Missing performance up to 2,500

Hello,

Sure, please provide the text you would like me to translate from German to English. I will only provide the translation without any explanations.

Volkswagen Golf 4, manufactured in 2000, with a PD AJM engine, 85 kW (116 hp), and 120,000 km mileage.

The car doesn't have enough power up to 2500 RPM.
The car is actually running perfectly fine; the sound, 'smoothness' of operation, etc., are all good. However, the turbo boost doesn't start to increase until around 1300 RPM, and it reaches its maximum value around 2000 RPM, but instead of increasing, everything remains constant, just at approximately 600 RPM higher.

'In other words, up to 2,000 RPM, the SDI is a nimble performer. Anything above 2,600 RPM and there are no complaints; it reaches its maximum power. However, if you hold it above 3,000 RPM, it becomes almost brutally powerful and delivers an abrupt surge of acceleration.'

After replacing the head gasket, the car started accelerating worse and worse after about 3,000 km. It also had cold start problems (which were resolved by replacing the temperature sensor).

No errors found in the fault memory. After a complete inspection (including Asle + 1551 - covering turbocharger pressure and control, EGR system and control, bypass valve, vacuum supply, etc.), the following work was also performed:
The intake path is completely clear and unobstructed, all hoses and pipes are sealed (tested from the turbocharger to the intake manifold, including the intercooler, with approximately 1 bar of pressure). The exhaust system is free of obstructions, and a catalytic converter and exhaust system that were removed from a functioning vehicle have been temporarily installed for testing.
After directly actuating the vacuum sensor on the turbocharger with a hand vacuum pump (i.e., bypassing all regulation), there was no change. The bypass valve was deactivated and 'fixed' in the open position.
Steuerzeiten überprüft, Pumpedüseelemente auf Ausrichtung und Grundeinstellung überprüft. KompExpression i.O.
Harness was measured multiple times (resistance and voltage drop were checked).
Fuel system completely drained and refilled (no dirt was present).

Meanwhile, the following ECUs (Engine Control Units) are new and have previously been replaced multiple times in functioning vehicles:

- Fuel filter (new)
- Temperature sensor (new)
- Charge pressure control valve (new)
- LMM (new)
- Turbocharger (new)
- Engine control unit (new)


My problem is that, apparently, the manufacturer doesn't provide test values for this load range (e.g., boost pressure, which is being measured at 3000 kPa - everything seems to be okay).

The car has never been fueled with rapeseed diesel.

Okay, I think I have everything together now.

I hope someone can help me.

Best regards, HHrasputin.

Hello HHRasputin!

Having already eliminated two primary suspects – the mass airflow meter and the turbocharger – I would now focus my attention on the charge air system, particularly the intercooler. You might have a leak somewhere that is preventing proper pressure buildup up to 2500 RPM.
Did you install a completely new turbocharger or a refurbished one? Was the variable geometry linkage really smooth? How about the adjustment of the control rod? Is it perhaps misaligned to the point that, when the turbocharger is at its maximum boost level (with the vacuum diaphragm fully engaged), the turbine vanes cannot be mechanically moved to their "aggressive" end position?Also, here's the translation:

"Check the exhaust manifold and the flange (if present) connecting to the turbo for cracks and leaks."

These are just some food for thought; maybe your mistake is among them!

Regards,
Alex.

Hello HHRasputin!

Having already eliminated two primary suspects – the mass airflow meter and the turbocharger – I would now focus my attention on the charge air system, particularly the intercooler. You might have a leak somewhere that is preventing proper pressure buildup up to 2500 RPM.
Did you install a completely new turbocharger or a refurbished one? Was the variable turbine geometry (VTG) linkage really smooth? How about the adjustment of the control rod? Is it perhaps misadjusted such that, when the turbocharger is at its maximum boost level (with the vacuum diaphragm fully activated), the guide vanes of the turbocharger cannot be mechanically moved to their 'aggressive' end position?Check the exhaust manifold and, if applicable, the flange connecting to the turbo for cracks and leaks.

These are just some food for thought; maybe your mistake is among them!

Regards,
Alex


Hi Alex,

All parts that are marked as 'new' are new and come from a reputable source.

