Power loss in TDI engine despite maximum speed

Hello,

My brother drives a Volkswagen Golf IV TDI, manufactured in 1998, with an engine power of 66 kW and approximately 215,000 kilometers on the odometer.

When accelerating quickly, you'll notice starting from the 4th gear that power drops off around 2500 RPM, as if you were slightly lifting off the accelerator. However, the vehicle continues to accelerate (just not as rapidly). The same thing happens in 5th gear. The top speed is still reached.

The performance is not dependent on the engine speed. If you press the accelerator again after the power decreases, you'll get a boost for a few seconds before it diminishes again. This can be repeated multiple times, even at higher speeds.

I couldn't find any relevant entries in this forum. With the other issues, you always had to restart the engine immediately. That's not the case here.

The engine had never had any problems before, but suddenly the turbocharger failed. We were driving at 220 km/h (approximately 137 mph) through the Kassel hills when it happened. After a restart, it worked again. It must have been the emergency program kicking in.

Does anyone have any ideas?

Regards,
Sausage blinkers.

Hi,
It sounds like the fuel injection amount is being reduced because there isn't enough air available.
or rather, seems to be.
- Air mass sensor.
- faulty exhaust gas recirculation system.
- installed air filter
- obstructed airways

Check the screws as needed and repair them if necessary.
Otherwise, it's best to use a VAG-COM device to read the error memory (to see if there are any stored errors).
and compare the actual performance of relevant ad groups against their planned targets.

Best regards, Rudi.

Wurstblinker wrote:

Ich habe hier im Forum keine passenden Einträge gefunden . . .

Hi.

If Rudi's tips don't lead to success, there are, of course (unfortunately), other options available.
-> Technical article on troubleshooting with VAGCOM.

By the way, I think the power loss can also be present in the lower gears, but you don't notice it as much there because almost no air resistance is slowing you down.

Hi there,

Mine exhibits exactly the same behavior, except for the emergency mode.
Since I also have a dashcam in the car, it's very clear what happened at that moment.
You press the accelerator, and the boost pressure increases rapidly depending on the engine speed and gear. In my case, it reaches values of around 1.4 bar. This lasts for about 3 seconds. Then, it suddenly drops to approximately 0.5 bar of boost pressure and slowly rises again to 0.9 bar as the engine speed increases. At the moment when the boost pressure drops, I also notice a sudden loss of power. This is particularly noticeable during overtaking maneuvers on country roads or in the acceleration lane of a highway entrance ramp.
I suspect the cause is a stiff VTG (Variable Turbine Geometry) mechanism. It has been checked by the workshop before, but they didn't find anything wrong.

I achieve maximum acceleration by not immediately applying full throttle, but rather using about half throttle until the first 'reduction in boost pressure' occurs. Then I apply full throttle, and the boost pressure quickly builds up to 0.9-1 bar. Because the overshoot is not so large at that point, the engine control unit doesn't have to reduce the boost as much, and the boost pressure only drops briefly below 0.9 bar.

'It's kind of bad, but what can you do?' - According to the test results, the boost pressure is 0.9 bar at 3000 RPM, and that's apparently acceptable. - Statement from the workshop.

Since my car is also a company vehicle, I can't fix it myself and I guess I'll just have to live with it.

Regarding your problem: It seems like the system is malfunctioning even worse for you than it does for me. Therefore, it eventually triggers the limp-home mode due to the excessively high boost pressure that lasts for too long.
You can probably best understand this by using a boost gauge. You can find those on eBay. You can simply connect it to the rubber hose in front of the intake manifold of your ALH engine with a tube and a syringe needle (just insert it into the inside of the curve so that less oil leaks out).
That's exactly how I did it, and it's been running in the system for over a year now.

Regards,

Eike.

Hi everyone.

I'm familiar with that problem too. I've posted about it before.
'On my AFN engine in a VW Golf 3, the boost pressure would also rise to 1.4 bar, then drop to 0.6 bar, and increase again to 1 bar with increasing RPM. Also, the behavior of initially having half-throttle and then full throttle resulting in full boost pressure is something I experience as well.'

