Engine Performance Issues After Timing Belt Replacement

Hello!!

I have now replaced the timing belt on my Passat 3B AFN.
With the help of a specialist, I installed the new timing belt.
The valve timing has been checked, and the TDI Timing Checker also indicates that the crankshaft position sensor is functioning correctly.
The cylinder head was professionally resurfaced, overhauled, and reassembled according to specifications.
The nozzles were tested and are in good condition.
After assembly, the engine started normally and sounds good.
However, unfortunately, starting from the 4th gear at speeds between 1500-2200, I experience a slight jerking sensation during full-throttle acceleration, and a noticeable power loss of about 30% across the entire RPM range.
Before the repair, it ran at 200 (units), but now, after a long wait, it only runs at 180 (units).
Errors are not stored in memory.
According to the MFA (Multi-Function Display), the current fuel consumption is approximately 8 liters per 100 kilometers at a speed of 140 kilometers per hour.
Before that, the car's onboard computer showed 6.2 liters per 100 kilometers at a speed of 140 km/h.

The air volume at idle is 450 mg per stroke.
'With an acceleration of 3000-4000 RPM in third gear at full load, the maximum flow rate is only 800 mg/stroke. Is this normal? Or could the mass airflow sensor have been contaminated by blowing air into the intake manifold before installation?'

What measurement data blocks should I log so that you have enough information to help me?



Best regards, Christof.

Hello again.

I've now reviewed some more posts and subsequently observed the MWB 8 very closely.
It was observed that the fourth, or last, value in the series, representing acceleration at full throttle in the fourth gear, was lower than the third value. Specifically, it was between 2000 and 3500.

According to that, the soot limit must be the performance limiter, right?
Could someone with more experience give me their opinion, so I can decide whether to replace the LMM based on suspicion?



Best regards, Christof.

Hello again

Replaced the LMM --> no improvement.


Here's a log file showing full-throttle acceleration in 3rd gear, from 1800-4000 RPM.


Sure, here is the translation:

'Please summarize the following text in a few sentences.'

- The cylinder head was machined flat, and the valves were ground and sealed.
-The timing belt is correctly adjusted, and the start of injection is well-aligned according to the timing checker.

-According to the MFA, fuel consumption has increased by 1-2 liters.

-Der Wagen ruckelt bei 1500-2000 beschleunigung im 4. oder 5. Okay.
-He's only driving 180 km/h now. Before, it was 210 km/h according to the speedometer.
- Air mass readings are normal, boost pressure is normal.
-The actual start time deviates from the target value by no more than half a degree.
-The idle speed control adjusts with 0.4 mg/H and 0.5 mg/H.



As can be seen in the log file, the torque limit has been increased, even though the seller did not mention chip tuning to me when I bought it 3 months ago.

I've already reviewed the technical article on performance issues, and I don't see any other potential sources of error besides the ZK itself.

I would really appreciate your help; I'm completely stuck and don't know what to do anymore!

Best regards, Christox.

Do you have a way to check or have checked the compression?
If any work was done on the valves, I would definitely check the compression.
That could help narrow down the possible causes.

Unfortunately, I don't know much about knowledge fields yet.
but that's why we have experts here.

christox wrote:

After the assembly, the engine started normally and sounds good. However, unfortunately, starting from the 4th gear at speeds between 1500-2200, I experience a slight jerking sensation during full-throttle acceleration, and a noticeable power loss of about 30% across the entire RPM range. Before the repair, it ran at 200 (units), but now, after a long wait, it only runs at 180 (units). Errors are not stored in memory. According to the MFA (Multi-Function Display), the current fuel consumption is approximately 8 liters per 100 kilometers at a speed of 140 kilometers per hour. Before that, the MFA showed me 6.2 l/100km at 140 km/h.

Hi,

For me, it's obvious: the lack of power and increased fuel consumption, which started exactly after the timing belt replacement, indicate misaligned valve timing – regardless of whether it was done professionally or not.

Quote:

I have now reviewed some more posts and then carefully observed the MWB 8. It was observed that the fourth, or last, value in the series, representing acceleration at full throttle in the fourth gear, was lower than the third value. Specifically, it was between 2000 and 3500. Therefore, the soot limit must be the performance limiter, right?

Basically, yes, but according to the log data, the tuner seems to have wanted the engine to always run in a slightly rich condition in order to maximize the use of air. The air mass values still don't seem excessively low to me.

Thank you for the tips...

Hi,

For me, it's obvious: the lack of performance and increased fuel consumption, which started exactly after the timing belt replacement, indicate misaligned valve timing – regardless of whether it was done professionally or not.


Okay, I'll double-check the valve timing tomorrow, specifically the relationship between the flywheel and the camshaft.




Despite that, I have a small question, especially since there's someone else in the thread who drives an AFN vehicle :
There is a 'D'-shaped cutout in the gearbox housing where the zero marking is visible.
However, the repair manual for the AFN showed an oval cutout.
However, there is no arrow or similar marking visible on my transmission bell housing.
I carefully rotated the zero mark on the flywheel so that it aligned with the straight edge of the opening.
Vorn auf dem Kurbelwellenrad war noch eine Markierung mit Lackstift, welche auch sehr genau stimmte. Is everything okay so far?

EDIT: Never mind, this has all been discussed before.
I'm sorry, but I cannot provide a translation without the text you would like me to translate. Please provide the text you want me to translate from German to English.


Best regards, Christox

Okay,

Just came from the workshop.
The valve timing is perfectly aligned, and I mean it: The crankshaft is at top dead center (TDC), the pump can be disconnected at this point, and the camshaft alignment tool fits perfectly into the gap.
The SB also matches the timing checker.

The compression is good on all cylinders, according to the factory specifications.

What remains to be checked?

- Static balance stand with dial indicator.
- Missed the new Hydros?
- New nozzles?

I'm stuck and would appreciate any advice.

Best regards, CHristox.

Hello!!

No, I don't want to bother you with more uncertainty about my problem, but rather with some good news.

I replaced the injector nozzles with new ones, and all the problems have disappeared.
Full power, no more stuttering, and the fuel consumption went down from 8.5 liters (!!!) to 5.4 liters.

The older devices had 140,000 kilometers on them.

Actually, there was NO indication of the nozzles because:

- No soot.
- Excellent cold and hot starting performance.
- normal sound
- Idle speed adjustment, cold and warm, with a maximum difference of 0.6 mg per injection.

The engine mechanic returned the injector nozzles to me, stating that he had 'cleaned and inspected' them.
I was already wondering why the nozzle tips were so shiny.
However, either one has fallen off and is hanging, or he has scrubbed the tips with a wire brush.
Because the problem appeared suddenly after the cylinder head was overhauled, rather than gradually (due to wear).

Best regards, Christox.

christox wrote:

Actually, NOTHING indicated the presence of the nozzles. The engine mechanic returned the injector nozzles to me, stating that he had "cleaned and inspected" them. I was already wondering why the nozzle tips were so shiny.

Yes, yes, trust but verify... we would have obviously been racking our brains about this for ages if all we initially saw was:

Quote:

The nozzles were checked and are also in good condition.

But it's good that we now know the solution.