Cold start problem PD AUY

I'm having the following problem with my Seat Alhambra 1.9 TDI PD, engine code AUY.
(60,000 km):

At low temperatures, around 8 degrees Celsius or below, the vehicle starts with difficulty, misfires several times, then runs very unevenly for about 10 seconds, runs smoothly for approximately 30 seconds, and then starts to run unevenly again (sounding like intermittent misfires).
After some time, the misfires decrease, and when the engine reaches approximately 35 degrees Celsius, it runs perfectly fine. The problem only occurs in the winter. No error was saved.

The following efforts have not yielded any results:

- Spark plugs are new.
- Preheating system checked, all is well.
-Coolant temperature sensor is OK.
-The outdoor temperature sensor is working correctly.
- All fuel injectors replaced.
- Tandem pump replaced.
-Fuel pressure of the pre-lift pump is within normal limits.
- Oil pressure is normal.
-Compression is okay.
-Timing is correct.
-Engine control unit (ECU) has been replaced.
-LMM is okay.

I'm feeling lost and hoping for a success.
Maybe someone has another idea.

Best regards,
Micha

Hi wildboy,

Does the fuel temperature sensor provide accurate readings, and could the engine have been tuned in a way that relies on this sensor?

Hi,
Almost the entire engine was replaced .
A possible approach would be to, with the vehicle cooled down, check the plausibility of all temperature sensors (especially the fuel temperature sensor) using diagnostic software.

Best regards, Andy.

Hi,

The only part in your car that probably hasn't been checked or replaced yet is likely the camshaft position sensor. The distributor rotor, as well as the distributor cap, can also cause such problems in a PD engine.

I once experienced a problem with a Hall sensor in a TSZ-H ignition system where it didn't function correctly at low temperatures. Great mistake !

Okay, so the fuel temperature sensor is working properly.
I've checked all the values provided by the control unit, and I haven't found any deviations.
That's a good idea about the camshaft sensor; I'll check it out right away.

Okay, so I've now replaced the cylinder head with new PD injectors and camshafts.

The result No change.

What does the customer have in their tank?

Did you notice any coolant leaks, even in small amounts?

Is it possible to make a mistake regarding the distance or alignment when installing the crankshaft and camshaft position sensors?

Best regards, Rainer.

Okay, so the customer isn't using biodiesel, and has also filled up at different brand-name gas stations. This hasn't changed the problem. The camshaft sensor isn't the issue. He is only responsible for the startup process.

Hello,

Has the AGR (Abgasrückführung - exhaust gas recirculation) system been temporarily disabled for testing? Perhaps it's malfunctioning at certain temperatures. The LMM (lambda-minus-minus) values at idle can be quickly checked to determine the issue.

Could it be that there are air bubbles in the fuel system, and that's why the engine is initially struggling to start?
Sure, here's the translation:

"For example, due to a defective sealing ring on the diesel filter?"

That reminds me of my post about my 1.4 TDI! It has the exact same problem! I went back to the workshop today. The result: this is a problem with all pump-nozzle diesel engines! You just have to get used to it because there's nothing that can be done! The mechanic told me that they had already discussed this with the manufacturer and that it's absolutely normal! One engine is more susceptible than the other. They even wanted to give it to me in writing!!!
So, as I said, my 1.4 TDI starts very... roughly, with blue smoke, misfires, and all sorts of problems!

That reminds me of my post that I wrote about my 1.4 TDI! It has exactly the same problem! I was at the workshop again today. The result: this is the case with all common rail diesel engines! You have to get used to it because there's nothing you can do about it! The master mechanic told me that they had already spoken to the manufacturer about it, and that it is absolutely normal! One engine is more susceptible than the other. They even wanted to give it to me in writing!!!
So, as I said, my 1.4 TDI starts very... roughly, with blue smoke and misfires, and all sorts of problems!

hello,
I wouldn't trust statements like that coming from VW.
I have a 3-cylinder common-rail diesel engine with 90,000 km on it, and it always starts perfectly, even in temperatures below 8°C.
No stuttering or anything like that.
It would be a terrible thing if such a highly intelligent engine control system couldn't start properly, even when it's cold.
greetings

Rainer K. wrote:

What does the customer have in their tank?

Hmm, it's possible that the customer has something viscous in the tank, such as grease, (old) vegetable oil, or something similar, which severely restricts fuel flow, especially in cold conditions.
Does it resolve itself when the engine (and fuel, fuel return) gets warmer?
If there's absolutely nothing strange in the fuel tank, then it's probably not the cause.

Rainer K. wrote:

Have you ever noticed any coolant leaks, even in small amounts?

I once had a gasoline engine where the head gasket was leaking, causing a large amount of coolant to enter the combustion chamber in a short amount of time. Interestingly, this only happened under certain conditions and for very short periods. It then consistently caused the engine to misfire for 1-5 seconds. Otherwise, the engine was running almost normally.

Rainer K. wrote:

Can you make any mistakes regarding the distance during the installation of the camshaft position sensor or the crankshaft position sensor?

Well, the tolerances at the edge of functionality are too small/large, causing component shifts due to heating, which then result in temporarily unusable signals...

Is the power supply to the engine control unit (ECU) okay, and is the ECU itself functioning correctly?
"Fluctuations in the wiring harness that controls the Power Distribution (PD) elements should ideally be detected by the control unit (STG), but who knows what kind of bugs might be lurking in the software..."

Best regards, Rainer.