I've fixed the problem now. It seems like it was caused by the mass airflow sensor in my case. I cleaned it, and now it runs like new again.
It wasn't the charger that was the problem for me, because it was brand new.



Best regards,
Ralf

PS: Could you please let us know if it was related to the same issue for you?

Hi,

Have you all ruled out the magnetic valve for limiting boost pressure as the cause?
That is often the reason for the symptoms described.
It doesn't cost much (10-15 euros) and it's worth trying to swap them out just to see if it makes a difference.

Hello Ralf and Wurstblinker,

Golfmann wrote:

Hi everyone. I'm familiar with that problem too. I've posted about it before. "With my AFN engine in my Golf 3, the boost pressure would also rise to 1.4 bar, then drop to 0.6 bar, and then increase again to 1 bar as the RPM increased. Also, the behavior of initially having half-throttle and then full throttle with full boost applies to me as well." I've fixed the problem now. It seems like it was caused by the mass airflow sensor in my case. I cleaned it, and now it runs like new again. It wasn't the charger that was the problem for me, because it was brand new. Best regards, Ralf PS: Könnt ihr mal posten wenn´s bei euch auch daran lag!

If it was the mass airflow sensor causing your problem, I'll eat my broom.
It's purely coincidental that it no longer occurs after the cleaning.

In my opinion, the following causes may be responsible for problems with charge pressure regulation:
- VTG is mechanically jammed.
- Vacuum sensor defective.
- Vacuum hose damaged/leaking/kinked.
- Faulty boost pressure sensor/wiring.
- Faulty magnetic valve for turbocharger pressure regulation.

The problem known as "Wurstblinker" sounds like a clogged diesel filter or a faulty fuel tank vent.
"@Wurstblinker, what does the error memory directly indicate after the error occurs?"

Best regards, Rainer.

Hello Markus.

So, the solenoid valve is also brand new for me. It can't be the problem there.
As far as I know, all the engines are equipped with VTG turbochargers. Therefore, the valve doesn't cost 10-15 euros, but I believe it costs around 68 euros.
It's definitely very expensive.

Best regards,
Ralf

Hello,

Okay, I'll write this myself. So, thank you for the answers. In the meantime, I've tried a few things:

1. Air filter and mass airflow sensor cleaned - no improvement.
2. The hose connected to the exhaust gas recirculation valve was disconnected - but it makes no difference.
Replaced the fuel filter and cleaned the hose before the air filter housing (some models have a small screen there, which accumulates dirt over time) - no improvement.

I also had the error memory read out. It doesn't show any errors.
The nice man from VW mentioned that an error message should appear if the VGT linkage is stuck. So, I can probably rule that out as a potential cause, right?

What is the cost of the mass airflow sensor (MAF)? The Volkswagen technician also mentioned that it's often a source of problems.

Best regards,
Malte

Hi,

Wurstblinker wrote:

... I also had the error memory read out. It doesn't show any errors. The nice man from VW mentioned that an error should be displayed if the linkage of the VGT is stuck. Then I can probably rule it out as a source of the problem, right?

No, that man told you nonsense. Read and understand the technical article about VTG.

Wurstblinker wrote:

What is the actual cost of the mass airflow sensor (MAF)?

The Volkswagen technician also mentioned that this is often a source of errors. }
Expensive.

Best regards, Rainer.

Hi,

Wurstblinker wrote:

Was kostet eigentlich der LMM?

It's somewhere between €270 and €290. At a large online auction house , you can already find new Lambda sensors for €150, and slightly used ones for €70. Another option is the DC Lambda sensor (already discussed in this forum), but it seems to have poorer performance at lower RPMs.

And that's why -> you absolutely must do a dyno run, paying attention to boost pressure and air mass readings.

Don't forget to adhere to the operating conditions; please refer to the technical article for the target values of the various engines.

Also, take a look at how the system settles in by giving it full throttle at 3000min ^-1 and observing the turbocharger pressure regulation process.

Best regards, Rainer.

Hello.

