TDI 1.9: Strange Power Loss - Troubleshooting

Hello everyone,


In the newsgroup d.e.f.a., I received the recommendation to turn to this forum with my problem.

I drive a Seat Toledo TDI from May 2001 with a 110 horsepower TDI engine, but it doesn't have a pump-injector system.

'For a few weeks now, I've been experiencing some strange problems, the connection and cause of which I can't explain. I haven't found any posts in this forum about a similar performance loss. In particular, the issue with the cruise control (see below) doesn't seem to fit the pattern.'

When consulting a workshop (especially the local, overpriced Seat partner in Wuppertal, who has already raised my suspicions with their partially outrageous estimates of working hours), I fear that they will randomly and expensively replace parts of the engine control and sensor systems based on mere suspicion.

Therefore, in this post, I am asking for recommendations for workshops in the Wuppertal, Düsseldorf, and Ruhr area that you have found to be affordable and competent in dealing with complex TDI issues. I am also asking for your own suggestions on how these problems might be related and which component might be defective.

If someone is willing to join me on a VAGCom test drive for a reasonable payment and lives within 80 km of Wuppertal, I would be very happy .

Now, let's describe the problems:

- Intermittent and unusually strong starting weakness in the 900-1500 RPM range.
- Strong pulling power (as usual) up to 2700 RPM.
- Noticeable power drop between 2700 and 3000 RPM.
- Suddenly, at over 3000 RPM, the system returned to normal performance.
- The fuel consumption indicator usually doesn't climb as high as it used to when accelerating in 5th gear; it now only reaches 11.x liters per 100km, instead of up to 13.x liters per 100km. However, occasionally, when driving at full throttle, it still fluctuates between 13.x and 11.x liters per 100km.
- No error codes stored.
- The cruise control can no longer be set to higher speeds. On a straight road, the cruise control works up to about 160/170 km/h, less when going uphill, and more when going downhill. The accelerator pedal always adds about 30 km/h to the set speed.
- Top speed is normally reached.
- Climate out -> no difference.
- Disconnecting the vehicle from the battery for 30 minutes did not resolve the issue (did not reset the control unit).

Best regards, Pioneer.

Hello,

I experienced the exact same phenomenon with my AFN last year. The car had about 160,000 km at the time. A test drive with the dealer didn't reveal anything. The error memory was also empty.
In addition, the engine started losing coolant, and you should also check that. As the performance continued to decrease, I took it to my local car repair shop, had the compression checked, because I suspected a blown head gasket, and sure enough! It wasn't critical yet, but it's better to catch it early.
After the new cylinder head was installed, the engine ran better again, but not quite right. Eventually, replacing the mass airflow sensor (MAF sensor) restored the usual performance.
Here's the translation:

So much for the topic of 'there's nothing in the error memory, so everything is okay.' People who say that, in my opinion, really don't know what they're talking about.

Good luck with your troubleshooting.
Stefan.

Hello and thank you for the quick response.

Although I was almost certain it wasn't the cylinder head, I just checked it anyway. The coolant level hasn't changed even a millimeter in months, and the engine is perfectly clean and doesn't leak any oil. It also only has 78,000 km (approximately 48,000 miles) on it.

Is the LMM (mass airflow sensor) that plug-like component located in the intake hose, right next to the air filter housing?

Best regards, Pioneer.

Yes, that is the mass airflow sensor.

Disassemble it and spray the small wire inside with brake cleaner.
After that, reassemble everything and don't forget to plug the connector back in. Otherwise, you'll experience the performance of an SDI engine.

That might be the reason. I did the same thing on a friend's car yesterday, after it was the cause of the problem on my car last week. Now both cars are running well again.


Best regards,
Ralf

Hello,

Golfmann wrote:

Yes, that is the mass airflow sensor. Disassemble it and spray the small wire inside with brake cleaner.

Yes, in these cases, the values of the hot-film air mass sensor should definitely be checked.

You can find a table in the technical articles that lists the target values and measurement conditions for various TDI engines. You can then use a diagnostic system to check these values.
So, you can either use a laptop and build a diagnostic adapter (there's a specialized article on how to do that), or have a diagnostic test performed with a VAG tester.

If you have the possibility, it would be very helpful if you could temporarily install a mass airflow sensor from an identical, defect-free engine (engine code!) for testing purposes; this can be done in 5 minutes.

