AFN: What type of engine damage is present?

Hello fellow DIY enthusiasts,

After experiencing issues with my MSG last week, here's the next (hopefully not the last) story about my engine (AFN, year 1996):

"For about a week now, I've been hearing a noise at low engine speeds (1300-2000 RPM), and it seems to start around 1/3 throttle."
Strange noises, as if the engine were only running on three cylinders (is that even possible with a diesel?). I have the impression that you can particularly hear the explosion of one cylinder. At the same time, the engine has a jerky acceleration, and it is also very weak.
As soon as the turbocharger kicks in (around 2000 RPM), the noise is no longer as noticeable, and the vehicle drives normally, including reaching a top speed of approximately 210 km/h, according to [source]. Hey.
When the engine is idling, I can hear a noise coming from the third cylinder. When you slowly increase the engine speed without any load, I don't hear any loud knocking sounds.
A few weeks ago, I replaced the fuel injectors. The engine sounded a bit rougher afterward, which is actually normal because the combustion process is more intense.

I then opened the oil filler cap while the engine was idling, and a fairly strong airflow came out (I could smell something like exhaust), similar to a hairdryer on setting 1 or 2. Unfortunately, I don't know how it was before, but is this normal? I also removed the ventilation duct. There, only a slight airflow comes out compared to the camshaft housing.

"Yesterday, I went to ATU, and the mechanic there took the car for a test drive. He thought it might be a crack or split in the cylinder head. However, I'm surprised that I don't see any oil in the coolant." My guess is that either a piston ring is worn out or there's something wrong with the cylinder wall.

I would like to have a compression test done now. Apparently, it can only be performed with the fuel injectors removed. Isn't it about more than just the glow plugs?

What do you think about all of this?

Regards,
Ernst.

I'm only familiar with it through the spark plug connection.

Regards,

Manuel.

ErJoKri wrote:

I would like to have a compression test done now. Apparently, it can only be performed with the fuel injectors removed. But doesn't it also go beyond the glow plugs, or what?

Hello Ernst,
It should also be possible to talk about spark plug drilling.
If it's only about a statement regarding cylinderdeviations, you can also perform the test on the go -> usage tips.

I also agree about the compression test through the glow plug holes. It should definitely be simpler and faster. The question then is, of course, which tester will be used for the whole process. It might be difficult to fully trust that, given the differences.

I'll do the compression test on the mountain tomorrow, if it's not raining as heavily as it is right now. Thank you for the tip.

Here's the translation:

"One more question about the implementation: I'm thinking that it uses the compression work in each cylinder as a motor brake (similar to how it works in reverse thrust). But why does it then jerk every 3-5 seconds?" Is that the compression of each individual cylinder?

For example, in second gear at 4000 RPM, you would be traveling at approximately 80 km/h.
Rolling downhill at 0.2 km/h => 10 RPM = 0.167 revolutions per second.
During one complete cycle in a 4-cylinder engine, two compression strokes occur.
=> One rotation takes 1/0.167 seconds, which is approximately 6 seconds. => One compression cycle takes about 3 seconds.

Is that correct?

Regards,
Ernst.

Deleted as requested.

ErJoKri wrote:

Maximum speed: 210 km/h according to. Speedometer.

Hi everyone,

Do you really think that a TDI engine that's supposed to go 210 km/h has compression problems ? I'm a bit skeptical. How many kilometers does it have?

Hello,

My calculation seems correct so far: 4000 RPM x (0.2/80) = 10 RPM = 0.167 RPM.
-> Approximately 6 seconds for one revolution.
-> Approximately 3 seconds for one compression.
"Only the 0.2 km/h speed seems too slow for riding on a slope." Sure, the braking effect provided by the motor is, of course, significant.

Regarding compression: To me, it sounds like (at low RPM and medium to high load) that it's lost compression. And I noticed the strong airflow coming from the oil filler opening, which also had a slight smell of exhaust fumes.
Vmax was 210 km/h according to the speedometer, which means a real-world speed of approximately 200 km/h. Then I noticed the rattling, and it has become louder over time. Currently, I'm avoiding pushing the engine to its maximum performance. Before the chip tuning, the AFN engine could reach just under 200 km/h according to the speedometer. Hey.

I also wouldn't rule out the possibility that the turbocharger has some kind of problem. I will definitely, when I have more time, log the boost pressure and other relevant data.

I am grateful for any suggestions!

Regards,
Ernst.

Oops! I forgot something else.

LL 248,000 km

Regards,
Ernst.

hi ernst,

LL 248tkm

In my opinion, an increased pressure in the crankshaft/camshaft housing is normal regarding performance. In my father's car (V6 TDI), with a similar mileage, a blocked ventilation system led to huge plumes of blue smoke during acceleration (oil vapor was forced into the combustion chamber), to the point where we feared the engine was ruined.
It's questionable whether the knocking you described is related to that. Perhaps one of the fuel injectors is delivering too much fuel during partial load or idle, causing that ignition to be louder than the others. That would also explain why the noise disappears when the system is under full load. I would also like to investigate this further.

