Rough idle 2.5 V6 TDI BDG

Hello from the far north. After spending X hours researching online, I decided to create my own post, even though it's actually a common problem that never seems to have a solution.

First of all: my wife and I drive identical cars. They are both 2004 3BG Passats, with a BDG engine and automatic transmission, and have similar mileage, around 350,000 kilometers.

Problem:
My wife's Passat is running rough at idle. That is, within a certain temperature range (usually between 45 and 85 degrees Celsius of water temperature), the engine has slight misfires every few seconds. I checked with VCDS and noticed that with every misfire, the injection timing jumps from approximately 2 degrees before top dead center (BTDC) to 7 degrees BTDC.

The engine then briefly "stutters" and then runs smoothly again with the correct fuel injection timing. However, the problem only occurs within a specific temperature range. "So, when starting the engine from cold, it runs smoothly until it reaches a certain temperature. However, after driving for a while and the water temperature reaches around 90 degrees..."

"Then there are no more interruptions. And the problem only occurs when the engine is idling. That is, with the transmission in neutral (N) or park (P). When a gear is engaged, the idle remains stable and without interruptions, even within the problematic temperature range. The same is true when the engine speed is slightly increased. That is, everything is fine from approximately 900 RPM. The error memory is empty! The timing belt is new, and the fuel pump is precisely adjusted. The temperature sensor has also been replaced as a preventative measure. The engine always has full power." Just those occasional idle misfires.

Does anyone happen to have any idea what might be causing this? My Passat is running perfectly fine. Even the software versions of the MSG are identical.

Hello.

Quote:

that with every misfire, the start of injection jumps from approximately 2 degrees after top dead center (n.OT) to 7 degrees after top dead center (n.OT).

A loose timing belt is unlikely, but it should be checked.
The ESP pump control unit itself could be the cause of the problem, as could the needle lift sensor and its wiring (are there any chafed areas?), but if the car is otherwise running normally, I would still start by checking other potential causes.

The injection process can be disrupted if air, instead of diesel fuel, is compressed in the injection lines, as air is much more compressible. It is possible that a small leak could allow a few air bubbles to enter the fuel system while the vehicle is stationary.

Therefore, I would first check all the fuel hoses, valves, and fittings, especially those near the fuel filter.
The backflow from the nozzle holder combinations must also be tight.

Best regards, Rainer.

Thank you for the quick response. As I mentioned, the timing belts are new. Since the problem existed even before the replacement, I would rule that out. The leak sounds plausible. However, I can't understand why it would disappear when shifting into a gear, during cold start, or when the engine reaches 90 degrees. But I will follow the advice and first replace all the coolant hoses, filters, valves, and the copper rings on the connections of the return lines.

Hello,

I'm sorry for being so blunt, but it doesn't matter if he's new; what matters is whether he's relaxed. There are actually people who make mistakes from time to time. Some people never do, and it's always someone else's fault.

You just look at him and you know whether he's relaxed or not. First, as I mentioned, I would check the fuel lines and, in particular, the connections to the diesel filter.

Best regards, Rainer.

Since I replaced the belts myself and double-check my work three times, I can say with almost absolute certainty that the belts are correctly installed and the tension is correct, as is the pump adjustment. Otherwise, I wouldn't have made that statement, but would have followed your suggestion. I'm also quite good at handling those with the hoses.

My assumption regarding the difference in N, P, and engaged gear is that, in the latter case, the load on the transmission is higher, which consequently increases the fuel injection amount at the same engine speed.
According to this, the cause should not be in the transmission, and air in the lines would also be an unlikely cause.
hg
Herbert.

Can "swallowing" be filmed in a meaningful way?

Current score:
"New diesel filter including valve, all oil leak lines replaced, sealing rings on the fuel injectors for the return lines replaced. It runs just as poorly as before, or even worse. My statement that the engine runs normally when a gear is engaged, I now have to revise." It's now running roughly under load, but it runs normally from 900 RPM upwards!

