Fuel filter change, noisy fuel lines?!

FlaatusGoat

Earlier this month I changed the fuel filter in my 1.5 DCI K9K engine (NV200) and it's driving beautifully. But, that's where the good news ends. After 20 or so miles and over the usual engine noise this faint but present 'whine' developed in the background. Usually it gets to full pitch once the engines started to warm up. Whilst annoying, I really don't want to total my HP pump in the long run. So, to establish the source of the noise I decided to invest in a stethoscope. Lo and behold, I've isolated the source of the noise to the two fuel lines that run into the engine. Bingo.

I can't fathom how simply changing a fuel filter would cause this. But regardless, any suggestions on how to 'fix' this annoying whine....

Goudy

Haven't we been here before?

Goudy said:

This engine is shared with Renault and there are some posts relating to similar problems on Renault forums.
Most noise problems after changing the fuel filters tend to be pipes vibrating due to small air leaks.

It's the fuel pipe/s vibrating due to air entering the fuel system.
Air is being drawn into the fuel system somewhere, it's very common if you check other forums for vehicles fitted with this engine (Renault and other Nissans).

As you have had the fuel filter off, that's where to start looking.
Are the pipes to the filter seated properly and in the right order.

What filter did you use? 
Some cheap copies aren't made particularly well and the fittings might be dodgy.
The ports on cheap filters (the stubby hard pipes) can also be mis shaped or be of the wrong size.

You can do a basic check, test the fuel line to the filter from the tank.
Do that vibrate as well?
If so it's likely picking up air from the tank, likely due to the in tank LP pump/strainer inside being clogged.

If it's only vibrating from the filter to the HP pump, it's drawing in air forward of the filter.

The two pipe from/to the engine from the filter are part of the same loop, fuel passes through the filter to the HP pump, onto the rail and injectors and then the spill off returns to the filter, that's why two pipes might be vibrating.
The main feed pipe and the spill off return back the filter, as air is looping around and around.

FlaatusGoat

Goudy said:

Haven't we been here before?

Goudy said:

This engine is shared with Renault and there are some posts relating to similar problems on Renault forums.
Most noise problems after changing the fuel filters tend to be pipes vibrating due to small air leaks.

It's the fuel pipe/s vibrating due to air entering the fuel system.
Air is being drawn into the fuel system somewhere, it's very common if you check other forums for vehicles fitted with this engine (Renault and other Nissans).

As you have had the fuel filter off, that's where to start looking.
Are the pipes to the filter seated properly and in the right order.

What filter did you use? 
Some cheap copies aren't made particularly well and the fittings might be dodgy.
The ports on cheap filters (the stubby hard pipes) can also be mis shaped or be of the wrong size.

You can do a basic check, test the fuel line to the filter from the tank.
Do that vibrate as well?
If so it's likely picking up air from the tank, likely due to the in tank LP pump/strainer inside being clogged.

If it's only vibrating from the filter to the HP pump, it's drawing in air forward of the filter.

The two pipe from/to the engine from the filter are part of the same loop, fuel passes through the filter to the HP pump, onto the rail and injectors and then the spill off returns to the filter, that's why two pipes might be vibrating.
The main feed pipe and the spill off return back the filter, as air is looping around and around.

Appreciated, this is very informative. Ah and yes whereas before I simply didn't have a clue where the hum/whine was emanating from, the stethoscope has basically pin pointed it. Great cheap bit of kit. So the fuel filter I got was a bit more expensive, hence trying to avoid the Chinese kit. It's a Mahle with made in Austria stamped on it. All the fuel lines were connected to it identically to the previous filter. They're push fit style hoses that clip on.

I'll go back under the van and try and hear if the hose noise is present on the lines that go before (to the fuel tank) or after the filter (to the hp pump)

I read somewhere else that a bit of vaseline can help seal any tiny imperfections on the fuel filter's pipes. Might applying a bit of that, or some silicone grease be beneficial?

Goudy

There will be a rubber o ring inside the fittings on the end of each hose.
Look inside the push fit fitting to see if they are damaged.  You might have to shine a torch in the ends.
Broken, twisted or flaky rubber and they won't seal.

If they look ok, refit them. You can use a spot of vaseline or silicone if you think that will help.
Push them on and they should click into place and feel quite firm.

If they wobble or rock about, that suggests there's a discrepancy in size between the port on the filter and the fitting. 

Some fuel filters have a water drain on the bottom, make sure it's done up finger tight, but don't over tighten with grips or anything like that, they are usually plastic and can snap off.

There's a priming blub on these somewhere (hatch under the seat??).
Pumping it should prime the fuel after any of the system have been open.

You can also pump/feel it as it's running, it should become hard when running as it's full of fuel.
A soggy, soft feel when it's pumped a few times running means there's definitely air in there.

I wrote on the other thread some vehicles just don't like certain filters.
I've come across more than one model that only liked genuine or OEM filters.

I've chased a fair share of air leaks in diesels to know they are really frustrating. 
Though it's hard sat here to help more, I would stick with the principle of "the last thing fiddled with" until I could prove beyond doubt it's not that.

I have in the past, used the bypassed method to trace an air leak.
It was an old Citroen TUD that had a screw on filter that went into the end of the cylinder head (to help warm the fuel).
I ended up bypassing chunks of the fuel system at a time with a long piece of hose from the tank forward until I found the leak. (warped surface where the filter screwed on).
I ended up just bypassing the standard filter with a large plastic fuel filter.

But writing that, it would be a bit tricky to do this with yours as the spill off returns to the filter and not the tank or HP pump.
You'd have to do some serious plumbing to bypass the standard filter.