Here's another tip: all newer TDIs are equipped with what's called a hot-film mass airflow sensor, which doesn't use a hot wire to measure airflow, but instead uses a measuring surface.
However, whether cleaning will actually help when you're seeing fluctuating readings is questionable. In this case, I would suspect internal contact issues or problems within the cable harness.
But first, let's test whether the problem is actually caused by the hot-film air mass sensor (HFM).

Best regards, Rainer.

Pioneer1976 wrote:

- Sporadic, unusually strong starting weakness in the range of 900 - 1500 RPM. - Strong pulling power (as usual) up to 2700 RPM. - Noticeable power drop between 2700 and 3000 RPM. - Suddenly, at over 3000 RPM, the system returned to normal performance. - The fuel consumption indicator usually doesn't climb as high as it used to when accelerating in 5th gear; it no longer reaches 13.x liters per 100km, but only up to 11.x liters. However, occasionally, when accelerating at full throttle, it still fluctuates between 13.x and 11.x. - No error codes stored. - The cruise control can no longer be set to higher speeds. On a straight road, the cruise control works up to about 160/170 km/h, less when going uphill, and more when going downhill. The accelerator pedal always adds about 30 km/h to the set speed. - Top speed is normally reached. - Climate out -> no difference. - Disconnecting the vehicle from the battery for 30 minutes did not resolve the issue (ECU reset)

.
Hi.
To start with the last point: as far as we know, no TDI engine control unit has a permanent positive connection, so disconnecting the battery has the same (k)no effect as turning off the ignition .

The LMM (lambda measuring module) might be the culprit, but based on my own experiences, when I see these symptoms, I usually suspect the boost pressure control system.

"If VAG had equipped every TDI engine with a boost pressure gauge instead of, or in addition to, the at least 20 kilograms of sound insulation, hundreds or thousands of such cases could have been partially diagnosed with a single glance during the drive (boost pressure OK or not), without having to connect the diagnostic tool (OBD) and obtain the boost pressure curve through a complex process involving numerous electronic components."

But then, the workshops would have to fear a flood of "stupid" customer questions about the correct pressure build-up when accelerating - and customers who might "correctly" interpret the display when there are problems, possibly better than the workshops' own "experts" .
In addition, the workshops would be deprived of the opportunity for lengthy and profitable troubleshooting .

That should make it clear why no TDI comes with an LDA from the factory .

So, install an OBD scanner and observe it during the next issues your car has - it will probably be cheaper than the usual troubleshooting process by a regular VAG workshop.

Thank you in advance for all the answers .

Based on everything I've read so far, the cruise control still doesn't seem to fit the picture. Why can't the cruise control be set to higher speeds if the problem is related to the mass airflow sensor or the boost pressure control?

Apart from that, the low-pressure fuel pump (LMM) seems most likely to me, because if the boost pressure is too low, the full amount of diesel should still be injected, which would cause the car to produce soot and also show normal fuel consumption readings. Today, I asked a friend to follow me, and the car didn't visibly produce any soot.

This is, of course, my interpretation as a layperson, based on what I've read so far. Is this interpretation correct or incorrect?

And again: How does the cruise control fit into the picture?

'Since I don't trust workshops either, is there anyone in the Ruhr area, specifically Düsseldorf or Cologne, who is an experienced user with a VAG-Com and would be willing to help me troubleshoot issues for a reasonable fee? I don't want to buy all the equipment myself, and I'm not comfortable cleaning the mass airflow sensor or performing the engine diagnostics myself.'

Best regards, Pioneer.

I can imagine that the cruise control is operating under partial load, and that the values of the mass airflow sensor (MAF) are inaccurate in that specific range. If you now give it full throttle, more fuel is automatically injected, which bridges the power loss?

It's not really that difficult to disassemble the LMM (mass airflow sensor) and spray it with brake cleaner. I don't think you need to be an expert to do it.

However, as Rainer already mentioned, I would recommend doing a test drive and comparing the results with the target values listed on this page.

It might also be due to a stuck VTG (Variable Turbine Geometry) adjustment mechanism, which is only fully engaged at full load. If it's stuck in that position and not pulled tighter with vacuum, the cruise control will be affected again. At full throttle, the adjustment is engaged more aggressively, and this can overcome the stuck point.

What do you think about my ideas?


Best regards,
Ralf

Pioneer1976 wrote:

Apart from that, the LMM (Low-Pressure Fuel Management) seems most likely to me, because if the boost pressure is too low, the full amount of diesel should still be injected, which would cause the car to produce soot and also show normal fuel consumption values. Today, I asked a friend to drive behind me, and the car is not visibly producing soot.