It sounds similar to what I'm experiencing (G IV '98, ALH engine, 98,000 km).
There's a noticeable drop in power between approximately 2500 and 3000 RPM, where the engine pull-off decreases significantly. Above that speed, the power increases sharply again, which allows the maximum speed to be reached.
It's noticeable that this only happens in the 4th and 5th gears when I fully accelerate from a low speed, especially under heavy load (with many passengers, luggage, or going uphill).

For me, the most likely cause is the turbocharger boost pressure. I wouldn't rule out the EGR valve either, as it should be active in that RPM range (I cleaned mine about 20,000 km ago - who knows, maybe it's already clogged again). Otherwise, the VTG adjustment seems plausible; it might not be adjusting properly because it's stuck.

The VTG valve previously showed a sporadic short circuit to ground as an error entry some time ago, so it remains a potential candidate for the problem.

Unfortunately, I still don't have a way to get a diagnosis: (.

By the way: Can you actually log data with the trial version of VAG-Com, or do you need a different version for that?

The trial version of VAG-COM is sufficient for data logging. However, a graphical analysis is, in my opinion, only possible with the full version of VAG-COM. But anyone who can create charts using Excel only needs the demo version.

Hi,

I experienced the exact same effect with my AFN.
(and I still have it - I've been searching for it until 1:00 AM yesterday and have gathered data).

It initially accelerates well, but then it feels like I'm losing power.

Vag-Com: (The demo version is sufficient) The ESP control is at its maximum limit (96%). The injection timing advance initially increases along with the target value, but then drops rapidly to several degrees before top dead center (TDC), while the target remains at around 15. This drop in 'advance' is noticeable as a loss of power. Maximum fuel injection amounts, mass airflow sensor readings, etc., have all been checked and are okay.

Also, sometimes the car wouldn't start right away if it had been sitting for a while.

The solution to the riddle: 2 errors.

Here's the translation:

1. The ESP is initially set too late, as indicated by the timing check (unlocked with VAG-Com). This means the injection timing is already at its maximum limit. However, a value of approximately 13 degrees can still be achieved with the injection timing adjustment if everything else is correct, so this doesn't explain why the 'advance' setting is decreasing.
2. Fuel line leak / High intake resistance / Fuel line connection.
The ESP (Electronic Stability Program) is drawing more and more air the more it's connected to the fuel line. When idling, it's fine; the pump is full, and there's no air in the line.
Acceleration:
The engine revs up, pressure builds in the pump that powers the fuel injection system, and the car accelerates normally.
Due to the significantly lower pressure in the line, it suddenly sucks in air. This air entering the EGR valve causes a dramatic drop in internal pressure, and the injection timing shifts almost to 0 degrees, which feels like the engine is losing power.

How can you determine if the same applies to you?
Simply observe the actual fuel injection start compared to the desired behavior, and check if the fuel injection adjustment still has a range of operation at full throttle/high RPM, or if it's already hitting its limit (more than 90%).

As mentioned above, I'm still experiencing the issue partially because I unfortunately couldn't get either a fuel hose or clamps last night.

How else can we test this?
Fill the diesel into the canister, connect the fuel line, test drive it and log the data to see if anything improves.

Question to everyone:

Is it normal for the basic settings of the ESP to shift over time, or is this something I should blame on the workshop that last changed the timing belt?

Is there anything in or around the tank that could cause a blockage?

garth.brooks wrote:

2. Leaky fuel line / High intake resistance / Fuel line to. The ESP (Electronic Stability Program) is drawing more and more air the more it's connected to the fuel line. When idling, it's fine; the pump is full, and there's no air in the line. Acceleration: The engine revs up, pressure builds in the pump that powers the fuel injection system, and the car accelerates normally. Durch den viel höheren Unterdruck auf der Leitung saugt er auf einmal Luft an, durch die Luft in der ESP bricht der Innendruck förmlich zusammen, Die Spritzverstellung fällt fast auf 0 Grad, das fühlt sich dann an wie Gas weg.

Hi.

This basically reads like a confirmation of my theory regarding...
I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.

Do you see it the same way?