AFN Engine Starting Problems: Troubleshooting Guide

I'm having the following problem with my Audi A4 1.9 TDI (AFN):

The vehicle is a long-distance car with a current mileage of 192,000 km. Between trips, the car sometimes sits idle for 2-4 days.
When I start the engine, it sounds for about 2-3 seconds as if the engine is not being lubricated! At the same time, the tachometer fluctuates between 700-1100 RPM. However, this only happens when the outside temperature is below 5 degrees Celsius.

I use Mobil 0W-40 oil, so I think that the 'liquid' oil has flowed back into the oil pan during standstill, and then needs to be pumped to the bearings.

But what about the speed fluctuation?

Regards,
Manuel.

Hi Manuel,

How exactly does an engine sound when it is not being lubricated ?

Normally, the oil pressure warning light goes out about 1 second after the engine starts, indicating that the engine is being lubricated.
Does it take you longer?

Then, possibly, the oil filter might be faulty. It contains a check valve that prevents all the oil from draining into the pan.

I can't quite figure out what's causing the fluctuating engine speed... Does the machine otherwise behave normally (in terms of power, fuel consumption, and oil consumption)?

Is it possible to log the engine data using VAGCOM? That might provide some clarity.

So, the rattling sound is like what you hear when you start the engine after an oil change. But the oil pressure warning light isn't on.

The problem only occurs when the car has been standing for about 3 days and the outside temperature was below approximately 5 degrees Celsius.

While starting, it emits a blue-gray cloud from the exhaust. Once the engine is running, this cloud is only gray, and it disappears around 50 degrees Celsius coolant temperature.

If you start the car after only one cold night, it behaves normally.

I have negligible oil or coolant consumption.
The diesel consumption is approximately 7.0-7.5 liters, depending on the length of the open highway.

The engine also delivers impressive performance. The top speed is 220 km/h (as indicated on the speedometer), and it accelerates from 80 km/h to 120 km/h in 8 seconds (using an Oberscheider chip).

The oil filter can probably be ruled out, as I recently changed the oil, and it was the same problem before that.

The error memory also doesn't contain any entries!

My question is, could the preheating system for just one cylinder be causing the starting problems? But if that were the case, wouldn't there be an error code stored?

Regards,
Manuel.

Manuel Thomas wrote:

So, the knocking sound is like what you hear when you start the engine after an oil change.

But the oil pressure warning light is not illuminated.

Quote:

Hi Manuel, Then it could possibly be the hydraulic lifters. They can sometimes make a rattling noise, especially after cold starts, before they are completely filled with oil.

My question is, could the glow plug system for just one cylinder be causing the starting difficulties? But then I would have an error code, right?

The heating system is not :monitored in terms of potential error entries.

If one cylinder fails to fire immediately due to a faulty spark plug, the engine will sound uneven. However, the engine speed won't fluctuate "extremely" between 700 and 1100 rpm; the unevenness caused by a completely dead cylinder would be too rapid for that.

Have you frequently used biodiesel? --> Possible deposits in the pump }

Thank you very much for making the effort to help me.

I could have figured out the problem with the lifters myself! Sometimes you're so focused on the details that you miss the bigger picture!

The fluctuation in RPM I described, from 700 to 1100 RPM, was just an extreme example to illustrate the problem. Such a significant fluctuation is rare. Last winter, in the Taunus region, with temperatures of -25 degrees Celsius, it happened after four attempts at preheating.

Normally, as it is now, it only oscillates for about 2-3 seconds between 700-900 RPM.

Sorry, I forgot to mention that in my first post .

I have never used biodiesel. I always fill up at brand-name gas stations.

My engine is a bit peculiar when it comes to diesel quality.

When I fill up at DEA or other similar gas stations, the car runs normally without any excessive smoke.

When I use the good ARAL Superdiesel fuel, I feel like it pulls better in the higher RPM range, but then it smokes like a Polish truck every time I touch the accelerator!

Regards,
Manuel.

Hi,

Here's a tip regarding your phenomenon of engine speed fluctuation after a cold start.
My car is experiencing the exact same problem right now. Like you, the cold start issue only occurs in low temperatures.
It's my fault because I only made a temporary adjustment to the ESP after replacing the timing belt. Please check the injection timing using the instructions on Rainer's website.
Besides that, I also recall the issue with the crankshaft gears – please refer to the search function for more information.

Good luck.

Andy.

Hello,
I would suspect one or more faulty glow plugs.
It happened to me too (with my 1996 Passat AFN).
After replacing the faulty part, everything went back to normal when starting the engine.

Best regards, Albrecht.