Boost pressure side checked:
- for leak tightness (visual inspection and compressed air test).
- Checked for leaks (disconnected and sealed the hose from the turbocharger, disconnected and sealed the hose to the intake manifold - then pressurized with compressed air at 1 bar through a tire valve - pressure drop after 5 minutes was less than 0.1 bar).
- VTG vanes were also common in the old turbocharger (the new one has already been checked for proper operation).
- With the old turbocharger, I had the opportunity to test it on a dynamometer.
adjusting the setting on the VTG linkage yielded some improvement, but ultimately made no real difference - the new turbocharger remains unchanged!
- The exhaust manifold and turbocharger are a single component.
- The head gasket is new and tight.

Thank you.

Regards,

HHRasputin

Hi,

Have you already checked the hose to the vacuum sensor of the VTG control system?
If something is lodged inside, it prevents the pressure relief valve from functioning correctly, and therefore, insufficient vacuum pressure reaches the charging cylinder, preventing it from being pulled into the "maximum charging pressure" position.
The solenoid valve in the aforementioned vacuum line is also a potential candidate (crack at the connection nipple).

Greetings, Raine.

Hi,

Have you already checked the hose to the vacuum sensor of the VTG control system?
If something is lodged inside, it prevents the pressure relief valve from functioning correctly, and the charging system cannot reach its maximum charging pressure.
The solenoid valve in the aforementioned vacuum line is also a potential candidate (crack at the connection nipple).

Greetings, Raine.

Hi Rainer,

All hoses related to the turbocharger pressure regulation, EGR valve control, and bypass valve were first inspected, and even though they were found to be in good condition, they were also replaced.
The turbocharger wastegate valve was checked and found to be in good working order, but it was replaced anyway.
To ensure everything is excluded according to the regulation, the bypass valve of the VTG linkage was directly connected to a hand-operated vacuum pump with a pressure of 600 mbar vacuum (also tested up to a maximum of 900 mbar). The vacuum pressure should be at least 600 mbar – mine is around 750 mbar vacuum.
All pressures, whether vacuum or boost pressure, have been checked using a pressure gauge and compared with measurement blocks 10 and 11. 100% OK.

I also checked the tandem pump for fuel and vacuum, and everything was fine – but I replaced it anyway. Still experiencing the same problem.

My next steps will be:

Replace the sealing rings of the injector elements.
Replace the injector nozzles.
3. Replace the dual-mass flywheel (I've heard there can be problems with it - this was on a Sharan PD, which experienced misfires in one cylinder and loss of power - the misfires would shift between cylinders, meaning that at idle, one or two common rail injectors were always operating in the negative range). // In addition to replacing the dual-mass flywheel, the entire engine was also replaced under warranty because the dual-mass flywheel was defective - ???

What do you think about what I'm planning to do?

I would be really interested to hear your opinions on this.

I haven't given up on any problem yet and I've solved them all so far, but this [censored] is driving me to the brink of madness – maybe I'll be a little closer to solving it tomorrow – haha – at that point, I won't care anymore because I'll be completely crazy.

Greetings, HHrasputin.

Have you also checked the hoses for cracks, specifically the charge air cooler hoses and the charge air cooler itself?
Unusual noises?
Does the car emit black smoke when accelerating to full throttle within the RPM range where there is no power output, or does it not do that?

Best regards, Rainer.

Have you also checked for cracks in the turbocharger hoses and inside the intercooler?
Unusual noises?
Does the car emit black smoke when accelerating to full throttle within the RPM range where there is no power output, or does it not do that?

Greetings, Rainer.

Hello Rainer,

Schläuche sind wie neu und eben wie beschrieben mit 1 bar abgedrückt. (incl. L(LK)

The noises are completely normal (it's a bit louder when cold, but I experience that with other vehicles too).

It doesn't produce any smoke or similar emissions, regardless of the engine speed or load.

Greetings, HHRasputin.

Hello everyone,

habe noch die Dichtringe der Pumpedüseelemente ersetzt. No improvement.

The car was sold with the defect.

From what I understand, he exports directly.

Well, you can't solve every problem; after all, a car is just like a person.

Thank you for the tips.

Greetings, HHrasputin.