Fuel pump priming

[Waffles_s4]

The fuel pump does not prime when opening the door at cold start (fuel system un-pressurized).

[JoeAWD]

A lot of cars will not turn on the fuel pump until they see the engine turning. On one car I own we take off the cam sensor and turn it by hand to get the fuel pump to prime.

Few options:

Jumper fuel pump relay?
Disconnect coils and try to start?

[Waffles_s4]

On the b8 and b8.5 s4/s5/etc when u open the driver door, the fuel pump automatically primes. It won't prime anymore for some reason though.

It even does that on my q5 2.0t

I have no clue where is the fuel pump relay. Any clues?

I can try to start it without the coils, it should prime at that point. But am trying to prime it without cranking the engine.

Maybe the fuel relay is not working?

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[JoeAWD]

Are you sure? I thought it just kick on the IC pump when you open'ed the door.

found this:
https://www.audi-sport.net/xf/attach...ions-pdf.83833

[Waffles_s4]

Still not priming when opening the door... Did it ever happen to anyone?

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[Waffles_s4]

Bumping for answers

[theweebabyseamus]

Fuel pump will prime when you open the drivers door.

[Waffles_s4]

Fuel pump will prime when you open the drivers door.

I know, but its not doing that anymore for some reason and am trying to find why

[Johnson]

Did you scan for any codes using a generic scan tool? Maybe something else is unplugged

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[Waffles_s4]

Did you scan for any codes using a generic scan tool? Maybe something else is unplugged

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I did, nada

[Johnson]

Do you have VCDS? There is an option there, I think in basic settings, to activate fuel pump. I used it to drain my tank once.

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[Waffles_s4]

Do you have VCDS? There is an option there, I think in basic settings, to activate fuel pump. I used it to drain my tank once.

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Again, am trying to get the fuel to prime when I open the driver door. Thats it, the rest is all good, car starts, etc.

[Waffles_s4]

Bumping for suggestions

Checked all relays and fuses - all good

[kelseysautobody]

Bumping for suggestions

Checked all relays and fuses - all good

What are your conditions to think the fuel pump is not priming? Long crank to start?

[Waffles_s4]

What are your conditions to think the fuel pump is not priming? Long crank to start?

Yes on cold starts, as well as the fact that I dont hear the fuel pump priming when opening the driver door anymore.

[B8s]

was a fix ever found? I have the same issue.... cark cranks but wont start. I dont hear the fuel pump priming when I open the door...

[B8s]

Bump? My fuel pump wont prime at all. Car cranks but wont start

[Smac770]

Did you check the fuse? Panel C (driver's end of dash), column 2 (middle), fuse 3. Could also be a fried J538 pump controller or a a dead G6 transfer pump. Did you scan for DTCs?

[B8s]

its def not the fuse. Its not throwing any codes

[Smac770]

Suggest you directly power the pump with 12v (B8.0 uses a single-phase Bosch pump, so you can just power it directly and make it pump) such as when doing the pressure and throughput tests as documented in the Fuel Supply workshop manual (erwin.audiusa.com). If the physical pump tests within spec for pressure and throughput, and operation, then it goes back to the control of the pump. Maybe there's a break in the line from the J623 (ECM) to the J538, over which the J623 sends a PWM signal to signify the pump duty cycle, so the J538 is sitting there ready but sees no command to operate.

On the 5-pin plug of the B8.0 J538 is pins 1 and 2 power the pump, pin 3 is 12v from the car, pin 4 is ground, and pin 5 is the command line from the ECM. See if you can register any voltage backprobing pin 5. I presume you've monitored the high pressure rail fuel pressure and see it low and not pumping up when cranking.

Looking at the wiring diagram, it appears you have a G410? They removed that on the gas only 2.0T. G410 monitors the low pressure side fuel pressure. So what's that say? And we presume the value fails to pump up when you open the door or crank the engine. Maybe something is wrong with that sensor and it's saying "yeah, I've got pressure, no need to prime" when in fact there is none.

[mcoomer]

I don’t wish to hijack the thread, but is G410 normally open or closed? I’m assuming it’s closed at low pressure and opens when normal operating pressure is achieved, so 5V to the ECM when the pump should run, and no volts when pressure is achieved.

[Smac770]

G410 is a pressure sensor, not a pressure switch like the oil switches. So it provides a measurement, not a on/off state based on being above or below a physical set point.

Review pages 54 and 55 of Audi SSP 411 for info on the EA837 G410 and G247 fuel pressure sensors.

[mcoomer]

G410 is a pressure sensor, not a pressure switch like the oil switches. So it provides a measurement, not a on/off state based on being above or below a physical set point.

Review pages 54 and 55 of Audi SSP 411 for info on the EA837 G410 and G247 fuel pressure sensors.

Found it. Makes sense that it’s constantly outputting a signal to the ECM. A simply on/off wouldn’t require a PWM pump. Thanks for the info.