You may be on the right track with your theory that the fuel rail is not holding pressure overnight. But you could also have the same problems with, say, glow-plugs that are not working efficiently (or at all). In that case, the vehicle will be hard to start form cold and could easily display the other symptoms you’re seeing.

Modern turbo-diesels have a pretty complex (and super high-pressure) fuel system, so there’s plenty to go wrong. A check-up at a diesel specialist is probably the best advice. Don’t be tempted to tackle the problem in your driveway, either, as these systems run at sufficient pressure to remove fingers if you get it wrong.

In fact, a diesel engineer once told me that one of the big concerns with these modern diesel engines is making them tamper-proof to protect inquisitive backyard mechanics.

There are plenty of reasons why a diesel won’t start in the morning. This can often be traced back to a problem with the fuel system or the glow-plugs which are needed to warm the combustion chambers before the diesel will ignite.

As for the noise, it pays to remember that diesel engines are inherently noisy, but if you’ve owned the car for a while and are familiar with its normal level of racket, then any new or louder noises signal a problem. If, indeed, the new noises are connected to the engine’s refusal to start easily, you might be looking at an engine with worn out internals. At that point, it’s time to recondition or replace the original engine.

But before you do any of that, have a diesel specialist look at and listen to your engine running, and you might find the problem is a simple one after all.

It all depends on the model and variant of the vehicle you’re talking about, but, generally speaking, the fuel rail pressure sensor on a turbo-diesel engine will be somewhere along the fuel rail. But, even if you know for absolutely certain that this sensor is the problem, we have to advise against any amateur mechanic taking on this, or any other, job that deals with the fuel system. That’s because the fuel systems on a common-rail turbo-diesel run at incredibly high pressures. So they’re dangerous things to fiddle with.

In some cases, the pressure could be enough to slice fingers off. Which means you have to know the exact process to follow in order to bleed off any residual pressure in the fuel system (even if the engine hasn’t run for days) before you can safely tackle jobs like this one. Leave it to the experts, in other words. Also, a specialist is a chance to be able to make a more accurate diagnosis than the one given by an online forum of dubious credibility.