Power loss at low RPM, Bora ASZ

Hello everyone!

I sold my Golf 4 TDI, with engine code AHF and 270,000 km, about a month ago, but I've decided to remain loyal to the brand.
The car is a 2003 Bora Variant with an ASZ engine and ERF transmission, with 50,000 km on the odometer.

I've read in several articles that the PD, with its 96 kW, supposedly has a 'slight hesitation' when starting. According to the torque curve, it should perform better than the AHF! That doesn't mean that the soot limit kicks in as a lower limit for the rev range, around 5 seconds, as soon as you accelerate out of the low RPM range, does it?
My AHF (Academic Honor Fellowship) was significantly better , but I also knew that some expensive repairs would have been my responsibility.

I have already discovered one error: two hairline cracks in the connecting hose of the vacuum pump to the power brake booster , and that after 2 years . Of course, the friendly salesperson did that for free, since I had pointed out the loss of power when I bought it!
I initially thought this might be the problem, that there wasn't enough vacuum pressure at the VTG in the lower RPM range.

I created various logs using Vagcom, specifically focusing on the 3rd gear performance starting at 1400 RPM, while driving slightly uphill, and of course, under full throttle.
I have the feeling that until 1700 RPM, the car acts like a naturally aspirated diesel engine. However, at 1800-2000 RPM, it vibrates so much that it hurts my back. It's not really beautiful.

I have already tested the VTG (Variable Turbine Geometry) using a vacuum pump. The adjustment lever moves, indicating a vacuum of -0.1 bar, and it continuously adjusts until it reaches its limit at approximately 600-700 mbar. I still went through the series of injections, but it didn't improve anything!

I need something concrete for the friendly mechanic, but before I mentioned anything about a diagnostic tool, the master mechanic there was already trying to dismiss me: 'That's within the normal variation, it's working fine, the mass airflow sensor (MAF) values are at the maximum !

It would be great if someone could take a look at the logs and provide some feedback.
I suspect the adjustment bolt for the VTG (Variable Turbine Geometry) system. What do you think about that?

Best regards, Ferdi, and have a pleasant weekend!

P.S: Sorry about the messy diagram in Measurement 1 , hopefully the diagrams in Measurement 2 are more informative .

Ferdi wrote:

I created various logs using Vagcom, specifically focusing on the 3rd gear performance starting at 1400 RPM, while driving slightly uphill, and of course, under full throttle. I have the feeling that until 1700 RPM, the car acts like a naturally aspirated diesel engine. However, at 1800-2000 RPM, it vibrates so much that it hurts my back. It's not really beautiful. I have already tested the VTG (Variable Turbine Geometry) using a vacuum pump. The adjustment lever moves, indicating a vacuum of -0.1 bar, and it continuously adjusts until it reaches its limit at approximately 600-700 mbar. I still went through the series of injections, but it didn't improve anything! I need something concrete for the friendly mechanic, but before I mentioned anything about a diagnostic tool, the master mechanic there was already trying to dismiss me: "That's within the normal variation, it's working fine, the mass airflow sensor (MAF) values are at the maximum !

"
Hi Ferdi,

First of all, I want to compliment you on your logs; your "problem" is well-documented within them.

However, after quickly reviewing it, I can't identify any major errors – the 96kW engine simply "sounds a bit unharmonious" when coming out of its low RPM range.
Log on to the same route, but in the 4th or, even better, 5th position. Engine speed from 1300 rpm to approximately 2000 rpm, full throttle, only using cylinders 8 and 11.
"This will provide more samples, the LD build can better keep up with the rpm updates, and I can compare it with my own logs."

Hi Ulf,

I've already done the acceleration tests, but I'll check the logs later today.

What also occurs to me is that I can rev the engine up from low RPMs more quickly by gradually increasing the throttle, compared to immediately flooring the accelerator. This is particularly noticeable in the 5th or 6th gear.

Sniff, I want my AHF back .
Okay, that one wasn't easy either. It had 216 injectors, plus a switchable control unit! I'm glad the control unit was switchable, because the clutch was completely worn out by the end. It could only be driven with the engine switched off.

Well, the Bora isn't bad overall, and if it comes to that, there's still Rainer , and I'll definitely do something about that. In terms of performance, the Golf with the larger nozzles was comparable to the Bora. But the 6th... The walk is really beautiful!

Okay, just a quick question: Is the top speed reached in 6th gear?
It just takes forever for him to reach 200!
I guess I'll have to try out your technical article on how to adjust the valve timing!
I noticed in MWB 4 that the ignition timing is set to 1.5 degrees before top dead center (BTDC) at idle!
Does this suggest that your 3-degree advance adjustment, moving towards a more 'early' timing, improves rotational smoothness in the higher RPM range?