Hi.

Your conclusion about the mass airflow sensor (MAF) is incorrect, because with too low boost pressure, less air is drawn in, which reduces the MAF signal.
And the LMM signal is one of the limiting criteria for the fuel injection quantity -> generally, more diesel should never be injected than can be combusted "soot-free."

If your car is still producing excessive smoke, other causes may be to blame.
The classics when it comes to performance loss and }soot are...
- an AGR valve that is not closing properly.
- Leaks between the charging port and the motor, which are usually noticeable by hissing sounds when the motor is supposed to engage.

With Holzhammer tuning, the engine may still produce soot, but it usually doesn't lose power at the same time.

I can see that nothing will happen without a test drive. Is anyone here with VAG-Com who would be willing to help me with that?

Hi,

Okay, silly question: how old is the diesel filter? It caused similar symptoms in my car before, but that doesn't explain the erratic behavior of the cruise control.

Best regards, Uli.

Hi, I forgot to mention this. That was also my first thought, and I've already had the fuel and air filters replaced.

Regards, Pioneer.

P.S.: Is there really no one who could help me out with a test drive using VAG-Com? I'm not asking for it for free...

Hello,

Here's a short report from the last few days. My G4 AHF automatic...
In the past few weeks, it hasn't been performing as well, especially when starting.
träge und wollte beim Kickdown nicht so richtig vom 3. in den 4.. When
Then, when I eased off the accelerator a bit, he shifted up and accelerated again.
beschleunigt - für mich eindeutig: kein Drehmoment. Smoked.
He didn't either. Because I've been quite busy lately, I just...
cleaned the LMM: without success. Last Sunday, I tried a little...
Time to connect VAGCOM and, among other things, perform a diagnostic test drive with logging.
Second gear, full throttle at 1500 rpm, with a marker set at 3000 rpm, and then...
Several times. Afterwards, I carefully analyzed the Excel file at the kitchen table.
and lo and behold: the mass flow rate did not exceed 710 - below the lower tolerance limit.
According to VW, it's part number 830! I'm ordering a new mass airflow sensor for my car tomorrow.
Long-time parts dealer - Picked up yesterday - Paid €190 - immediately.
built-in - runs like a dream!


Regards,

Jürgen.

Hi Jürgen,

I'm from Senden, near Münster. Hmm, Wuppertal, Düsseldorf. That's quite a distance. Maybe someone who lives closer can be found?


Regards,
arne

I assume you're talking about 'Jürgen'? Well, Münster isn't exactly around the corner, but it's reachable within an hour. I'd much rather drive there than waste hundreds of euros at one of those incompetent workshops.

I might be able to come to Senden next Friday through Sunday. Let's discuss this further via email: [email protected].

Best regards, Pioneer.

After weeks of delaying the repair, fearing high costs, I spontaneously drove to the Seat car dealership Stamm in Solingen yesterday and described my problem.

'LMM, please be understanding,' was the reply. I was told I could wait for 45 minutes, and then it would be taken care of immediately.

Now it's running again. After the gradual loss of performance, the 'upgrade' seems to have given the engine more power than ever before...

But I don't quite understand why the LMM could be responsible for all symptoms. Can someone explain how the following points fit into the picture?

Intermittent and unusually strong hesitation during acceleration in the 900 - 1500 RPM range - why intermittent? I always thought a faulty MAF sensor would provide gradually worsening values and not behave erratically.
- Strong pulling power (as usual) up to 2700 RPM - why?
- Between 2700 and 3000 RPM, there is a noticeable drop in performance - why is it so abrupt and not uniform?
- Suddenly, at over 3000 RPM, the system returned to normal performance. - why?
- The fuel consumption indicator usually doesn't climb as high as it used to when accelerating in 5th gear; it no longer reaches 13.x liters, but only 11.x liters. However, occasionally, when using full throttle, it jumps back and forth between 13.x and 11.x. - why is it fluctuating?
- The cruise control can no longer be set to high speeds. On a straight road, the cruise control works up to about 160/170 km/h, less uphill, and more downhill. Using the accelerator pedal always adds about 30 km/h. - This doesn't quite fit the picture, what does the cruise control system have to do with it?!
- Top speed is normally reached. okay, and now it's not happening anymore either.

Best regards, Pioneer.
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