AGR Delete: Causes & Solutions for High Boost.

Hello,

The EGR sludge can, in some vehicles, reach dimensions that almost suggest a long-term design flaw (see appendix in https://community.dieselschrauber.org/en/viewtopic.php?t=3095).).

I now suspect that the worst cases may arise from a combination of driving profile (frequent operation at low load) and excessive boost pressure at low load, where the latter (as is often the case) would likely go unnoticed or at least unheeded due to the lack of error reporting.
Because insufficient boost pressure can reduce performance and therefore needs to be corrected.
Too much "ducking" (engine braking) in the partial load range makes the engine more responsive when accelerating, which is a positive thing, but in the worst case, it can consume a little more fuel.

Therefore, I have added the following to the AGR-FA:

Quote:

The overall system is designed from a software perspective such that, based on the fuel injection volume requirement determined by the accelerator pedal, a) The boost pressure is regulated according to the characteristic curve. b) The air mass should be regulated by the EGR system according to the EGR characteristic map. In the boost pressure map, seemingly excessive pressure values are present in the partial load range, which create air reserves for sudden acceleration and thus improve the engine's responsiveness. Therefore, in the partial load range, it frequently happens that the potentially available amount of fresh air is increased by adjusting the boost pressure, and then reduced back to the target value by opening the EGR valve. Consequently (for certain engine speed and load ranges): the higher the boost pressure, the wider the EGR valve opens. Therefore, if some vehicles operate in the partial load range with slightly excessive pressure due to tolerances in the turbocharger control (adjustment of the VTG rod, etc., possibly also due to a jammed VTG!), a higher AGR (Exhaust Gas Recirculation) rate is regulated compared to vehicles with correct or insufficient boost pressure, and the deposits in the intake manifold will grow more strongly and quickly. Generally, the same can be expected when chip tuning increases the target boost pressure even in the partial load range (and the AGR map remains unchanged with regard to the emission class). This is apparently a common tactic to have more boost pressure "in reserve," which results in a more spontaneous and aggressive engine response when accelerating out of partial load.

Based on this, my conclusion is that, to prevent sludge buildup in the intake manifold , especially with a functioning EGR system , one should check the boost pressure behavior in the partial load range -> conduct extensive logging trips using diagnostic data 3 and 11. In particular, when the EGR is open (duty cycle above approximately 25%), the regulated boost pressure should not exceed the target value -> if necessary, rotate the VTG rod slightly longer or restore the VTG's functionality.

What do you think about it?
Are there any logical flaws in this, or do things actually work fundamentally differently in practice?

Hi Ulf,

ulf wrote:

Therefore, if some vehicles operate with a slightly elevated pressure in the partial load range due to tolerances in the turbocharger control (adjustment of the VTG rod, etc., possibly also due to a stuck VTG!), a higher AGR (Exhaust Gas Recirculation) rate is regulated compared to vehicles with correct or insufficient boost pressure, and the deposits in the intake manifold will grow more rapidly and intensely. It's difficult to assess whether the deposits grow more strongly or quickly with a higher EGR rate – I, at least, find it questionable. It would imply that all EU3 diesels would be more affected than EU2 diesels, and automatics would be more affected than manual transmissions. I believe it's more likely a question of the intake manifold design, the EGR introduction, and the design of the blow-by separation system, but this has already been discussed in detail here. "My EU3 ALH automatic, equipped with an AGR cooler, had approximately 3-4mm of deposits after 167,000 km, with the AGR system still functioning correctly. These deposits were mainly found on the AGR valve and at the beginning of the intake manifold. Considering the cross-sectional reduction caused by the bypass valve or AGR adjustment rod, these oil sludge and condensate deposits are almost negligible. Even after meticulously cleaning the entire intake air system, I didn't observe any changes in the measured values. However, this is likely just an isolated case." However, excessively high EGR rates at partial load can lead to increased fuel consumption, misfires, and accelerated catalytic converter degradation.

This leads me to the conclusion that, in order to prevent sludge buildup in the intake manifold

ulf wrote:

with a functioning EGR system[b], one should check the boost pressure behavior in the partial load range -> extensive logging trips with diagnostic data 3 and 11. Especially when the EGR is open (duty cycle above approximately 25%), the regulated boost pressure should not exceed the target value -> if necessary, rotate the VTG rod slightly longer or restore the VTG's functionality. The boost pressure can be above or below the target value within the control range without indicating a defect. To ensure that the measurement is only taken when the system is in a regulated state, engine speeds below 1500 RPM and fuel quantities below approximately 12mg should be excluded from the test. If the turbocharger boost pressure is increased or the throttle is adjusted, even at partial load, the EGR rate should be reduced accordingly (e.g., through adjustment). This is because, at a given actual air mass, an increase in boost pressure within a specific load point leads to a higher EGR rate in the cylinder. Best regards,

[/b]

bafische wrote:

It is difficult to assess whether the deposits grow more strongly or faster with increasing EGR rates - I, at least, find this questionable, as it would mean that all EU3 diesels would be more affected than EU2 diesels, and automatics would be more affected than manual transmissions. I think it is more a question of the intake manifold design, the EGR introduction, and the design of the blow-by separation system, but this has already been discussed in detail here.

Hi Bavarian,

That's not what I meant... but rather, if two identical TDIs with (due to tolerances) different partial load

Quote:

LDs are driven (with the same driving profile), then the car with the higher

LD will show faster growth of the AGR sludge in the intake manifold, because to achieve the target air mass, the AGR needs to be opened further.

You just presented it from a different perspective.
}If the boost pressure is increased, or the control rod is adjusted, even at partial load, then the EGR should be reduced accordingly (e.g., through adjustment), because with the same actual air mass and increasing boost pressure at a given load point, the EGR rate in the cylinder increases.} ... whereby even adapting the EGR rate can lead to a legal "grey area" (loss of operating permit?) because the exhaust values are being changed.
The "legal" solution would be to reduce the partial-load LD (load distribution) to the normal level.

ulf wrote:

That's not what I meant... but rather, if two identical TDIs with (due to tolerances) different part-load

LD values are driven (with the same driving profile), then the car with the higher :wink:LD will show faster growth of the EGR sludge in the intake manifold, because to achieve the target air mass, the EGR valve needs to be opened further.

Quote:

I understood you correctly, but I still find it questionable whether the AGR rate actually influences the amount of coolant introduced into the combustion chamber in terms of its volume/speed. As you all know, I'm not a fan of making the AGR issue even worse than it already is, and I don't want everyone to feel compelled to disable their AGR systems. Although, then people might remove their AGR valve, and I would finally be able to get a cheap replacement canister for my shut-off valve.

.... whereby even the adaptation of the AGR (Abgasgasrückführung) rate can lead to a legal "grey area" (loss of operating license?) because the exhaust values are being changed.
The "legal" solution would be to reduce the partial-load LD to the normal level.}

jaklar }