No fuel pump priming noise when key is in. Cranks but won't start

[jayden.world]

Hi all.

I have a B7 S4 but I believe this issue is universal across B6 & B7 platforms regardless of the model.
Therefore I'm leaving a post here to get some wisdom from B6 members.

Audi is giving me another headache.

The car has been sitting for 1 year and 1 month now.

I was hearing some robotic/machinery like high mid-high to high pitched humming noise from rear areas
and I thought maybe it was normal but then apparently it was most likely a fuel filter issue according to my research.

I've been turning on the car regularly like every 1-2 weeks during the COVID and the car had no problem turning on.

However, when I tried to turn on the car yesterday, it cranked strongly no problem but won't start at all.

One thing I noticed was, I did not hear any kind of that whirring/low bass humming noise from the rear, which I assume is the fuel pump priming noise.



So according to my research, it seems like this is very likely to be the fuel pump which I hope is not due to the price of the fuel pump but

do you think changing the fuel filter and the fuel pump relay "614" behind the driver's side fuse box inside the car, not by the ECU box in the engine bay, would do the magic and revive the fuel pump?
Or do you think the fuel pump is RIP due to me ignoring that high-pitched humming noise?

I also read someone saying that if the gas tank is at 1/4, maybe filling up the gas would do the magic but even at 1/4, I should hear the priming noise, no?

Please let me know.

Thank you.

[egovreau]

1/4 tank of fuel should provide enough adequate cooling of the pump. Adding more fuel isn't going to resurrect the pump.

Routinely running the tank close to empty is hard on the pump as it relies on the fuel around it to prevent overheating. If the pump started squealing, there wasn't much that could be done except wait for it's death.

If you can rig a way to directly power the pump with 12V, that will give you an indication of whether or not it works.

As you mentioned, you should hear it run for a few seconds when you turn on the key. If not, the likely culprits are the relay, fuse or the pump.

Check continuity of the fuel pump fuse. If it's good, and since you've already replaced the relay, it's most likely the pump.

Oh, and a new filter won't resurrect a pump either. When the filter starts to clog, it will manifest itself in an almost misfire-like manner, mostly when revving the engine while stopped or accelerating.

Sent from my SM-G986U using Tapatalk

[grayjay]

Use a voltmeter to see if wires into pump are supplying power to the pump, that should either confirm or rule out any problem with relay. Over the years I have had a couple of different fuel pumps die leaving me stranded by roadside. In both cases when I got the pump removed, the pump motor seemed to just get stuck and I was able to get both of them pumping again by tapping on the pump body with a wrench. While this was good for diagnosis or temporary emergency use, fuel pumps are essentially an expendable long term maintenance item. To avoid the risk of getting stranded again, I would not re-use one of the "resurrected" fuel pumps. Replacements are just not terrible expensive (check ebay) and it worth the peace of mind to have a more reliable car and to avoid needing to repeat the unpleasant job of removing and replacing the pump from the tank, breathing and coming into contact with gasoline.