Root cause analysis, AKE engine damage

Hello.

I'm having a problem with my 2001 Allroad, 2.5 V6 TDI (AKE), with 201,000 km on the clock. The car always ran perfectly until the day it was accidentally filled with gasoline. Approximately 20 liters of gasoline were added to the existing 15 liters of diesel. The mistake was noticed, and the tank was then filled completely with diesel. The car was driven for about 400 km with this mixture. Initially, there were no problems, but then it started to stutter. Subsequently, the tank was completely emptied, the lines were flushed, and the diesel filter was replaced. The result: no improvement. Diagnosis is clear: the VP44 pump is faulty, and gasoline is not good for it.
So, I replaced the pump, but while I was doing that, a customer pointed out that the valve cover gasket on the driver's side is leaking.
Okay, let's get started right away, it seems like a good idea. Remove the cover, preferably put it back on right away. The camshafts are nicely broken in. I consulted with the customer, and the new parts from Audi are too expensive for him, so he's getting something himself from eBay. I had him sign a document stating that non-original parts are being used, and therefore no warranty applies. Everything was finished, and the vehicle ran wonderfully for 1000 km. After 1000 km, the engine started refusing to accelerate above 3000 rpm. I then started analyzing the idle speed control and everything else. Initially, there were no abnormalities, but suddenly, from one day to the next, the idle speed control showed anomalies on cylinder 6, with a value going up to +2.8 mg/H. Compression measured, result:

- Cylinder 1: 23 bar
- Cylinder 2: 22 bar
- Cylinder 3: 23 bar
- Cylinder 4: 22 bar
- Cylinder 5: 21 bar
- Cylinder 6: 15 bar

Valve cover off, the camshafts and lifters were completely clogged again. Two lifters had fallen out. The hydraulic lifters were almost all very soft. Both cylinder heads were removed for troubleshooting. Diagnosis: Piston in cylinder 2 was cracked, which was surprising since there were no apparent issues. The cylinder heads were cracked in all cylinders, from the exhaust valve to the glow plug bore. The valves were relatively tight, for example, cylinder 4 had less leakage than cylinder 6, where the compression was missing. It appears that nothing is getting into the cracks. Clear spray patterns are visible on all cylinders except for cylinder 1.
Due to the many defective cars available, a used A6 with a transmission problem was quickly purchased for a low price. However, I'm now concerned about the spray pattern on the pistons; it doesn't seem normal. According to the previous owner, the car hasn't been modified or tuned in any way. I haven't been able to find any obvious flaws or defects so far.
I don't want the new engine to look the same way after just six months. Therefore, my questions are:

-Is the pattern of markings on the pistons normal?
-Are the cracks in the head normal? (e.g., Golf II TD, it's normal, right?)

The injectors were tested and all achieved 220 bar pressure with a good spray pattern.

Bad story, but unfortunately true.


Piston cylinder 1:
[img][/img]

Piston cylinder 2:
[img][/img]

Piston cylinder 3:
[img][/img]

Piston cylinder 4:
[img][/img]

Piston cylinder 5:
[img][/img]

Piston cylinder 6:
[img][/img]


Piston skirt damage.
[img][/img]

[img][/img]


Cracks in the head:
[img][/img]http://www.pictureupload.de/originals/59546/221209105147_sonstige_kolben_zylinder_1.jpg{MARKER}http://www.pictureupload.de/originals/59546/221209105151_sonstige_kolben_zylinder_2.jpg{MARKER}http://www.pictureupload.de/originals/59546/221209105151_sonstige_kolben_zylinder_3.jpg{MARKER}http://www.pictureupload.de/originals/59546/221209105151_sonstige_kolben_zylinder_4.jpg{MARKER}http://www.pictureupload.de/originals/59546/221209105152_sonstige_kolben_zylinder_5.jpg{MARKER}http://www.pictureupload.de/originals/59546/221209105152_sonstige_kolben_zylinder_6.jpg{MARKER}http://www.pictureupload.de/originals/59546/221209105152_sonstige_kolben_gerissen_1.jpg{MARKER}http://www.pictureupload.de/originals/59546/221209105152_sonstige_kolben_gerissen_2.jpg{MARKER}http://www.pictureupload.de/originals/59546/221209105152_sonstige_kopf_gerissen.jpg{MARKER}

Spritzbild defective, not in order. I once had a similar issue with an AHU, and the nozzle was spraying directly onto the piston without atomizing.

Crack in the cylinder head: As you can see from the piston, the heated material has bulged upwards and hit the valve. This bent the valve and made it leak. The hot combustion gases flowing through heat the valve seat ring, causing it to expand, and the aluminum essentially bursts. In the 1.9 engines, the distance between the bridge and the nozzle holes is too small, which is why the crack occurred in that area. The glow plug inlet is located closer to the surface, or the material is weaker, in the case of the 2.5V6.

Remove the valve and inspect its sealing surface. You will probably notice that this one isn't fully exposed.