"The injection timing is now almost constantly at approximately 7 degrees after top dead center (TDC), and only occasionally jumps back to 2 degrees after TDC. What's strange is that the valve for injection start is constantly at 100.2%. Even when it briefly jumps to 2 degrees after TDC. It makes absolutely no sense. As mentioned, if you increase the RPM to 900 or higher, the valve also regulates normally." I think the pump probably has some kind of problem.

"The reason why it only happens when idling is a mystery to me. I've also recorded a video." You can clearly see how the engine runs normally when I slightly increase the RPM.

Hello,

Do you have a transparent hose to connect to the ESP to prevent foam or air bubbles?

Does the vehicle achieve its full performance? Okay, for example, 1 km at 180 km/h on the highway?

Please provide a Screenshot of the TDI timing checker, once with a cold engine and once with a warm engine.
Okay, I'm ready. Please provide the German text you want me to translate.

Best regards, Rainer.

No bubbles, foam, or anything like that visible in the hose. Performance is fully present. I can try the TDI timing checker tomorrow. Somehow, the upload process for my video keeps failing every time I try.

Simply don't upload gigabytes of 4K video data; instead, use a sensible, lower resolution. You can adjust this setting on your phone's camera.

The sound is almost more important, because besides a flickering tachometer needle, you'll probably see very little.

Quote:

As a result, the injection timing is now almost constantly at approximately 7 degrees after top dead center (ATDC), and only occasionally jumps back to 2 degrees ATDC. What's strange is that the valve for injection start is constantly at 100.2%. Even when it briefly jumps to 2 degrees ATDC. It makes absolutely no sense. As mentioned, if you increase the RPM to 900 or higher, the valve also regulates normally. I now believe that the pump has some kind of problem. Why is it only happening when I'm idling; that's a mystery to me.

At low engine speed, the internal pressure generated by the vane pump is lower, and is likely insufficient to operate the fuel injector control valve.
Take a look at the "should/is" setting for the injection start.
hg
Herbert.

Yes, the target/actual values are somewhat different. So, could the pump simply be worn out?

The scaled video has a size of 0B. Is it on Dropbox or a similar service? Okay, I'll take a look and see where the problem is.

Pinback wrote:

Yes, the planned/target value and the actual value are somewhat different. So, could the pump simply be worn out?

Therefore, please provide screenshots of the TDI timing checker and the corresponding values.

Mechanical wear and tear on a warm pump won't simply disappear. What changes based on temperature is the small circuit near the diesel filter, which switches depending on the temperature... so there's a reason why I say to replace all the hoses and connectors, including the "Knackfrosch" (presumably a specific part).
and check the seals on the filter.

It might be useful to occasionally perform a full-throttle acceleration in 3rd gear and record the engine speed, fuel injection quantity, and injection timing (target vs. actual) (1200-4000 rpm).

It's also possible that one or more fuel injectors are worn out. This is usually normal after around 250,000 km. The question is whether the wear is significant enough to cause misfires at idle. Take a look at the Mean Effective Pressure (MEP) data with the idle speed control, which shows the differences in fuel injection amounts for each cylinder at a constant crankshaft speed.

Unfortunately, I didn't have much time today to take care of the car, as I always have to go on trips on Sundays. However, I noticed that the car is now emitting more smoke, and the exhaust smells very strong. I was still able to record a video. I started both Passats when they were cold and let them warm up. Apart from the jump in injection timing, the read values are approximately the same.

I will upload the video later. The Wi-Fi on the ferry is terrible.

Hello,

The values for the idle speed control are looking good.

The causes of uneven spray patterns are quite straightforward:
- individual air bubbles in the injection lines.
- Nozzle adjuster/control valve defective.
- Faulty needle lifter.

Given the rather significant deviations, one would expect to find error entries in the engine control unit or the ESP system.

Best regards, Rainer.