Audi A3 1.9 TDI - Power only from 2800 RPM (Solved)

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, there's almost no power, 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 in the system. Does anyone have any idea what this could be?

Already exchanged:
+ Turbocharger - new
+ LMM-new-rebuild
+ Vacuum connection for turbocharger, new.
+ All vacuum hoses replaced.
+ Vacuum check valve - new.

I have also already pressure-tested the LLK system at 1.5 bar - no leaks!
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 anyone help me?

Is the error memory empty? Okay, I will create a log for MWB 8, 10, and 11.

How does it work? Well, you simply type "performance loss" into the search function. 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 performs 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 a weasel, the hose from the charging container may have also become detached.

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 "def. KAT" or a retrofit DPF.

Has the turbocharger also been replaced with a replica?
I assume we're talking about an AFN, right?

As you've already been advised, the very first step with VCDS would be to check the control module data (specifically modules 8, 10, and 11) while the problem is occurring, or to check them at various RPMs (from 1,500 to 4,500) at full load in 3rd gear. Log in.
THEN you think about it and start to trade, not beforehand .

The problem with cheap replacement parts is that they neither match the quality nor the specifications of the original part. Consequently, it often happens in practice that you end up introducing a new problem that wasn't there before. And before one starts looking for two or more errors simultaneously, a lot of further adjustments are made until, in the end, one has no idea what's going on and starts to question the physics .

Best regards from Munich!

DieselBär30x wrote:

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

OK, I had overlooked that. However, there is still (theoretically) a pressure loss somewhere in the rest of the pneumatic system. Example from my experience: a hardened and cracked hose between the UD pump and the buffer tank.

Quote:

As you have already been advised, the very first step with VCDS should be to log the measuring blocks 8/10/11 during the problem, or alternatively, to log them from 1,500-4,500 RPM at FULL LOAD in 3rd gear.

For VP-TDI engines, you should also log the injection timing -> measuring block 4. If the timing is off, the engine will also feel very weak.

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

I've now logged MWB 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 up to that point is lower (significantly lower below approximately 2,100 RPM) than expected, which triggers the smoke limiter, reducing the injection amount and therefore the power output."

A question: Has the vehicle been performance-enhanced? If so, via chip or MoglBox?

First, reinstall the original Mass Air Flow (MAF) sensor. Then, repeat the LOG procedure. 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. Then it's not just a few values, and it's also more precise.

LMM can be a real problem if it's not an original equipment (OE) part. This can disrupt the entire system of turbocharger boost pressure control, fuel injection quantity (smoke reduction!), and, not least, EGR to such an extent that it cannot even be properly diagnosed using diagnostic logs!

Alternatively, or before taking it to a mechanic, you could try removing the exhaust flex pipe and the catalytic converter/DPF and 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 per minute).


How about the basics? Specifically, the condition of the camshaft, valve timing, and intake system. Cat and exhaust?

The boost pressure control primarily follows the requested fuel injection amount, not the air mass. Where does the new turbocharger come from?
I'm thinking about /viewtopic.php?t=10810, specifically the topic of boost pressure buildup.
hg
Herbert.

Okay, so the camshaft is fine, the turbocharger is an original 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 pump. I have a second one here that I'll install this weekend. The problem is that when the engine is idling and you give it 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 around 3300 RPM.

Okay, I see the following in the log:

1. The engine has been chipped, because no original 1.9L VP-TDI engine has a flat torque curve 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 additional torque above 2000 rpm."

3. The mass airflow sensor doesn't seem to be clearly defective, because the maximum... The LuMa/LD ratio is around 0.45, which is within the normal range for the 1.9L engine.
However, the performance below 2500 rpm is quite weak. Possibly, the AGR valve is not closing properly (or is closing late), or the VTG is closing too much -> turn the adjustment screw further outwards.
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 I'll 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 engine?

What makes me suspicious is that the engine is sluggish 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 seems to be working now. The engine runs smoothly, idles very high, and the engine speed is 1900 RPM while driving. It's running at a 100:1 ratio now, compared to before! Thank you 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? Keyword: crankshaft pulley.
As I said, the pump doesn't adjust itself automatically.