Clacking Engine: Volvo V70 & Audi 2.5 AEL Repair

Hello.

Perhaps someone can help me with the diagnosis.
Volvo V70 TDI with the older Audi 2.5 (AEL) TDI engine, 295,000 km.
Long distance driving. No measurable oil consumption. Diesel: 5.5 to 6.3 liters per 100 km. Excellent performance.
and driving characteristics.

'For approximately 50,000 kilometers, there has been a faint clicking noise, noticeable in both cold and warm conditions, only audible under load, and most easily detected between 1800 and 2800 RPM.'
When you release the gas pedal, it immediately stops, and you can't hear it even when idling.
Sometimes it's impossible to determine, (outside temperature??)

However, there has been a significant increase recently, and now there's also a faint clicking sound during operation.
and it is also clearly audible in the LL (low-latency) setting.

The screwdriver test didn't help me much. I got some advice from a friend who knows about these things.
'There's a knocking sound coming from the plunger of the vacuum pump. Apparently, it's a common problem with this machine. But shouldn't it only occur under load?'

The master technician at Volvo suspected the shock absorber (about 8 weeks ago, when it was much quieter).

If it were a hydro lock, shouldn't it be audible specifically after starting the engine?

'Somehow, I think it's more likely to be a piston issue or a problem with the nozzle...'

It's been extremely loud since today, and it sounds really bad. I'm almost afraid to accelerate anymore.

Can anyone offer suggestions for further diagnosis?

Thank you, Thomas.

Quote:

If it were a hydro, shouldn't it also be audible specifically after starting?

Actually, yes, but not necessarily. How is the oil level? Are the filter and oil new?

Quote:

Somehow, I think it's more likely to be a piston pump issue or a nozzle problem... Since today, it's extremely loud, and it sounds really bad. I'm almost afraid to accelerate anymore.

First, you should try to determine where the noise is coming from (the head or the block).

Then I would disable each cylinder one by one, in sequence, to see if the noise disappears. To disable a cylinder, you disconnect the corresponding fuel injection line from the injector and use a hose to divert the diesel into a container.

If the noise disappears when one of the cylinders is deactivated, you can rule out the camshaft and high-pressure pump; instead, the problem likely lies with a piston slap, bearing damage in the connecting rod or connecting rod bore, or within the injector itself.

thrurl wrote:

..... A special drink from a friend's circle. "There's a knock coming from the plunger of the vacuum pump. Apparently, it's a common problem with this machine. But shouldn't it only occur under load?" Thank you, Thomas

.
You can rule out the vacuum pump plunger by repeatedly pressing the brake pedal when you hear the clicking sound. If the plunger is stuck, it will stop clicking – even if it was making noise before.
Okay, so a knocking sound when accelerating = the cause is likely the plunger of the fuel injection pump.
I believe that the other causes mentioned are more likely.

Hello.

Thank you for your responses. It appears that the plunger of the vacuum pump is failing.
Braking while the noise is occurring definitely won't make a difference.

We just tried to get a better idea of what's going on using a stethoscope, but the results weren't clear.
except that it seems to be coming from the side with the auxiliary equipment.

Now that the noise is much louder, I went back to Volvo, and they are now supposedly very certain that it's the aforementioned vibration damper.

If that's not the issue, I will proceed with investigating the cylinder deactivation system using the fuel injector control.
As suggested.

Okay, and thank you again for the information.

Best regards, Thomas.

I'm also leaning towards the vibration damper, assuming that's the part where the V-belt is driven. A friend of mine had a really bad experience with it; it looked like the engine was about to explode. All the rubber had disintegrated, and the part was broken into two pieces hanging off. You have to replace the entire disc (which cost around 250 euros back then).

Let the engine idle and watch the pulley; if it wobbles even slightly when an assistant gives it some gas, then you've found the problem.

Good luck!

Hello.

The vibration damper was likely significantly worn. With the new part, the noise has now disappeared at idle, but it is still present under load.

I temporarily disconnected the vacuum pump as a precaution, but there was definitely no change; it can therefore be ruled out as the cause.


I followed your suggestion and removed each fuel injector one by one, then briefly started the engine. With a 4-cylinder engine, the noise is roughly the same in each case. However, it's difficult to judge now because with each cylinder removed, one cylinder is missing, and the engine runs unevenly.

However, with the cylinder that had the needle valve injector, the noise was definitely gone, and the machine ran much more smoothly when briefly revved up.

Could this possibly be due to an emergency program being triggered as a result of a missing signal?
from the needle lift injector? Or do you see that as a clear indication of a problem with this injector?
or this cylinder? It could also be the relevant piston or connecting rod bearing that is now...
due to low demand.


Thank you for all the tips, Thomas.

Quote:

Could this not be due to an emergency program triggered by a missing signal? from the needle lift injector? Or do you see that as a clear indication of a problem with this nozzle? or this cylinder? It could also be the relevant piston or connecting rod bearing that is now... due to a lack of load, it is...

When the needle lift sensor fails, the injection timing is determined based on fixed values from a lookup table because a comparison between desired and actual values can no longer be performed. Additionally, the amount of fuel injected is reduced. I believe that these pre-programmed values should have little influence on the noise produced during testing.

You could temporarily swap the injector with a needle valve actuator from one cylinder with an injector from another cylinder (leaving the electrical connection disconnected). This will help you determine if the problem is moving or not.