AHF: Poor Compression - Causes & Solutions

Hello,

I have a question for the community; perhaps someone has an answer.
Here are a few experiences:

My G4 AHF automatic has been starting increasingly poorly since last summer, especially...
if he stood for a long time (e.g., overnight or during a long workday at the company).
I have to really put in a lot of effort, and then he comes along like a carbureted engine.
...which isn't getting enough fuel. Also, it's emitting a bit of smoke. It also has a glow plug system.
I've checked things, replaced spark plugs, renewed oil drain lines, etc. I had...
The suspicion was that the ESP might be losing some pressure due to the RME operation, and she wanted to check it.
Now, it needs to be expanded and resealed. However, to be absolutely sure, I did the following yesterday:
Okay, first, I measured the compression - with a warm engine and a good...
Motometer compression pressure recorder. I was completely taken aback.

Cylinder 1: 23 bar - Cylinder 2: 18 bar - Cylinder 3: 17 bar - Cylinder 4: 34 bar

I repeated the entire process again, but got the same result. Then...
'There was some engine oil in cylinders 2 and 3, and then I got a reading of 26 bar on both, which I considered to be...'
worn piston rings would indicate.

Since the car has only 170,000 kilometers on the odometer, and a significant portion of that is highway mileage.
I actually thought it was a bit early for worn piston rings. Now, I had several.
Indications suggest that a faulty cylinder head gasket can also be the cause in TDI engines.
can be due to poor compression. Does anyone have experience with this issue in VAG TDI engines?
The head gasket may be leaking on the narrow areas between the cylinders.
'Has anyone ever experienced this before? The cooling system is leak-tight - I pressure-tested it cold at 0.8 bar.'
After 4 hours, the pressure had dropped to 0.7 bar, and a measurement of CO2 was taken in the cooling system.
The test result was negative. While driving, I don't think I notice anything unusual, except that I feel...
The engine seems to make a slightly rough or rumbling noise during certain accelerations at low RPMs.

Before I open the engine, I was actually wondering what your experiences have been.

These are already significant deviations from each other. What other symptoms did the car have besides the poor starting? Was there any hesitation? Poor top speed? So, there were certainly several potential candidates for a faulty head gasket, but whether the AHF is one of them, I can't say. If the car has the original 170,000 km on it, worn piston rings would be unusual, but certainly not impossible. However, if it's already pushing oil into the combustion chamber, it must be quite severe. Do you have a Technoskop to view the combustion chamber from the outside?

Well, I don't know... 34 bar seems quite high to me. The ideal pressure should be between 25 and 31 bar, and the wear limit is 19 bar. Maybe it's a problem with the measuring device; could you rule out any errors there, even if it's a specialized tool? Perhaps you could find something else to compare it to. Otherwise, the deviation is really enormous.

But you can almost rule out a blown head gasket...

Thank you for your responses.

@mullemaus:

The oil came from ME, not from the engine; it was an old trick from the gasoline engine world.
when, after injecting engine oil (using an oil can) into the combustion chamber, the compression...
ansteigt konnte man beim Benziner von defekten Kolbenringen ausgehen. Whether it's with the TDi...
works - no idea - could a leak in the cylinder head gasket also cause some kind of buildup?

@matthias TDI96:

The compression pressure recorder is definitely working correctly. I took the measurement twice.
komplett durch alle 4 Zylinder gemacht, mit dem gleichen Ergebniss. Furthermore, I have...
I also experienced the same issue with my wife's Passat AFN yesterday. The result was: somewhere between...
28 and 29 bar in all 4 cylinders - after 200,000 km (although I had the [something] at 160,000 km).
ZKD wegen eines kleinen Wasserlecks nach außen bereits erneuert. And the 170,000 kilometers.
I'm sure the parts in my Golf are genuine.


Okay, based on my gut feeling, I'm leaning more towards a two-stroke engine, because at that age, there's still no piston ring.
defekt. It could be that a ring is broken or has been damaged by carbon deposits.
Piston ring groove jammed. The fact that this supposedly happened simultaneously in two cylinders is unlikely.
very likely, especially since the engine consumes virtually no oil (0.03 liters per 1000 km).
The gas leakage from the oil filler cap is also unremarkable – no more than what's seen in the Passat.
to my wife.

I've now read the idle stabilization data again using VAG-COM, and...
'It doesn't look bad: -0.7 / -0.3 / -0.5 / +0.7 (limit according to the manual +/- 2.0). I suspect that the cylinder head gasket might be slightly leaky between cylinders 1 and 2, and more leaky between cylinders 2 and 3. When starting the cold engine (after 10 hours of standstill).'
'That could then come into effect. Once the engine is running, what happens to the exhaust?'
tausch zwischen den Zylindern durch die hohen Drücke Grenzen gesetzt. As I said, in the...
I don't expect to notice any significant effects during operation.

My question was whether anyone has experienced something similar with a TDI engine before?

Starting next weekend, my wife will be traveling by train, and I will have two cars available.
(And I can spend unlimited time in the workshop ), then I will.
'I'm going to remove the cylinder head and take a look at things. Has anyone here...'
noch eine Idee wie man die Leckrate an einem Zylinder bestimmen könnte? I thought.
Possibly adjust the pistons to a middle position and introduce a specific amount of liquid.
For example, could you measure the time it takes for petroleum to seep through? Or, before removing the cylinder head, could you remove the electrostatic discharge (ESD) components and the camshaft, and position the pistons in the middle?
Apply pressure to each cylinder individually with compressed air (while locking the crankshaft).
and use a gasoline compression pressure gauge to check the pressure in the other cylinders.
measure.

Maybe you have some other ideas? I'm really feeling like I want to completely overhaul the engine.
I actually don't have (the resources and time)!

Do you warm up your sausage?
I drove for quite some time with a PÖL/diesel mixture of 80/20 (without preheating), until one day, after a long run at full load, the compression on the first cylinder was lost. When I disassembled the engine, the piston rings were stuck and full of black deposits. The engine had 230,000 kilometers (approximately 143,000 miles) on it.
If you're taking the head off, you might as well remove the pistons and check the rings; it certainly wouldn't hurt.

He didn't mention anywhere that he was traveling by train.

One could have deduced it from the signature. I didn't pay attention to that either. But with Pöl, it could very well be the piston ring issue. We've seen similar problems with gasoline engines that are only 'lightly pushed.' Renault is a good example of that.

Okay, I've opened up the engine now.

The top compression ring on piston 1 has lost its tension.

The top rings on pistons 2 and 3 have lost their tension, and...
The lower cylinders are already showing signs of wear compared to the cylinders of the 1st and 4th pistons.

Piston 4 is in perfect condition.

However, the piston rings are still functioning perfectly.
No wear - a peculiar story! Also, the issue with the piston ring grooves.
It's flawless. Otherwise, the pistons still look like new.
All the markings on the piston crowns are still clearly visible.
The cylinder walls also appear as if the engine block has just come out of the factory.
Came from the factory - no signs of wear and the honing marks are still visible.
visible.

The cylinder head and gasket were in perfect condition, and the cylinder head bolts were tightened properly.
firmly.

I'm going to get all the parts now, and I'll put it all together next weekend.
Putting puzzles back together - at least it won't bore me!