AFN Engine Problems: No Improvement with Boost

99 AFN is increasingly experiencing soot emissions.

Hello everyone,

My car is increasingly producing black smoke (soot) when I accelerate fully. (Specifically, only when accelerating hard above approximately 2500 RPM - this wasn't the case before!)

Operating conditions (unchanged for approximately 80,000 km):

Engine chipped, boost pressure 1.3 bar (No improvement with higher boost pressure!).
Nozzles, mileage 100,000 km, removed and inspected approximately 20,000 km ago.
Mass airflow sensor clamped to maximum value using a bypass circuit. (This has no effect on soot emissions as long as the boost pressure is correct.)
Block 220TKM, Head 40TKM.
AGR deactivated. Compression is good, oil consumption has been minimal since the head was replaced.
VAG COM reports everything is OK, and the injection timing also appears to be correct according to the timing checker.


The engine doesn't have the power it used to, but the fuel consumption hasn't increased significantly. In short, the power is decreasing, the fuel consumption isn't increasing much, but it produces a lot of black smoke when running at full throttle.

I can't figure out what's gradually getting worse and causing this effect.

Kann Verschleiß der ESP das bewirken ? How?
The nozzles have only been used for 100 kilometers.
In the partial load range, up to approximately 80% load, no issues are apparent.
Does anyone else experience similar problems?

Quote:

VAG COM says everything is OK, and the injection timing is also correct according to the timing checker.

The Timing Checker is only responsible for the static start.

What about dynamic control?
What does the Block 004 target-actual comparison show under different load scenarios (excluding thrust cutoff)?

m;

Engine chipped, boost pressure 1.3 bar (No improvement with higher boost pressure!).
Nozzles, mileage 100,000 km, removed and inspected approximately 20,000 km ago.
Mass airflow sensor clamped to maximum value using a bypass circuit. (This has no effect on soot emissions as long as the boost pressure is correct.)


The engine no longer has the power it once had.

Hello,

How much horsepower are you running?
1.3 bar is already quite a high pressure for an AHF (Abgas-Heckfilter). Even if you crank up the pump voltage to its maximum, you should still have a lambda value well above 1.2 at 1.3 bar, which means you should be running relatively cleanly.

Perhaps the AGR valve is not closing completely, resulting in the boost pressure being composed of exhaust gas pressure and fresh air pressure. In this case, the turbocharger would need to be controlled less aggressively, as it doesn't have as much work to do to reach the desired pressure.

Maybe you should connect the LLM again and see if the 'boost pressure' is consistent with the amount of fuel being injected.

Best regards, Jochen.

Hello,

"There are people who run the AHF (presumably a type of engine or system) with a holding pressure of 1.35 bar... With standard-sized injectors, I wouldn't expect any soot, even at 1.30 bar."
Here's the translation:

"Check if the plastic air duct has rubbed against the intercooler; if it has, all the air will be blocked. Otherwise, generally check the tightness of the intercooler system and see what the EGR valve is doing; it's easy to remove on an AHF engine."

Best regards, Rainer.

Rainer K. wrote:

Here's the translation: "Check if the plastic air duct has rubbed against the intercooler; if so, all the air will be lost. Otherwise, generally check the tightness of the intercooler system and see what the EGR valve is doing; it's easy to remove on an AHF engine."

I completely agree. The problematic aspect in this context is that you've overridden the Mass Air Flow sensor (MAF). Normally, the engine would enter a limp-home mode if the boost pressure values deviate from those measured by the MAF for an extended period. However, in your case, this safety function is disabled. There's a risk of turbocharger damage!
The AGR valve is also a likely culprit. In many cases, especially with Russian-made vehicles, the main cause of this issue is a leak in the AGR valve and insufficient boost pressure. If fresh air leaks through the AGR valve, the functioning mass airflow sensor (MAF) receives the information that there is enough oxygen to inject large amounts of fuel, which is not the case.

Hello, and thank you for all the responses. I've been searching for a while now, as the problem has been gradually getting worse.

@ Dieselmartin

The target/actual comparison is correct. My pump is set to advance the timing slightly because it allows for faster adjustment of the timing advance during acceleration.

@ Jochen

My pump and injectors are original equipment, and they probably used to produce around 150 horsepower, but certainly not anymore. However, even now, the engine still produces significantly more power than the original factory specifications.
Boost pressure: Previously, I was able to run with 1.0-1.2 bar, but I increased it again because of the misfire.

The mass airflow sensor (MAF) isn't helping here because the indicated air mass at full throttle is no longer accurate. The effect is that when you increase the boost pressure further, the airflow velocity within the MAF exceeds its specifications, causing the MAF readings to suddenly drop. This, in turn, causes the engine control unit (ECU) to reduce the fuel injection amount. My MAF sensor is currently in the storage room.


'The AGR valve has been disconnected for 100,000 km after I cleaned out large amounts of oil/carbon deposits from the intake manifold (see my forum post from that time).'
Since then, it hasn't moved. But I'll probably take it off just to be safe, sometime this weekend.

The engine is a A F N!

