The problem might be that with the new pump there is just the right combination of flow, pressure. pulse, that the syphon jet relief valve is oscillating, it sits in the fuel pump well but pulsations from that will travel back through the return hose. It's a long shot but also a strange problem ;) Was the fuel filter/regulator replaced or lines taken off, is the syphon jet working? Now that I think about it there could be a kinked or restricted line, did you have the syphon jet out before?

Fuel pressure gauge ordered, night try swapping the fuel filter back again see if that shuts it up?

Yeah fpr and filter was replaced, then pump, didn't have Syphon jet out until today, removed it to check tho oring etc mentioned in other posts, all looks good, put it back together, fired it and noticed actual hose is buzzing like mad. All the lines I can see look alright

Non run/start issue?

If needle vibrates at rail = FPR if pressure stable at pump also FPR.

It feels like FPR is oscillating which shouldn't happen but as engine pulls pulses of gas there will be a differential pulse going back to siphon jet. I've jest never heard of it being audible.

You should be able to figure it out with some Ts and some hose clamps. Tap into output from pump and input to siphon. I think that's supposed to be 1.3bar bar (whatever that is in psi) and from the pump I'm guessing 60-70 to have excess after dropping to 50.00 through the FPR.

Fuel pressure gauge needle vibrating with engine running means that there is no air in the system up to the gauge so nothing to do with anything else for diagnostics. The pressure at the pump, rail, gauge will all be the same pressure unless the fuel filter is plugged. The fuel pressure regulator is set to about 40+ PSI so engine running rail pressure will be about 50 PSI because the syphon jet relief valve will add about 8 to 10 PSI which is what the return pressure is. Just wanted to clear up the confusion.

Did you re-use the accordion section of hose from the fuel pump to the top of the sender ??
Back in the day there was often a snubber in the section of line where the accordion hose is on the E53 so if you replaced that section with something else maybe that is a problem.

I didn't change any hoses when replacing fuel pump or filter/fpr.

Hot start issue m62tub44
 

https://share.icloud.com/photos/0f8i...EPAWpYx_4K2eRQ
Before replacing FPR

https://uploads.tapatalk-cdn.com/202...a5a9165709.jpg

https://uploads.tapatalk-cdn.com/202...d1adb025c1.jpg

49.5 ± 1.3 psi

https://share.icloud.com/photos/0923...JfrqfvGIq4Snmg
After replacing FPR

49.7 It ± 0.3 psi at idle. Also 13 psi after 19 hours.

With W.O.T. I measured about 1psi drop followed by 1psi boost when let off throttle. Saw about 0.3 psi boost on moderate throttle but steady

So 2psi less swing at idle with the fixed FPR o-ring.

No idea where you came up with 40psi. It's known that E53 runs on 50psi and uses milliseconds of injector timing to measure how much fuel per stroke to calculate how much fuel. I don't recall different part numbers for the different engines so I think they all run at 50 psi.

≈ 19 psi is the expected return to the siphon. I don't know if there is additional psi overhead but I suspect there is so rather than 50+19=69, I would possibly expect 80-90 psi at the pump.

When the pump gets weak, it won't supply enough overhead for the siphon and that will give you the same symptoms of a bad siphon o-ring.

Weak psi is the normal ends of life of an electric pump. Unfortunately it's masked by the FPR and worse, also from the fact most people refuel before the siphon jet failure will present itself.

Example: my wife "ran out of gas" with 1/4 tank showing, my dad brought her a Jerry can of fuel and the car started. They decided must be the gauge reading wrong so wife just never let the tank get below 1/4.

She never told me so I got to experience the same, however, at 6°F on a freeway, TWICE.

(Had additional problem of cam sensor, thought that was the only problem due to aforementioned keeping the secret, so a week later car stalled on freeway yet again with 1/4 on the gauge)

Both our e53 suffered the same o-ring siphon failure at 130 ± 3 (k miles).

Wife's FPR failed at 170-180k but mine never failed though 205k.

Both had fuel pump fail almost exactly 5000 hours.

No idea what you are talking about with siphon jet relief adding psi.

There's a relief valve for if there's too much return pressure to the siphon that will vent excessive pressure directly back to the right tank.

With literally 40-50 hours of research on this fuel system never saw one ¶ describing what the relief pressure is where that valve opens and it's implied by BMW it doesn't open under normal use just in case of extreme such as siphon jet pump foot gets plugged.

From BMW : 3.45 bar to engine 1.3 bar to siphon. (never found what is expected from the pump and never needed to directly measure myself).

Educated guess of 70-100 psi (4.8-6.9 bar).

The numbers given above are not accurate for the e53 and the concept of pressure being the same before/after the FPR is also not accurate.

The entire point of the FPR is to take the pump pressure which is by design excessive and regulate it down to what is needed by the engine.

The type of injectors on the e53 are such that they require a known quantity for pressure so they can determine the fuel amount using milliseconds of pulse. A 1 psi differences at the rail will make for a 2% error in fuel supply. Not a problem for the ECU to figure out how much fuel trim to add or subtract to get the air fuel mix to 14.7.

@ Andrewwynn
Is there an X5 sight that you don't post on ?

I monitor about 3-4 but xoutpost is the main one.

I also monitor F10 (wife's) and my current car is E70 but there's much more activity on E53 and I have more experience fixing that chassis.

I was hoping that maybe I could escape from some of your BS and full of yourself attitude but since you are "monitoring" it's unlikely.