AFN Performance Loss After ZKD Change: Troubleshooting.

Hello,

After an extensive search in the forum, I have read some error messages, but none of them seem to match my specific problem.

At 151,000 km, I had to replace the head gasket on my Passat 3B (manufactured in 1997) because I was losing coolant after driving on the highway (a known issue with AFN engines). At that time, the engine still had its usual power and could easily reach speeds of 190 km/h or more on the highway. The timing belt was also replaced during the head gasket replacement.

After I got the car back, I noticed that it jerks noticeably in the RPM range of 1800 to 2000, and also has very little power when starting (almost like an SDI). Additionally, the top speed on the highway is only about 160 km/h on a straight road, even with a lot of acceleration.

Subsequently, I contacted the workshop. After a day of investigations using diagnostic tools, they informed me that the turbocharger was defective and needed to be replaced following the head gasket replacement.

I can't believe this coincidence, and I hope someone here is more experienced than me and can prevent me from having the same problem after replacing the turbocharger.

Here's a possible translation:

'Just as an FYI, the catalytic converter failed about 5,000 km before the head gasket replacement; I emptied it afterward. Some pieces probably remain stuck in the manifold or exhaust system.'

Thank you for your help in advance.

Hello,

To me, it smells strongly like the valve timing has been altered.
Was wäre, wenn der fuel injection timing wurde nicht präzise justiert, sondern nur grob angepasst, nachdem der cylinder head gasket ausgetauscht wurde? Es ist auch möglich, dass Teile des Katalysators immer noch die Abgase behindern.

Blown head gaskets are not really a common problem for the AFN engine!

However, I also agree with the opinion of my predecessor. But after disassembling the timing chain cover, I would only adjust it using a dial indicator. It's simply much more accurate than dynamic checking!

Regards,

Manuel.

Manuel Thomas wrote:

But after disassembling the cylinder head gasket, I would only adjust it using a dial indicator. It's simply much more accurate than dynamic checking!

I completely disagree. In my opinion, dynamic adjustment is the most accurate method!

Hello,

Thank you for your suggestions. Following your recommendation, I initially discussed this with my workshop. They informed me that they used a template and a set of tools to work on it. They checked all the lines for leaks. No error codes are being displayed. They are convinced that there is a mechanical problem with the turbocharger. Since I don't want to spend around 800 EUR just to get a turbocharger for testing, I went to the 'official' dealership.

The mechanic checked all the lines. The VTG (Variable Turbine Geometry) is operating smoothly. No error codes were found during diagnostics. During a test drive, it was determined that the turbocharger is producing sufficient boost pressure. Air mass and fuel injection are also delivering values within the normal range. Nevertheless, my vehicle still feels like an SDI (direct-injection diesel).

Since I've already invested enough and still haven't found a solution to the problem, I'm wondering which workshop (e.g., an independent diesel engine specialist) in the Märkischer Kreis area would be recommended to diagnose and resolve this issue.

Since everything seems to be fine on the electrical side, I suspect a simple mechanical defect, such as a micro-crack in a hose or something similar. Does anyone have any recommendations?

Whether the EGR valve still closes properly .
But then, wouldn't the air mass also have to fit somehow?

Hello,

Thank you for your suggestions. Following your recommendation, I initially discussed this with my workshop. There, I was told that they used a template and a set of tools.

That doesn't mean anything. Nevertheless, the injection timing is being altered.

Regards,

Manuel.

Yes, that's correct; the start of injection can shift, but it has been adjusted accordingly. The mechanic confirmed that the injection timing has been optimized.

I just took the vehicle for another test drive on the highway. There's a lack of power starting around 3500 RPM. The turbocharger works well up to that point. While stationary, I then squeezed the hose behind the intercooler and tested how it builds pressure based on engine speed: up to about 3500 RPM, a constant increase in pressure is noticeable, but after that, the pressure simply drops off.

@marcb:
So, if I understand correctly, you have been relying on the statements from your workshop that everything possible has been checked and is okay .

(Not only) this forum is full of workshop problems despite the claims that everything is okay.

Apparently, in your case, there's no further progress to be made.

"Trust no one but yourself!" -> Get a VAGCOM diagnostic tool, study relevant articles, install an LDA (Linear Density Airflow sensor), and initially check the fuel pump settings.

If you have reached a point where you can share specific and concrete results of your own , we might be able to help you. At the very least, you will then see your TDI from a completely different perspective .

Hello, thank you, and that's all!

Since I plan to sell the car anyway and will be turning my back on Volkswagen and Audi forever, I certainly have no interest in acquiring any diagnostic tools. After the experiences I've had with VW over the past 15 years, I would have learned nothing if my next vehicle were a VW.

Perhaps one of your contributions might have inadvertently led to a result. Nevertheless, thank you for the well-intentioned advice.

I'm now going to look for a diesel specialist and then I'll permanently get rid of the technology that apparently no one at a VW workshop seems to be able to handle.

Thank you, that concludes the matter for me.

marcB

marcb wrote:

Thank you, that concludes the matter for me.

Hopefully, you won't be jumping from one bad situation into another when switching to other brands...

Hello,

I've noticed that many posts and replies offer helpful information. However, for some, I'm missing the ultimate cause and the solution to the problem. Here's the solution to my problem:

Cause:
During the removal/installation of the cylinder head gasket and/or replacement of the fuel injectors, the needle lift sensor was damaged. After replacing it along with the injectors from a 1Z engine, it runs much smoother and has better acceleration, but still doesn't quite reach its top speed. Tomorrow, we will be replacing the parts with new components designed for an AFN engine.

Solution:
Exchange of NHG and nozzles.

'Thank you!'
marcb

P.S.:
Thank you to everyone who provided assistance and...
... nothing is impossible!

Hi,

Thank you for the feedback. What surprises me is that if the MSTG (Main System Test Gauge) reduces performance due to a faulty NHG (Nitrogen Humidity Generator), there usually should be an error entry. Is there no such entry, or with which diagnostic device was it read out?

Best regards, Rainer.

Hello Rainer,

He stood next to the technician in the workshop at the diagnostic station: no errors were detected (error code = 0)!
The same thing happened at the friendly store!
Apparently, there are still 'mechanical' issues alongside the abundance of electronic information that do not result in protocol error messages. In my opinion, sensors, data, and measurements do not cover the entire spectrum.

marcb

... Testers in the field: Gutermann.

marcb

marcb wrote:

Apparently, there are still "mechanical" issues alongside the abundance of electronic information that do not result in protocol error messages. In my opinion, sensors, data, and measurements do not cover the entire spectrum. marcb

Hmm, yes. But if the engine control unit reduces the fuel injection amount, it must have detected something from the faulty sensor... Hopefully your experience with normal performance isn't just a temporary fluke.

Best regards, Rainer.