Audi A3 TDI: Low Power, Fix at 2800 RPM

Hello, I'm having a problem with my Audi A3 1.9 TDI, 110 hp, 1998, with electric windows!

The car doesn't really start pulling until around 2800 RPM; below that, it's completely useless, and it performs worse than a naturally aspirated diesel engine. Even when idling, if I floor the accelerator, it takes a very long time to reach 3500 RPM. There are no error codes stored. Does anyone have any idea what could be causing this?

Already exchanged:
+ New turbocharger.
+ LMM-new-rebuild
+ Vacuum line for turbocharger, new.
+ all vacuum hoses - new.
+ Check valve for vacuum applications - new.

I also tested the LLK system and it held pressure at 1.5 bar without any leakage!
I checked measurement block 1 using VCDS, and the fuel injection quantity at idle is 4.8-5 mg. The fuel pump's injection timing has already been checked by VW, and a different control unit has also been tried – but the problem persists.

Can someone help me out?

Is the fault memory clear? First, create a log of modules 8, 10, and 11.

Wie das funktioniert? Nun, gibst du "Leistungsverlust" in die Suchfunktion ein. Then read...

PS: If the original Mass Air Flow (MAF) sensor is a Bosch part, experience shows that using an aftermarket replacement will likely fail in 90% or more of cases.

mani38 wrote:

A3 1.9 TDI, 110 HP, year 1998, VEP! The car doesn't start pulling until around 2800 RPM; below that, there's nothing, and it runs worse than a naturally aspirated diesel engine

. The classic cause for this is usually a rodent bite in a vacuum hose, for example, the one leading to the turbocharger control valve (VTG): Due to the vacuum leak, the VTG cannot close properly, and therefore boost pressure only occurs at high RPMs.
Without martens, the hose from the charging socket may also have come loose.

Hello everyone!

@Ulf:

mani38 wrote:

... + all vacuum hoses - new ...

If we're already engaging in this lighthearted game of fortune-telling, I'm in favor of either a definite CAT (Catalytic Converter) or a retrofit DPF (Diesel Particulate Filter) .

Has the turbocharger also been replaced with a replica?
I assume it's about an AFN, right?

Wie Dir schon geraten wurde, wäre der aller erste Schritt mit VCDS mal die MWB 8/10/11 während des Problems bzw. mal von 1.500-4.500 U/min bei VOLLLAST im 3. Glogging in.
THEN you think about it and start to trade, not beforehand .

The problem with such cheap replacement parts is that they neither match the original part in quality nor in specifications. Consequently, it often happens in practice that you inadvertently introduce a new fault with such parts, which wasn't there before. And before you start looking for two or more faults at the same time, you diligently keep replacing parts until you eventually have no idea what's going on and start questioning the laws of physics .

Best regards from Munich!

DieselBär30x wrote:

mani38 wrote: ... + all vacuum hoses replaced...

OK, I had overlooked that. However, there is still (theoretically) a vacuum leak somewhere in the rest of the pneumatic system. For example, from my experience: a hardened and cracked hose between the vacuum pump and the pressure regulator.

Quote:

As you have already been advised, the very first step with VCDS would be to log the measuring blocks 8/10/11 using the software, while the problem is occurring, or alternatively, to log them from 1,500-4,500 RPM at FULL THROTTLE in 3rd gear.

For a VP-TDI, you should also log the injection timing -> measuring block 4. If the injection timing is late, the engine will also feel quite sluggish.

Hello, thank you for the quick responses. It's a motor code: AHF!

I've now logged MWB entries 8.10 and 11!

Hi Mani!

The LOG looks like this:
The target boost pressure is not reached until approximately 2,500 RPM. The air mass flow rate is lower than expected up to that point (and significantly lower below approximately 2,100 RPM), which triggers the smoke reduction system, reducing the fuel injection amount and, consequently, the power output.

