ALH Engine: Power Boost Above 2500 RPM - VW OK

'For quite some time, I've been dealing with a sluggish Golf 4 ALH (165,000 km). I've already searched the forums, but haven't found anything relevant.'
The Syntome:

-Increased consumption , 0-1.5 L
- Up to 2500 RPM, only moderate power delivery (previously, there was a significant power boost starting at 2000 RPM).
- However, from 2500 RPM onwards, there is a significant increase in performance, reaching approximately 2800 RPM.
-requires only a small amount of power.
- Top speed: 160 km/h
-The increase in performance is more stepped, and far from being as smooth as it used to be.


Connected to the VAG diagnostic system -> everything OK, the mass airflow sensor (MAF) was slightly faulty -> replaced -> symptoms are now less noticeable.

When asked about the boost pressure, the mechanic explained: 'There are only small fluctuations, a maximum of 200 millibars. (I find that quite significant, considering the maximum boost pressure is 0.9 bar).'
VTG is working smoothly, pneumatic system is okay, diesel filter is new, fuel flows bubble-free.

The AGR (Abgasrückführung valve) is also fine; it seals properly.

The pump setting can be adjusted from 57 (???) to 68 (I have no idea what this means), but it likely indicates a relatively late adjustment.

I'm completely out of ideas about where the problem might be.
My suspicion now falls on the pump setting, the flow control valve, or the injection timing adjuster.

The high fuel consumption is really stressing me out, especially with these gas prices.
I really need a solution right now.

Try typing "wavy" into the search bar; maybe you'll find something that can help.

I've already checked it. There are no issues detectable with the pneumatic control, the loading hopper, the VTG linkage, etc. The mass flow meter has been replaced.

I recently swapped the pneumatic valves from AGR and the turbocharger.

The difference was so significant that after restoring it to its original state, I initially thought I had mixed something up.

When the AGR control valve functions as a boost pressure regulator, the engine's responsiveness is noticeably improved. However, the stepped acceleration behavior is still present.

Hello flightmaster!

You probably have too little boost pressure at low RPMs! Here's how you can test it.
/viewtopic.php?t=10428&highlight=1400
At 1400 RPM, a pressure of 100-200 mbar should be present.

It would be great to use VCDS to record the boost pressure.

Unfortunately, I don't have a VAG-COM. However, that's mainly because I don't have a laptop.

Das mit dem Ladedruck war meine erste Idee und bin damit zu VW. But those are mine.
That would be great, everything is fine.

The sudden jump in performance of 2500 RPM is driving me crazy.

I just observed the VTG (Variable Turbine Geometry) vanes with my girlfriend. They open and close smoothly and evenly when the engine is idling and the throttle is slowly increased.

I'm pretty much at the end of my rope.

P.S. The replacement mass airflow sensor now has a different part number.

Old LMM part number: 06A 906 461.
New LMM: 038 906 461 C.

I specifically contacted VW again to confirm if that was correct.
I have it in writing that the mass airflow sensor (MAF) will be replaced with a new one.
The new one has a small insert in the grid that looks like an air deflector, designed to better direct airflow to the sensor.
If you're interested, I'll take a picture.

Can a pump that is started later also produce such performance fluctuations?
Or perhaps advanced engine wear? If too much air is forced into the intake manifold through the crankcase ventilation system, the turbocharger would simply circulate the air and exhaust gases continuously.

P.S.S. It doesn't produce any smoke at all!

flightmaster wrote:

Unfortunately, I don't have a VAG-COM.

This is mainly because I don't have a laptop.
Hi,

Your case is once again typical of the question "spending money for..."
a) Frenzied exchanges among the Friendly and the Unsuspecting, or...
b) a VAGCOM diagnostic tool.

The chance to quickly fix the error is higher with option b) and with our help .

Quote:

I have it in black and white that the mass airflow sensor (MAF) will be replaced with the old one. The new one has a small insert in the grid that looks like an air guide to better ensure the airflow to the sensor.

The new version is the "Longlife" version, which offers better protection against water and particle ingress for the sensitive measuring membrane.

Quote:

Can a pump that is started later also produce such performance fluctuations?

Less likely, but a hanging injector nozzle adjuster is more probable -> a check is easily possible with VAGCOM.

Hello,
Is the AGR and its vacuum lines really okay? The behavior reminds me of my AGR test series, where I only had a small piece of plastic film attached to its vacuum connection - a hose was placed on it, and then I started the engine - until after about 100 km, this behavior with a sudden power increase started. The plastic film had given way a little, and the vacuum control was acting very slowly (especially the closing process, which was also very delayed). After stopping the engine, everything was fine for a moment.
Best regards,
Andreas

Do you mean that indirectly: Should we first deactivate the AGR (Abgasrückführung system)?

I once sucked on the vacuum hose of the pressure sensor while the pressure hose was disconnected. The valve seems to open very sensitively, as far as one can tell visually.

Okay, I'm going to install this old metal piece into the EGR connection on the exhaust side. Let's see how it holds up.

I had it installed before, but I removed it again because of the noticeable noise after the engine was turned off and the even longer warm-up time.
The car still has a while to last.

I've apparently found the cause of the low torque.

I temporarily removed the front part of the air intake duct to clean the filter. There wasn't much in it.
Then I thought, why don't you try driving around without the filter?

And now, here it comes...

Even with the first press of the accelerator, the turbocharger spooled up much earlier, and the power delivery was significantly improved.
As a test, I reinstalled the part -> the engine felt noticeably weaker.

I then decided to test driving without the air filter for 4 weeks. This resulted in noticeably better acceleration, a significant increase in torque from 1800 RPM, improved engine responsiveness, and a reduction in fuel consumption of approximately 0.2 liters.

Today, I found an article using the search function that states VW recommends removing this filter because it has been incorrectly installed in vehicles that were actually supposed to be delivered to Northern Europe.

In my case, it seems that this is actually the solution to the problem.
Simply cleaning the filter won't achieve anything.

MFG