AFN TDI: Boost fluctuation causes power loss?

Hi, I haven't posted anything in a while, but since my friend can't help me anymore, I'm hoping to find some expert knowledge here on the forum.
I have a Passat 35i with the AFN 110hp TDI engine. I have a slightly larger turbocharger (I can't recall the exact model) and I'm running at 1.4 bar of boost pressure (for the last 65,000 km). It runs well, but I've noticed something: when accelerating, the boost pressure drops. For example, at 1800 rpm, when I press the accelerator, the boost pressure rises to 1.4 bar. However, at 2500 rpm, it drops back to 1-1.1 bar and then increases again at higher RPMs, around 3800-4200 rpm. So, there's no power in the mid-RPM range, which is unusual. I've blocked the EGR valve, all the hoses are tight, and the turbocharger is in good condition. The only thing I've noticed is that the EGR valve, which is connected to the intake manifold, has what I think is an overpressure release valve underneath. Oil is leaking from there (below the membrane on the intake manifold, a round hole with a ball inside). When I showed this to my VW workshop, they couldn't really tell me anything and suggested I try a different intake manifold. I'm concerned that this part is expensive and it's just for testing. I hope someone can help me.
Best regards,

moonlight wrote:

I have a Passat 35i with the AFN 110hp TDI engine. I have a slightly larger turbo (I can't recall the exact model name) and I'm running at 1.4 bar of boost (since 65,000 km). It runs great, but I've noticed something: when accelerating, the boost pressure drops. For example, at 1800 rpm, I press the accelerator and the boost pressure rises to 1.4 bar. At 2500 rpm, it drops to 1-1.1 bar and then increases again at higher RPMs, around 3800-4200 rpm. So, there's no power in the mid-RPM range, which is unusual.

Hi,

Is it just a larger charger that was installed, or has the software also been modified?

Please record the data for MWB 8 and 10 while maintaining full throttle in 4th gear (or 3rd gear if necessary) from 1300 to 4000 rpm, and then upload the resulting log file to the designated upload area.

If you don't have a VAGCOM device and the engine has been chipped with unknown software, you can forget about remote diagnostics.

Hello, thank you for taking this on. Yes, the software has been changed; it was re-flashed to a socket and the software was tuned specifically for my engine. It was done by a professional and optimized on a dynamometer until it was perfect. I can't remember exactly which software it was (it was a good acquaintance who now works abroad for a rice bowl factory), but it was about 3 years and 65,000 km ago. I don't have a VAG-COM; I only have one TDI, and it didn't seem worth it. However, I suspect a mechanical defect because the intake manifold is leaking oil from what I'm calling a 'pressure relief valve' under the membrane cover. I don't know if VW can diagnose this, but I might have a way to check it. What could it be if there's a mechanical defect? And why is oil coming from my intake manifold? Could it be that it's no longer sealing properly due to the higher boost pressure, for example, up to 1.2 bar, and leaks above that? Because, according to my boost gauge, it's loud, regardless of the gear and RPM I'm in, and the gauge only rises after 2-3 seconds to 1.4 bar in third gear, with a brief overshoot of 1.5 bar. As soon as the full boost pressure is reached, it drops back to 1.0-1.1 bar and then rises again depending on the RPM (so, if I start this process at 1800 RPM, it will be 1.4 bar at 2300 RPM, 1.0 bar at 2500-3500 RPM, and 1.4 bar again at 3500-4200 RPM). It's no longer fun .

moonlight wrote:

The software, which was specifically tuned to my engine, was installed by a professional and optimized on a dynamometer until it was perfect. I can no longer say exactly which software it was. I don't have a VAG com

.
It is quite possible that "tuning software specifically designed for the engine" can already deviate significantly from its intended parameters, even with minimal signs of wear on certain components, leading to problems like the ones you are experiencing.
Therefore, we cannot provide any assistance regarding your LD issue from a distance without log data.

"Profi"-tuning software is not necessarily a quality indicator: I have seen far too much mediocrity (to put it mildly) even from reputable tuners .

Quote:

What could it be if there's a mechanical defect? And why is oil coming out of my intake manifold?

Could it be that it's no longer sealing properly, perhaps unable to withstand the higher boost pressure, for example, up to 1.2 bar, and leaking above that? }
I'm guessing it's a worn-out O-ring between the EGR unit (-> use the search function!) and the intake manifold or the pressure hose.