Here's a question: Has the vehicle had its performance enhanced? If so, was it done with a chip tuning or a MoglBox?

First, reinstall the original Mass Air Flow (MAF) sensor. Then, repeat the LOG process. It's better to do this on a quiet, straight road. Start with full throttle in 4th gear, just above the low-load RPM, and accelerate to just below the redline. This will give you not only a few more data points, but also more accurate readings.

"The LMM (Mass Air Flow Sensor) can really be a problem if it's not an original equipment (OE) part. It can disrupt the entire system, affecting turbocharger boost control, fuel injection (which can lead to excessive smoke!), and even the EGR system, to such an extent that it's difficult to diagnose properly, even with a diagnostic log."

You could try removing the exhaust flex pipe and/or the catalytic converter/DPF, either as an alternative or before other checks, and then see if the problem persists or if you suddenly experience more power at low RPMs.
Then at least it would be taken care of right away.

Best regards from Munich!

If you look at the graph of air mass, you'll see that it increases much more gradually between 1869 and 2016 (in units of revolutions per minute).


How about the basics? What's the condition of the camshaft, valve timing, intake and exhaust system (including catalytic converter and exhaust)?

The boost pressure control primarily relies on the requested fuel injection amount, not the air mass. Where does the new turbocharger come from?
I am thinking about https://community.dieselschrauber.org/en/viewtopic.php?t=10810, specifically the topic of boost pressure build-up.
hg
Herbert.

Okay, so the camshaft is fine, the turbocharger is a genuine VW part and is new, the catalytic converter will be removed this weekend, I need to try the old, original mass airflow sensor again, and I've now checked the fuel pump - the fuel injection timing is too early: 92° and it's already running almost outside the measurement range, so I can barely see the yellow line in the TDI timing checker, it's right at the top of the screen!
I think the problem is with the fuel pump. I have a second one here that I'll install this weekend. The issue is also that when the engine is idling at full throttle, it takes a very long time to rev up, as if it's being held back. It only starts to rev up normally or faster from around 3300 RPM.

Okay, I see the following in the log:

1. The engine has been modified (chipped), because no original equipment manufacturer (OEM) 1.9L VP-TDI engine has a flat torque curve limited from 2200 to 3900 rpm.

"The torque and opacity values are equal from 2000 rpm onwards. Therefore, increasing boost pressure or air mass would not generate any additional torque above 2000 rpm."

3. The LMM (likely referring to a measurement or sensor) doesn't seem to be clearly defective, because the maximum air mass/load ratio is around 0.45, which is within the normal range for the 1.9-liter engines.
However, the performance below 2500 rpm is quite unstable. Possibly, the EGR valve is not closing properly (or is closing late), or the VTG is closing too much -> adjust the limiting screw by turning it further out.
EDIT:
Alternatively, disconnect the VTG hose from the turbocharger and check that the VTG lever is in the open position. If the engine revs up more quickly at low speeds without any load, it's clearly due to the VTG closing too much.

"Thanks, I'll double-check that again in the next few days and get back to you."

mani38 wrote:

So, I can barely see the yellow line in the TDI timing checker anymore; it's right at the top of the screen!

Did you choose the correct motor?

What's concerning me is that the engine is sluggish in its revving, even when idling.
If I'm thinking correctly, there probably isn't much boost pressure here anyway, so it's worth checking the mass airflow sensor (MAF) and injection timing, as well as the EGR valve, to make sure it's not stuck open.

Yes, I chose the right engine. Thank you anyway!
Okay, so I adjusted the fuel pump and it turns out it's running smoothly now. It idles really well and the engine speed is 1900 RPM while driving, which is a huge improvement compared to before! It's now running at a ratio of 100:1, which is fantastic. Thanks again for the quick responses!

How can the start of the injection be adjusted?
Skipped a tooth or are the screws on the impeller not tightened?

Did you also check the valve timing? The crankshaft pulley is a key component.
As I said, the pump doesn't adjust itself automatically.