn't then the problem is elsewhere like wiring (unlikely but possible) or the fuel pump (more likely).

It can be difficult to hear the fuel pump, you may. want to try a test light or a voltmeter in the pump plug instead. viewtopic.php?t=69221&start=10

Regardless, i'd try the jumper first, find out if the problem is the fuel pump or the relay.

[yanga001]

The vibrator is half the circuit, i have one of those spare and will see if i can take a look at it as well. The fuel pump probably sink's a fair amount of current(by fair i mean multitudes higher then the chip can provide) so i imagine this connects to some sort of coil. I am wondering if the chip is just used to assert a strong output for the coilto sink the necessary current. It may also serve as a sort of isolator for the ECU lines so we do not fry the ECU by stray currents, shorts, etc. Much harder to replace an ECU then the relay, especially when multiple systems are bound to said ecu.

I do not suspect the fuel pump is cycled on and off constantly as that may create more wear on the pump, the coil, and

I think a proper schematic recreation would be necessary to fully understand this circuit along with scoping the signal. Ill see what i can do as i got a spare, scope, and power supply for it. My thought is that this circuit may assert its high signal on trigger enough to allow consistent fuel priming when the voltage bounces on crank/startup.

The complexity may be born out of the necessity to control a fuel pump from an ECU, protect the ECU, and ensure operation in varying voltage environments. One must also remember that not all chips are designed for automotive use so as suggested this may have been the cheapest and most useable circuit they could find.

Will look into this a bit more