This means that if I start the engine at 1800 RPM, it has 1.4 bar at 2300 RPM, 1.0 bar at 2500-3500 RPM, and then 1.4 bar again at 3500-4200 RPM. It's no longer fun.

Hello,

When it comes to customized software, it's always difficult to diagnose problems remotely without any data points. Unfortunately, Ulf is absolutely right about that.

Therefore, you can only 'post something on a whim' and hope that you'll hit the mark.

I would start with Tubo:
If the VTG adjustment is linked to the turbo, a similar behavior can be expected.

When the accelerator is fully pressed, the VTG closes to build up boost pressure. Subsequently, it opens again to prevent overboost. (Are these overboost events significantly larger than they used to be?)
If the VTG (Variable Turbine Geometry) is stuck, the overboost may become more pronounced, and the subsequent opening will be more significant. If the adjustment is sluggish or stuck, the LD (Lean Definition) will collapse until sufficient exhaust volume is available to rebuild the LD with the valve in the specified or fixed position.

Has the input VAT amount been adjusted for the 'new Turbo'?
What measurement tools were used when adjusting the LD (likely referring to a lens or optical device)?

Best regards, Jochen.

Jochen_145 wrote:

What measuring instruments were used when adjusting the LD?

Hi Jochen,

If a response comes, I'm curious to see what kind of discussion develops here. I'll hold back for now...

Okay, so the boost pressure adjustment and control were done via my boost pressure gauge and a laptop. He always had slight overboost in 3rd gear, but I think it's noticeably more now.

-Has the input tax credit (VAT) been adjusted for the 'new turbo'? Sorry, I don't mean to be rude, but what do you mean by 'input tax credit'? I'm from the naturally aspirated engine industry; that is, 8V or 16V engines without forced induction. The Passat is my family car, and since nothing has ever been done to it, I haven't really delved into TDI technology. However, I've been fascinated by TDI engines since day one, so I haven't bought a new one yet, and I've decided to drive this one for as long as possible. I think it still has a few kilometers left with 230,000 km and a very well-maintained condition. I need to finish some work now, and then I'll check the VTG and get back to you later. Can a VW dealer also read the diagnostic data? Again, sorry, but with the modifications I've made, such as 8V/16V Weber engines, etc., I leave the diagnostic cable disconnected because it never gave me anything useful when having the old engines diagnosed.
Sure, here is the translation of the text from German to English:

'mfg THT' translates to 'Best regards, THT' in English.

moonlight wrote:

Quote: Has the input VAT rate been adjusted for the "new Turbo"? Sorry, I don't mean to be rude, but what does "input VAT rate" mean??

The software map provides a base value for the turbocharger control for each engine speed and fuel injection quantity, which is used by the LD (Load Demand) control system.
If the actual value of the LD (load displacement) does not correspond to the target value based on the pre-tax value, the regulation kicks in and adjusts the actual LD value towards the target value.

For good tuning software, the pre-turbo air-fuel ratio (AFR) should generally be adjusted due to the increased maximum power output.

Hi.
I wanted to update you on what I've done so far: I removed and cleaned the turbo, cleaned all the attached components, and replaced some hoses. While disassembling, I realized why my air conditioning stopped working, and now it's cold again! I've reassembled everything, but the problem persists. I think it's a little better, at least in terms of responsiveness, but the fluctuations and the inability to reach full boost are still issues. Also, it no longer reaches its maximum speed; I used to go 220 km/h, but now it's only 200 km/h (according to the speedometer).

Then, I went to my trusted mechanic's workshop today and wanted to have the error codes read, but the master mechanic had a different opinion. He brought out the diagnostic tool, looked at the car, and said that it wouldn't work because I had disabled the EGR valve (the hose wasn't connected)?!! Then he drove the car about 5 meters, let me explain the problem again, and said it was the mass airflow sensor (MAF sensor)!! Could that be it? I've had that problem before, but then I had no power at all. He said that the MAF sensor should be replaced at the same interval as the timing belt, about 60,000 km (which makes sense for the timing belt), but the MAF sensor? I just checked, and my MAF sensor is 54,000 km old. What do you think about that? Does anyone have a 100% working MAF sensor?
Best regards,