Golf IV GTI TDI 81kW - Poor acceleration

Hi everyone,

First of all, a big compliment to your friendly and competent forum. I have only been a keen reader so far, specifically regarding TDI topics. But now, let's get to my problem.

I've been driving a 1998 Golf IV GTI TDI (81 kW) for 10 weeks. It never really performed that well (subjectively), but I bought it anyway because of the comprehensive warranty.
It reaches a top speed of 198 km/h, but the acceleration is relatively poor (recent inspection). Since I'm on vacation and have nothing else to do, I took it to a dyno with a turbocharger (either for a tuner or the workshop). Here's what came out:

Mmax = 202.6 Nm at n = 2780 RPM (this is where the worm gear comes into play / explains the torque).

Pmot = 80.9 kW at n = 4160 RPM (Matches).

Pmax = 89.2 kW at n = 5070 rpm.

The inspector told me that he had inspected many TDIs before, and that mine needed to go to the workshop.

Okay, let's take it to the workshop.
During the test drive at VW, he said it was actually normal. Then he connected it to the diagnostic tester. Here's what happened:

- No errors in memory.
- Reading measurement block 2: 900/min, 0.0%, 0 1 0, 88.2°C
- Reading measurement block: 10 465 mg/H 938 mbar 948 mbar 0.0%
515 mg/H 938 mbar 1458 mbar 100%
- Read measurement block: 11 900/min 1081 mbar 928 mbar 24%
5100/min 1509 mbar 1479 mbar 57%

He didn't explain much to me about those dates, just that everything was okay.
Conclusion at the VW dealership: 'We could, of course, replace the charger - under insurance,' and he grinned .

What do you think about this? Does the charger work well? What would you recommend? The power curve (horsepower) looks similar to that of a gasoline engine.

Thank you in advance for your answers.

Goodbye Thomas.

..unfortunately, they are worthless without precise measurement conditions.

Hello,

I suspect that the values measured by the diagnostic device were not taken while the engine was running at full throttle and under load. Unfortunately, that doesn't provide much information.
Measure the boost pressure after at least 3 seconds of full throttle while driving in 4th or 5th gear, and at an engine speed above 2000 RPM.
The target and actual values must match, and the resulting boost pressure should be approximately 1 bar. The display on the diagnostic device shows the current air pressure, which is being measured at 1900-2000 mbar.

Next, you should check if the mass airflow sensor measures more than 850mg per cycle when the engine is in the low RPM range and you apply full throttle for at least 3 seconds in 4th or 5th gear. The target value must be reached here; otherwise, the diesel injection amount will be reduced to prevent soot formation.

My question to you: Does the engine produce black smoke in the low RPM range when accelerating fully, or not? If it does produce black smoke, it may indicate a problem. Air leak in the intake system, either due to a leak in the intercooler or the pipes (check the clamps!), or due to a stuck exhaust gas recirculation (EGR) valve that is venting intake air directly into the exhaust.
The EGR valve is relatively easy to remove and check for leaks; please refer to the article on the website that explains how the exhaust gas recirculation system works.
I wouldn't replace the turbocharger just yet, as long as you're not experiencing excessive oil consumption.

Regarding turbocharger boost pressure: upon engine start, the vacuum actuator of the variable turbine geometry (VTG) system is immediately moved to the 'maximum boost pressure' position.
At idle, the adjusting rod between the vacuum actuator and the VTG adjusting lever on the turbocharger must be fully retracted into the actuator.
Really completely at its limit, the lever/rod must not jam. If you now turn off the engine, the adjusting rod must completely slide out of the container. Therefore, the entire space inside the container must be utilized.

Best regards, Rainer.

Hello Thomas,

I assume your engine code is AFN (there's a lot of information available online about problems with this engine, especially from Ulf).

Measurement block 10:

Target values:
850..1050 mg/hour
1700..2250 mBar
100% (accelerator pedal position)

The key point about this group is that the measurement was taken at approximately 3000 RPM, with full throttle in 3rd gear. Otherwise, the values are completely meaningless.

If, despite my doubts given the values, the measurement was indeed performed correctly, it is noticeable that the air mass at idle only differs slightly from that at full load. Furthermore, the boost pressure is far too low. This could indicate a faulty or malfunctioning boost pressure control system.


Measurement block 11.
Target values:
2850..3150 RPM
1900-2000 mBar.
1700..2500 mBar
47.95% duty cycle valve for boost pressure limiting.

Here, you can clearly see that the values were recorded under completely nonsensical conditions (5100 RPM). And again, the question: Was the engine only revved up while stationary, or was it running in 3rd gear? Full throttle?
Unfortunately, these values are not usable.


Were you present when the diagnostic trouble codes were read? (Unfortunately, workshops often tend to "clear" the error codes without properly addressing the underlying issue.)
If not, please have the error memory read again.

Hello,

Thank you all for the quick responses.

Well, the engine was only praised when it was stationary, and I was there (that kind of thing stings a little ). The error memory (as far as I could see) didn't show anything.

'I'll start by checking the starting procedure (as described) and maybe look for a different dealer who performs the measurements under full load.'

I would appreciate any further tips.

PS: Why doesn't one always encounter people as competent as those in this forum at VW?

Bye Thomas.

Hi (I forgot something),

'No, it doesn't really produce any smoke. I only noticed a puff of smoke once, and that was when I was in first gear, at a low RPM (around 1300 RPM), and I had to floor it. I saw the puff in the rearview mirror. Otherwise, I haven't noticed anything. And, as can be seen in the dyno test report, it doesn't really start pulling until 2700 RPM, but even then, it's not very satisfying.' What surprises me is that he reaches the maximum speed, but as described, he drops off too much when going uphill (a relatively steep hill where the speed drops from the maximum to 165-170 km/h - which happens quite quickly).

OK, thanks so much.

Goodbye Thomas.