New engine, new nozzles, and that's it .

vwSchrauber wrote:

The spray pattern is defective and not in order. I once had a similar issue with an AHU, and the nozzle was spraying directly onto the piston without atomizing. Crack in the cylinder head: As you can see from the piston, the heated material has bulged upwards and hit the valve. This bent the valve and made it leak. The hot combustion gases flowing through heat the valve seat ring, causing it to expand, and the aluminum essentially bursts. In the 1.9 engines, the distance between the bridge and the nozzle holes is too small, which is why the crack occurred in that area. The glow plug inlet is located closer to the surface, or the material is weaker, in the case of the 2.5V6. Remove the valve and inspect its sealing surface. You will probably notice that this one isn't fully exposed. New engine, new nozzles, and that's it

.
Yes, that's all correct. However, the broken piston is in cylinder 2, while the cylinder with the missing compression is cylinder 6. On cylinder 2, everything was actually okay.

The nozzles are sealed, and the top is ready for operation. I even think they might not be the best anymore; they're almost *too* good.

The spray pattern looks like the one I've seen in photos of my own and other V6 TDI engines.
I suspect the valve-piston collision is more likely due to a blockage caused by the popped-out rocker arms.
Soft hydrometers indicate a low air content, but unfortunately, this air is unevenly distributed. Otherwise, the MSG (presumably a control system) would correct it. Where there is very little air, the combustion process could extend far into the working stroke. This, in turn, leads to overheating. You can't expect much in terms of compression pressure if the cylinder isn't properly filled.
I would largely disassemble the engine, definitely remove the oil pans, and verschandeln them of any debris. The oil pump should be carefully inspected or replaced.
Take a look at motorenprofis.de; they specialize in cases like that.

christians wrote:

I would largely disassemble the engine, definitely remove the oil pans, and verschandeln them of any debris. The oil pump should be carefully inspected or replaced.

The engine is no longer being used, and a replacement is already here. I just want to determine whether the engine failed on its own, or if something in the surrounding environment (e.g., the engine control unit) caused it to fail. Because if the problem lies in the environment, the new engine won't last long either if the underlying issue isn't resolved.

Here's some news from the front lines. I just disassembled the cylinder head, and the angular offset of the compression rings was very noticeable. Here are the details:

- Cylinder 1: approximately 140°
-Cylinder 2: approximately 20° (this is not a typo ).
- Cylinder 3: approximately 160°
-Cylinder 4: approximately 170°
-Cylinder 5: approximately 175°
-Cylinder 6: approximately 90 degrees.

What do you think about it? That doesn't just happen on its own, does it?

I agree with ChristianS regarding the valve contact issue.
The cracks are likely normal occurrences for lead-footed drivers.
The reason the old cylinder heads were prone to cracking was likely the reason why the cylinder head cooling system was improved by switching to roller rocker arms, which enhanced ESD (Electrostatic Discharge) performance.

So, everything should be okay in the surrounding environment, right?

Perhaps it would be worth checking whether the desired injection timing is achieved at full throttle and high engine speeds.
The shadows cast by the fuel injectors on the pistons look normal to me.

For a car with only 180 horsepower and 200,000 kilometers, a piston failure seems to happen far too early. Either the driving profile is very unusual, or it's a combination of "Box" mode (likely referring to a driving mode) and constant full throttle, or it's simply bad luck, or the odometer reading is incorrect.

Were complete new cylinder heads installed via eBay, or just new valve covers, or a whole new engine? Because if the waves had been okay, they could hardly have traveled a significant distance in just 1000 km.

Best regards, Rainer.

Rainer K. wrote:

Were complete heads installed via the Ebucht, only new manifolds, or a whole new engine?

A new camshaft set, including all 4 camshafts, 24 lifters, 24 pushrods, and 24 valve retainers. According to the customer, it cost 699€, which suggests it probably isn't a very good product for that price.

"The mileage is 100% accurate. The current owner purchased the vehicle new from the dealership. The service history is complete, with all maintenance performed by Audi until the end. I think those "good" parts from eBay probably ruined everything." Well, I already told him that back then, but he didn't want to listen.

Here's some information for those who want to do a conversion: The AKE (presumably an engine component) from a vehicle with an automatic transmission does not fit into a vehicle with a manual transmission. The crankshaft needs to be replaced, and then it will work. I specifically inquired with Audi beforehand to see if there were any differences. According to Audi, there is only one type of crankshaft, regardless of whether it's for a manual or automatic transmission. I assume that at some point, they agreed on a "universal" crankshaft. Or perhaps they only offer the crankshaft for the manual transmission now. Because the switch is in automatic mode, an intermediate shim should work.

Could the piston crack have anything to do with the gasoline being added? As I understand it, this part was driven for approximately 400 km using a 50:50 mixture. That must generate a tremendous amount of heat when that much gasoline is burned, right?

mserge wrote:

Could the piston damage have anything to do with the gasoline being added? As I understand it, this part was driven for approximately 400 km using a 50:50 mixture, and that creates a tremendous amount of heat when that much gasoline is burned...right?

Not 50:50. There were approximately 15 liters of diesel left in the tank, and then 20 liters of gasoline were added. The mistake was then noticed, and the tank was filled with diesel. Something like an 80:20 ratio.