Audi 2.5 TDI: No Power in 1st & 2nd Gear

Hello

My name is Manuel, and I've had my Audi A4 Avant Quattro with a 2.5-liter TDI engine for about six months. The car had been owned by four different companies before it came to me. So far, everything is great, except for this small issue:

When accelerating in first gear, it feels like the engine isn't being turbocharged – it slowly builds up the RPM, and it almost feels like you're falling asleep.
In second gear, it's already better; you can tell that the engine actually has much more power than it lets out in first gear.
It runs perfectly in 3rd gear and accelerates smoothly.
I initially thought it was a leak in the vacuum system – I even found a hose with two small cracks and immediately replaced it. Unfortunately, that didn't improve the situation.

'I've now purchased an OBD connector, read the error codes, and after many attempts, finally recorded the boost pressure during acceleration. VAG COM shows a value of approximately 2100 mbar in 1st gear at just below 4000 RPM – the same amount as in 3rd gear. So, it probably isn't related to the boost pressure.'


Either the mass airflow sensor or the fuel injection pump is sending incorrect signals, or I don't know what else - I'm at a loss. So far, no one in any forum has been able to offer any information about this problem. I hope you can help me - Where should I look for the problem next? - And question number 2: To what extent can the engine control unit or the engine maps of the control unit be modified (e.g., controlling the turbocharger based on engine speed)?

Another problem:
I can't access certain control units, such as the engine control unit, using VAG COM. The tool displays this warning: 'Incorrect login because the connection was interrupted' - followed by an error message stating that there are too many errors in the data transmission to proceed. I only regain access to the car when I turn the control unit off and on again. The login was 12233, and the Audi is a B5 model from 1998.

Best, Manu.

F41TH wrote:

When accelerating in 1st gear, it feels like the engine isn't being turbocharged - it pulls the RPMs up relatively slowly, and you almost fall asleep while doing it. In second gear, it's already better; you can tell that the engine actually has much more power than it lets out in first gear. In 3rd gear, it works perfectly and accelerates smoothly.

Have you read this already?
/viewtopic.php?t=21874&start=0&postdays=0&postorder=asc&highlight=

What interface hardware are you using, and which version of VAG-Com?

The login is incorrect. 26262 might work. However, is it even worth trying to log in if the communication might be disrupted?

When accelerating in the first gear, it feels like the engine isn't being turbocharged - it pulls the RPMs up relatively slowly, and you almost fall asleep while doing it.
In second gear, it's already better; you can tell that the engine actually has much more power than it lets out in first gear.
In 3rd gear, it works perfectly and accelerates smoothly.

Have you read this already?
/viewtopic.php?t=21874&start=0&postdays=0&postorder=asc&highlight=

What interface hardware and which version of VAG-Com are you using?

I've read it, but it's not helping me.
'I checked the camshafts when I bought the car - everything was fine then. The engine is supposed to have only about 10,000 km on it, and that seems to match the condition of the camshafts. You can tell they've been used, but there's no sign of wear. I haven't checked the lifters.'

What surprises me is that I can do almost everything with VAG COM that the unregistered version allows. It's only when I try to access the engine control unit or briefly turn off the ignition that the program reports errors.

'So far, I've recorded data on boost pressure and torque regulation, and the boost pressure is constant across all gears at roughly the same engine speed (around 4000 RPM at 2100 mbar). All other values seem to be more dependent on engine speed than on, for example, different gears or the varying force required to move the vehicle forward. However, this doesn't feel quite right when accelerating in the first two gears.'
'I mean, the Audi is drivable as it is, but in the long run, it's extremely annoying because in the first two gears, you're left standing by every car with even 30-40 horsepower.'

The repair manual mentions a fuel injection quantity limitation for/due to:
• Torque limitation via speed.
• Air intake mass (to prevent smoke).
• Wheel slip
• Motor drag torque


Ich werde jetzt mal die Anzeigegruppe Nr. 11 loggen, also Motordrehzhal, Ladedruck soll, Ladedruck ist und Ansteuerung der Ladedruckbegrenzung. Mal sehen was dabei raus kommt. I will report.