@ Rainer, I've had a new intercooler hose (turbo to intercooler) for 3 weeks. The old one failed, and the ECU went into limp mode. I checked the entire air intake system in the process. It's a completely different and very clear error.

It can't be the intercooler system, because I can easily and consistently achieve a boost pressure of 1.5 bar.

@ Tagessuppe: My engine control unit (ECU) doesn't show a relationship between boost pressure and lambda (air-fuel ratio) values that would trigger a limp-home mode. However, there is a safety function that initiates limp-home mode if the set boost pressure is not reached within approximately 2 seconds, even with full throttle.


Regarding the AGR (Abgas Rückführung - exhaust gas recirculation) system: It is typically open in the partial load range, and then when the exhaust pressure is higher than the boost pressure. At full throttle with 1.3 bar of boost pressure, what is the exhaust pressure? The pressure does not necessarily have to be higher, because the turbocharger is driven by the mass flow of exhaust gases, not by pressure.
In other words: A large mass of exhaust gas, moving at high speed, generates enough driving force even at lower pressure to compress a smaller mass of intake air to a higher degree.

And if the pressure in the exhaust isn't higher, then no exhaust gases can enter the intake manifold. But as I said, I haven't been able to measure that yet. However, I'm going to remove the EGR valve and permanently block it.

Fresh gas entering the EGR valve => I can rule out the exhaust system due to the achievable boost pressures.

Here's another piece of information. For the TÜV (German technical inspection), I drastically reduce the maximum fuel injection amount to approximately 80 horsepower, while keeping the boost pressure values the same. This results in my AFN engine being certified with 'new car' values, which means there's a full-load problem! But what is it?

However, there's a good side to this – if someone tailgates you with a 50cm gap, all you have to do is floor the accelerator, and they'll create some distance.

The mass airflow sensor (MAF) is not helping here because the displayed air mass at full throttle is no longer accurate. The effect is that when you increase the boost pressure further, the flow velocity in the MAF exceeds its specifications, and the MAF values suddenly decrease, causing the ECU to reduce the fuel injection amount. My MAF sensor is in the storage shelf in the basement.

Hello Garth,

Hmm, that would be new to me, that this effect occurs already at a pressure of 1.3 bar.
There are enough instances of people running standard LLMs at pressures exceeding 1.4 bar without encountering smoke issues.

I'm happy to be corrected if I'm wrong, but I believe these voting systems are all fundamentally flawed. If I remember correctly, Rainer doesn't change the lambda sensor (LMM) in his motorsport kits, including the turbocharger.

One more piece of information. For the TÜV inspection, I drastically reduce the maximum fuel injection amount to approximately 80 horsepower, while keeping the boost pressure values unchanged. (..), meaning there's a full-load problem! But which one?

What does your fuel consumption say? Has it increased?
Could it be that the pump is always injecting too much fuel? Even if, at the maximum setting, it shouldn't really be producing excessive smoke (as mentioned above).

What does your VTG control system indicate? Could it be that the LD sensor is faulty and displaying incorrect values? In that case, the turbo wouldn't actually be delivering 1.3 bar, even though the sensor is showing that. Your software, as I currently understand it, wouldn't detect this.
Then you're always applying too much, because you don't have access to the actual LM (likely referring to a measurement or value).

Best regards, Jochen.

Hello Jochen,

I only had my own mass airflow sensor (MAF) to measure with, and it was new. The effect of the decreasing measured airflow with increasing flow rate was clearly measurable and reproducible.
(Back then, I electronically capped the mass airflow sensor (MAF) at its maximum value because the boost pressure was above 0.8 bar.)

If that's not the case for others, I wonder why.

@ Rainer: Can you confirm that this effect is unknown?

If that's not normally the case, then the new mass airflow sensor he installed back then was probably already faulty.

LDA is a mechanical pressure gauge. When I turn off the boost pressure increase, the LDA reads approximately 0.9 bar. (However, at that point, it produces a lot of black smoke...)

I installed the AGR system over the weekend, but that's not the issue. I can't really say much about fuel consumption, but it hasn't increased significantly. I'm getting around 7-7.5 liters per 100km, while my wife gets about a liter less. Of the increased fuel consumption compared to the standard models with manual transmissions, approximately 1 liter is due to the older AG4 (01N) automatic transmission, and about 0.5 liters is due to the 225 tires.
'What surprised me negatively was how much it was, but I tried it again by temporarily switching back to 195s, and that worked out.'

Hello,

Even though I mentioned above that it wasn't the AGR valve because it seemed to be sealing properly when the engine was off, it was definitely the AGR valve.

The exhaust pressure pushes the EGR valve open, and as the exhaust pressure decreases, the valve closes again.

A piece of sheet metal placed between the EGR valve and the intake manifold permanently solves the problem.

garth.brooks wrote:

The exhaust pressure pushes the EGR valve open, which also closes cleanly again when the exhaust pressure decreases. A piece of metal placed between the AGR (Exhaust Gas Recirculation) and the intake manifold permanently solves the problem.

Ah yes: it's interesting to read a case like this with concrete data .