Odd fuel line noise

[taznuv]

I've had for a while a problem with noise from my BMW E46 325 which I was concerned was the fuel pump. I asked my garage (independent) for their opinion. They had in on the ramp and say the pump sounds perfect, and think the noise is coming from the fuel lines themselves. They suggested it could be the pressure regulating valve or the non return valve in the pump, but admitted they had never heard anything quite like it. The noise is noticeable when sitting idling, sounds light and metallic, changes slightly with revs, but not directly. Almost sounds like a central heating pump when there is air in the system. You don't here it when the pump does it's initial run when turning on the ignition. I presume there were no leaks or loose fittings or they would have attended to them.

Apart from starting to switch components I don't really know what to try next. Anyone heard anything similar?

thanks

Bruce

Edited by taznuv on Wednesday 15th April 11:16

[bertelli_1]

Does the car run / drive ok? Could there be something else loose / vibrating & transmitting the noise along the fuel line?

[taznuv]

Yes, should have mentioned the car drives fine.

[greyish]

Any resolution to this?

I have a 99 Z3 2.8 and it seems to have the same issue. Pre-start pressurising of the fuel line sounds fine, not getting any codes for an air leak or fuel mixture issues. But the fuel lines sound loud. Noise just started a week ago for no discernible reason.

The light metallic sound is there as well, I've noticed it in the 1k to 2k RPM range.

I really hope that you have found the problem as this is certainly the same problem I am having.

Edited by greyish on Thursday 18th June 20:46

[taznuv]

Hi Greyish, sorry no resolution to this one. I have found that on mine and possibly yours the regulator is part of the fuel filter, and therefore closer to the cabin than on other cars. Therefore I'm going to try a new filter/regulator as an experiment sometime, will post back. If you find anything please let us know.

[tristancliffe]

Could it be a heat sheild on something vibrating. Exhausts and fuel lines often have thin pressed shields that are great for a few years, but as they age they seem to make more and more noise, peaking shortly before they fall off (usually leaving rusty bolts that you can't budge behind!).

[GavinPearson]

When I spent some time in Powertrain NVH we had this exact issue on a new model year vehicle we were about to introduce. We went over the whole vehicle looking for something wrong, in the end the solution was to fit a more flexible hose (had fewer steel braids in it) and that fixed it. Provided the pump is delivering fuel reliably, and the fuel regulator / damper is working OK, don't worry about it unless the noise is getting on your nerves, in which case fit more flexible lines and decouple the pipes from the body as best you can.

[CNHSS1]

interesting about the flexi pipes, my racer makes a funny noise which seems to eminate around the adj fuel pressure reg area, but only when 1st started in the paddock from cold. The mapping is less than perfect due to the cold start temp correction (not spending time or money mapping for 3mins on start of an event!). id been keeping my eye on the noise/problem expecting something to fail in the near future due to the odd nature of the noise, but its still going strong 2 years on! the hi pressure pipes are rather stiff, so maybe its a combination of the low cold idle, lumpy running and the stiff pipes transmitting the 'noise'.
another mystery solved, cheers

[GreenV8S]

The FPR on mine makes a curious squeak when the pump first starts up, never noticed it while the engine was running. I assume it's some sort of resonance inside the regulator.

[2woody]

everything has a natural resonance frequency - if your pipes' frequency is the same as the fuel pump, then they can "sing" quite markedly.

It is unlikely that BMW will have signed-off the vehicle with this, so I'd look for missing parts, such as a fuel pipe clip or a fuel pressure damper. The damper, if its fitted, can live near the filter and I've known them to be thrown away with the filter and not replaced.

failing that, changing the fuel pipe material is sensible, provided it's at the same end of the car that the noise is coming from.

[taznuv]

thanks all for the replies, gives me some good ideas of things to look at, and also is reassuring that it's not likely to be a serious problem