Greetings.
Jean.

ErJoKri wrote:

My calculation seems correct so far: 4000 RPM x (0.2/80) = 10 RPM = 0.167 RPM. -> Approximately 6 seconds for one revolution. -> Approximately 3 seconds for one compression. "Only the 0.2 km/h speed seems too slow for riding on a slope." Sure, the braking effect provided by the engine is, of course, significant.

Hi Ernst,

It's not about driving, but about coming to a stop – until the compression in the cylinder decreases to the point where the downward force of the vehicle overcomes the remaining compression and turns the engine to the next compression stroke.
Then the car comes to a stop again, until... see above.

The time it takes for each cylinder to reach a "sufficient" level of compression, and thus to progress to the next stage of the combustion cycle, serves as a benchmark for comparison between the individual cylinders.

Hello Jean,

"The issue with the injectors is certainly a possibility. The engine feels very sluggish in the lower RPM range. However, that would actually indicate that too little fuel is being injected." Only if I consider that the people behind me are keeping a respectful distance because of the cloud of smoke I'm producing, then it's probably too much, at least for one of the four cylinders.

The noise is noticeable from partial load to full load, especially at lower engine speeds. It only becomes quieter above 2000 RPM, and the noise decreases as the speed increases.

I still have the old fuel injectors. I could, of course, try installing one at a time and test-driving the car. Perhaps one of the new ES nozzles has failed.

What do you mean by "blocked vent"? Oil separator and return of the ventilation to the turbocharger?

By the way, I briefly felt the airflow coming from the oil separator on a colleague's AFN today, and it seemed a little less than usual, but not by much.

@ Ulf: Thanks, I think I understand now. I'll see if I can take the test tonight.

Regards,
Ernst.

Deleted as requested.

Hi Gustav,

diesel.gustav wrote:

Can someone please help me, just this once?

Okay, then I'll do it.

Okay, I'm ready. Please provide the German text you want me to translate.

At the very end, the "Compression Test for On-the-Go" is described. It is a comparative measurement that can only detect significant differences in compression. This test cannot detect a generally low compression ratio.

Good morning.

I tried to perform the "on-the-go" compression test this morning. It turned out to be more difficult than I thought.

1. The slope must be quite significant. To be able to test in 2nd gear, you probably need around 20-25% gradient, and we don't have that in the Dachau area (it's more hilly).
2. If the incline is less steep, you need to use a higher gear. However, the compression doesn't work perfectly, meaning the car doesn't come to a complete stop.

In the 4th gear (approximately 5%), I tried to assess the time differences between two jolts (roughly every 2 seconds). The result was that they were relatively constant. However, I don't know if I have the ability to perceive differences in the hundredth-of-a-second range. For me, the rattling sounded relatively harmonious (except for the mechanical impression: it shook me quite a bit .

This weekend, I'm going to put the car on a lift and take a closer look at the exhaust system. That clacking noise at low RPMs could possibly be due to a leak in the exhaust, which is only audible when there's a certain amount of back pressure (under partial load). For example, if the catalytic converter or a muffler were blocked, the turbocharger would have to keep its impeller blades in the "full boost" position for a long time at low RPMs in order to build up the required boost pressure. This theory is also supported by the engine's very sluggish behavior at low RPMs.

What do you think of this theory?

Regards,
Ernst.

Hi,

Try the following before removing the nozzles:

'NBF failure, engine then runs in emergency mode, but it's running.'

Open the injector lines one by one, connecting them to the ESD (Electronic Spark Discharge) system, to disable individual cylinders. (Use a cloth around the injector to avoid spills).

You might get a warning indicating which cylinder is malfunctioning. In that case, you should replace the ESD (Electrostatic Discharge) component.

Connecting rod bearings, etc.: In the case of a gasoline engine, we precisely identified which bearing was faulty. It should also work for diesel engines.
Take a long screwdriver or metal rod and, centimeter by centimeter, tap along the engine block near the noisy motor to pinpoint the location where the rattling is loudest.
As I said, I haven't had this problem with diesel engines yet – you attach one end to the engine block and the other to your ear. The vibrations are transmitted directly to the inner ear – and it works surprisingly well.

My 'AFN' (presumably referring to a specific device or system) hardly 'blows' at all.

Bertil wrote:

It is a comparative measurement that can only detect significant compression differences.

Hi Bertil,

IMO, the measurement is quite precise: I once used the wheel-crank method on a gasoline engine and noticed a clear "4-cylinder" rhythm of "different" compression.

During a subsequent routine measurement, the differences were less than 0.5 bar (absolute, relative to a pressure of 15 bar).

I think that the long "measurement time" during the downhill test makes even the smallest leaks or differences appear magnified, while they are hardly noticeable at the engine speed.