What does that mean? Theoretically, one could...

Okay, I'm back from about 5 hours of experimenting.

I've discovered that the boost pressure is significantly lower than it should be in the first two gears. However, at full load in higher gears, the boost pressure is almost identical to the target values.
The LMM (lambda sensor) was replaced today with a genuine Bosch part.
I found another brittle hose in the undercarriage system - I replaced it, but there was no change.
Disconnecting the EGR valve provided a temporary fix (during the first acceleration in 1st or 2nd gear) – the engine ran great, the RPMs immediately reached near the redline, but then the power suddenly dropped again.
When I connect the turbo to the vacuum system, the linkage of the variable turbine geometry (VTG) moves upwards, but not all the way to its upper limit. If I apply the vacuum directly to the diaphragm or blow into the hose, it moves to the upper limit within a few seconds.
All the connections are made as described in the repair manual. Disconnecting the EGR valve doesn't make a noticeable difference. Something about this all seems very strange to me. I'm going to read the error codes again, disconnect the EGR valve and this strange valve in front of the intake manifold, and then test drive it again.

F41TH wrote:

Okay, I'm back from about 5 hours of experimenting. I've found out that the boost pressure is significantly below the target value in the first two gears. However, at full load in higher gears, the boost pressure is almost identical to the target values.

Forget about the values in the lower gears. The acceleration is too fast in those gears for the few values provided per second to establish a stable settling behavior. That's why expert articles always emphasize logging data in the highest possible gear! A sudden full throttle from 1,400 RPM in 3rd or 4th gear to 4,000 RPM should be sufficient.

If the pressure was correct, the next step is to check the difference between the desired and actual air mass. This makes me think about what the EGR system is doing.

Quote:

Disconnecting the EGR valve temporarily (during the first acceleration in 1st and 2nd gear) seemed to help - the car felt great, the RPMs immediately reached near the redline, but then the power suddenly dropped again.

When it comes to the mass airflow sensor (MAF), I would only use the original part. As far as I know, Bosch MAF sensors provide different readings. To rule out the MAF as the cause, you can also simulate it with a diode. However, when doing this, the EGR (Exhaust Gas Recirculation) system must be disabled!

Insufficient air mass can also be caused by the camshaft. Insufficient lift results in insufficient mass.

I suspect the problem lies with the vacuum control system, possibly the control valve. The VTG (Variable Turbine Geometry) *must* be at its upper limit in idle; otherwise, the behavior you're describing is perfectly normal. Try swapping the control valve from the EGR (Exhaust Gas Recirculation) system with the one for the VTG. This will help you determine if the problem is related to the valve itself. Just make sure you connect the hoses in the correct orientation.

Thank you all for your help, the problem is solved .

I followed the suggestion from mserge and checked the vacuum system.
I replaced all the vacuum hoses because some of them were already starting to become hard.
In this case, the performance values have deteriorated further.
I did some more research on the topic and found out that the VTG (Variable Turbine Geometry) should be at 100% when the engine is idling, but that wasn't the case with mine.
After that, I found the problem: the N75 valve was stuck, allowing a constant amount of fresh air into the vacuum system while not fully opening the vacuum 'supply' to the turbo's control port.
I removed the valve, inspected it, and after applying some penetrating oil, it opened and closed completely and sealed properly.
After the installation, I barely recognized my Audi. It has full power and a relatively responsive power delivery, plus increased power in the lower gears - it couldn't have been better.
If I have time today, I'll do another log run to see if everything is within the normal range, but even now, it's performing very well.

Hello everyone, I'm new here and I'm also experiencing performance issues with my A6.
The car has only about half the power, and it has no acceleration, as if it had a 60 hp diesel engine. The turbo is okay, and I even swapped the mass airflow sensor (MAF) with one from a friend... okay, he has the same engine but as an automatic, but I think it's the same MAF, right? Does anyone have any idea? Could it also be the fuel filter? Because when I open the oil filler cap, the camshaft actually looks good. I would really appreciate any help.

You can only see one of the 24 camshaft lobes through the opening.

Otherwise, you should consider taking a logging trip.