Let's go log rolling!

Best regards, Ferdi.

Ferdi wrote:

I guess I'll have to try your technical article on adjusting the valve timing! I noticed in MWB 4 that the ignition timing is set to 1.5 degrees before top dead center (BTDC) at idle! Does this suggest that your 3-degree adjustment towards advance leads to better responsiveness at higher RPMs?

No! MWB 4, among other things, displays the "electrical boost start," which is generally not related to the NW setting.

Hello Ulf,

As promised, here are the acceleration logs for uphill driving in 4th and 5th gear, as well as in 2nd gear. I initially thought he wouldn't make it through the fifth grade, but it just took him some time.

I did another log hauling trip in the third gear on a flat road. But, as I said, this is only valid up to +/- 2000 RPM.

Luckily, I have a vacuum gauge and a vacuum pump available from work. I connected a T-piece and a hose to the VTG (Variable Turbine Geometry) sensor and tapped into the interior during driving. I noticed the following: At idle, according to the Vagcom diagnostic tool, the maximum boost pressure is being controlled at approximately 24% duty cycle and -0.6 bar according to the vacuum gauge. As soon as I start driving, the vacuum decreases to -0.55 bar at approximately 1100 RPM, and continues to decrease as it should. If the vacuum pump doesn't generate enough vacuum, wouldn't the LD (laser diode) setup shift to higher rotational speeds? Or am I mistaken?
Okay, the maximum vacuum pressure measured from the vacuum pump is -0.8 bar, which should be acceptable!
Hmm, I need to think about that carefully. I'm open to suggestions!

Now I've connected the manual vacuum pump directly to the VTG sensor and, using the pressure gauge, I've determined that the VTG adjustment lever is at its limit at -0.65 bar! Then there's a fundamental difference of 50 millibars, could that be so crucial?
Now I'm wondering, if even at 1100 RPM, only -0.55 bar of boost pressure is available from the wastegate solenoid, could this be the solution to my problem!

What amount of vacuum pressure is actually required at the maximum VTG (Variable Torque Gear) engagement point?

Okay, maybe there's something else we can see in the logs. In my opinion, the actual boost pressure is building up too slowly, which makes sense if the electrical power is limited, right?

Best regards, Ferdi.

Ferdi wrote:

As promised, here are the logs of the acceleration in 4th and 5th gear going uphill, as well as in 2nd gear. I initially thought he wouldn't make it through the fifth

, but it just took him some time.
Hi Ferdi,

Compare your logs with mine.
/viewtopic.php?t=10857&start=16

Although I have the "slightly smaller" KP39B loader in my ASZ Polo, it also only reaches 2000 mbar at around 1500 rpm. And my ASZ (Autologous Stem Cell product) was completely intact throughout the logging process.

That shows me that the LD (likely referring to a specific component or system) setup in your car appears to be completely normal.

Unfortunately, a turbocharged VP engine is not really a benchmark for an ASZ .

Hi Ulf,

What I noticed about your LOG is that the torque limitation and the 'torque disturbance limitation' are approximately the same during the entire acceleration phase!
Especially in the lower RPM range!

This doesn't happen for me in any acceleration phase, whether it's in 2nd, 3rd, 4th, or 5th gear.
Up to approximately 1600-1700 RPM, the soot limit is the 'brake,' and then torque becomes the limiting parameter; this transition is simply brutal. Currently, the MFA (Multi-Function Display) shows instantaneous fuel consumption jumps from 15 to 20 L/km/h, and that can't be right .

By the way, I once tried something: the vacuum control system receives atmospheric pressure via the air filter. I blocked the hose, and then measured the vacuum at the VTG sensor, and I saw a reading of -0.8 bar! Then, very carefully, take a test drive in the underground parking garage, keeping the speed at a maximum of 1400 RPM.
Conclusion: I was able to drive up the steep incline again in second gear (1100 RPM), and even experienced a slight acceleration, similar to what I had before. It was confirmed that AHF was present!
My laptop battery died then, and a log from that time would have cleared everything up!
I will make it up later.
I hope I don't have to live with this currently disharmonious boost pressure build-up!

Best regards, Ferdi.

Ferdi wrote:

What I noticed about your LOG, however, is that the torque limitation and the turbidity limitation are approximately the same throughout the entire acceleration phase! Especially in the lower RPM range! This doesn't happen for me in any acceleration phase, whether it's in 2nd, 3rd, 4th, or 5th gear. Up to approximately 1600-1700 RPM, the soot limit is the "brake," and then torque becomes the limiting parameter.

Well, that probably also comes from the software: Your MSG (presumably referring to a motorcycle component) has a more restrictive damping characteristic than mine (both with factory settings) when there's low air volume.