Engine Misfire After Head Replacement - BKD

Good evening, I'm having a small technical issue. It probably belongs in the TDI section, but it's not working for me yet.

"So, I replaced the cylinder head on a 2.0 TDI BKD engine due to a water leak issue. So far, so good. I started the engine, and it initially ran a bit rough, but then it started running normally."
After a 10-15 minute warm-up and bleeding of the cooling system, I took it for a test drive. During acceleration, there was a very strong jerking and loss of power, and the engine shut off. After a lot of cranking and full throttle, it started again, and I was able to limp it back to the workshop.
Connected to port 5052 and found no errors. Idle speed control checked: Cylinder 1: -2 and cylinder 4: +2.8. So, they are compensating for each other. Not ideal. Checked everything again:
Valve timing adjusted, proper seating of the injectors checked, seals replaced again, a different tandem pump installed for testing, the mixing tube in the cylinder head checked for proper seating. The fact is: if I block the return line, the idle speed control returns to the normal range and the engine runs perfectly.

My guess is that the AT cylinder head has a defect somewhere in the channels, causing a loss of pre-injection pressure.

What do you think about it?

Does anyone have any ideas??

Skoda Doc wrote:

My assumption: the AT cylinder head has a defect somewhere in the channels, and the pre-injection pressure is being lost. What do you think about it?

Yes, that seems possible.
The upstream pressure can be measured directly at the pump without significant effort.

"Yes, I have. The pressure is too low. I've already tried all the troubleshooting steps for low pressure. Is there anything else you can think of besides O-rings and the tandem pump? The pre-charge pressure from the pump in the tank is also fine."

Hello, I once wrote an article about this issue, but I can't seem to find it here in the forum right now.

Best regards.

What exactly was that about?

Hello TDI pump injector.
Do you mean this post?: https://community.dieselschrauber.org/en/viewtopic.php?t=3285
Best regards,
Günther

It was about how to test the tandem pump, specifically the pressures and so on.

Okay, I found it. I'll test it out.

Okay, I managed to find a little bit of time yesterday and noticed that the warmer the engine gets, the worse the problem with the jerking becomes. The tandem pump is fine.

Since I didn't modify the cylinder head myself, but a colleague who is currently on vacation did, I need to go through all the possibilities.

Tomorrow, I will expand the PD injectors again and check the seat in the new head. Then, I will install the injectors according to the revised installation instructions (there's even a special video from Audi for it).

"The engineers at VW Audi released these installation instructions specifically to address the poor cold start performance and idling problems in these vehicles. I'm curious to see if it works."

Quote:

The engineers at VW Audi released this installation guide specifically to address the poor cold start performance and idling problems. I'm curious to see if it works.

It wouldn't be bad if you could rephrase the instructions in the form of a post, or is that already available somewhere?

BM wrote:

Quote: The engineers at VW Audi specifically released this installation guide to address the poor cold start behavior and idle problem. I'm curious to see if it works. It wouldn't be bad if you could rephrase the instructions in the form of a post, or is that already available somewhere?

Sure, no problem. It's not much different than usual.

You should now use the tool that was previously used to compress the valve springs and push it into the head, holding it down until the screws are tightened completely.
Apparently, there were many assembly errors because the mechanics installed the pressure differential emitters (PDEs) with screws, which caused them to be misaligned, resulting in a leak between the inlet and outlet.
It's possible that many people already know this, but with Skoda, this kind of information always seems to come out very late. We received a package yesterday with the latest updates (yes, we still don't have ELSA here), and lo and behold, it included the revised installation instructions.

"The engine is running. I removed the injectors again and inspected the sealing surfaces and injector seats. Using the endoscope, I could see small metal shavings on the injector seats in the cylinder head. These likely came from the cylinder head rework. It's already a replacement cylinder head. Additionally, I could see poorly machined fuel channels in 2 cylinders. I then removed the tandem pump and thoroughly flushed and blew out the two fuel lines. Finally, I reinstalled the injectors according to the instructions (although you can skip the step of pressing them down with the valve spring tool) and tightened them correctly."
After bleeding the system with the tester, it then ran perfectly.

Make sure to pay extremely close attention to cleanliness in situations like this. The shavings were barely visible to the naked eye.

Great, thanks for the feedback .