Hollow tapping from fuel rail Duff FPR?
 

Hello all, in the midst of winter my 940LPT started making a regular hollow tapping noise once warm, it is heard in the cabin where it sounds like a modern diesel, outside it could also be heard emanating from the left wheel arch, when listening with a stethoscope there's no tapping from anywhere in the engine or the fuel pump. However the exact same noise can be heard from the fuel rail once the engine is warm (it taps when cold but no so loudly).
I've heard the Fuel Pressure Regulator also acts as a pulsation damper and this could account for the tapping. Any ideas? I'm tempted to replace the FPR and see if that does it but not keen on spending unnecessarily.
Any info greatly appreciated.

Someone has released the Lesser Spotted Fuel-Pipe Tapper Gremlin into your tank and it has found its way through to the front. :err:

You could try coaxing it out with a new fuel filter and perhaps a new FPR as well and if you feel really enthusiastic, check the filter sock on the in-tank pump to make sure it hasn't collapsed.

Other than the noise, is it running ok? If so i would suspect the FPR and then it's up to you whether you live with it or renew it - double-check it isn't something more serious though. ;) :D

Thanks Dave, it's running fine except for the drumming once warm! I've been over the engine with the stethoscope and with the exception of the fuel rail it sounds like volvo's version of a sewing machine. I'll try your suggestions and see where it takes me.
Myron

You're welcome Myron, i'd try the filter first rather than the FPR although if it's high mileage it might pay to change both as a matter of course.

First because it's cheaper and second because if it has a partial blockage it might be reducing the amount of fuel through the pipes causing vapour locks which could give rise to the petrol equivalent of water hammer that you get in the plumbing at home from time to time.

Good luck with it and let me know how you get on! ;) :D

The trials and tribulations of getting stuff off of an old car! Looked like a five minute job, loosen off the banjo nut, drain the filter, undo the union, bob's your proverbial! Took a bit longer and had to destroy the old filter in the process, unfortunately no improvement re the fuel rail tapping so will have to look at replacing the pressure regulator in due course! Fuel filter had to be done anyway, looked like it hadn't been touched in years!

Silly question - the fuel rail isn't loose and physically tapping on something?

Or perhaps something nearby is making unintentional mechanical contact somewhere and the fuel pipe/rail is resonating at that particularly frequency?
Stranger things have happened! :err:

The rail is solid, did an injector service six months ago, all the fuel lines are well clipped and don't appear to be knocking, I've found a similar problem reported by jaguar owners reporting a 'helicopter' sound https://www.jaguarforums.com/forum/x...-sound-135107/
Which suggests it could be the fpr but I'll double check for other possibilities before going down that route!

Not sure if the Volvos have the same sort of fuel pressure damper as the XJ40s, not as much need for it as the Jag pump is a bit "over-specced" for the engines, particularly the 3.6/4.0 models and smaller.

As far as i'm aware, the later XJ40s used the V12 spec fuel pump, when the XJ40 was originally designed, the AJ6 engine was still in its infacny and the jag engineers didn't want the Rover V8 stuffed under the bonnet so they deliberately designed the chassis NOT to take a Vee engine - that's why the Jag V12 saloon and Daimler Double-Six survived in the old Series III bodyshell until 1992 when Jag engineers had a chance to re-engineer the chassis for it.

That's why the later cars used the V12 pump and need the pressure damper.

I might have a couple of inaccuracies in there, it's a long time since i was told that by an ex-Jag Master tech who went on to run his own Jaguar Specialist business and who knows - he may have "edited" the story for me so as to make it easier to follow.

Granted the flow/pressure may be slightly higher from your pump as it's probably the turbo model pump but wouldn't have thought it would be that different on a 3.0 to a 2.3 turbo in terms of fuel requirements.
For example on my other beasts, the Rover 827, that uses a similar spec pump to the 2.0 turbo Vitesse models whereas the 2.0 n/asp and even the 2.5 KV6 make do with lower pressure and flow pumps.

Hi Dave, I'm clutching at straws here and bow to your superior knowledge, it's weird and clearly not a common problem, when using the stethoscope there are no obvious noises from anywhere on the engine except from the fuel rail, everything else is fine, dead quiet when cold only kicks in when warm!
I will have a closer look at the lines as they go down toward the back of the car, you can only hear the noise when outside the car from the front left wheel arch and inside the car from the dash so something must be transmitting the pulses there.
All the best.
Myron

Interesting it only happens when warm Myron and only on idle when it's using the least amount of fuel. That's when the bigger majority of fuel will be sent back to the tank by the FPR which will also be running at the minimum pressure where fuel is actually used as a rule of thumb.

Have you noticed on a very light cruising throttle that it happens at all?

There's a vacuum hose from the inlet manifold that goes to the FPR, if you remove it at the FPR end and plug it, run the engine(hot idle), do you get any fuel out of the vacuum stub on the FPR and does the tapping subside/alter/disappear?