Fuel Filter Problem: Strange Phenomenon

Hello!

I have a Passat TDI, year 1995, with 174,000 km, and it has the following problem: For the past few days, the engine has been difficult to start when cold, and it smokes white for the first few seconds. I have checked the timing, etc., and everything seems fine. Just now, I looked inside the fuel filter (after removing the return valve) and noticed that there is no fuel visible in the upper part. I recently replaced the supply line. Could it be that a leak in the valve or the return line is causing the fuel filter to empty overnight (due to the suction effect of the supply line)? Shouldn't it normally be completely full of diesel? Thank you in advance .

Hi,
Have you checked the spark plugs?

Best regards, Rudi.

Hi Rudi!

Thank you for the quick response. Someone from VW also told me that. However, since the TDI can be started directly at moderate temperatures, I find it hard to believe that such a glow plug could heat up within 1-2 seconds (well, maybe it can, otherwise every TDI would smoke during cold starts, right?)? In any case, it seems that these things also glow for the first few minutes in the TDI to reduce emissions. I will try it with Ulf's lamp test.

Best regards, Christian.

Hi,
It's definitely worthwhile to check this, as the control light is not activated during the afterglow phase (which occurs after the engine has already started).
Another indication would be if the 'white smoke' has a strong smell of diesel.

Best regards, Rudi.

Hi!

Okay, so: I tested the glow plugs with a test lamp -> all completely dead!!! But according to the literature (I'm helping myself here), the glow plugs only start to glow at temperatures below zero (-> so no problems with dead glow plugs above zero?)!? However, I've already heard from a few people that this can also happen at 8 degrees Celsius.

Best regards, Christian.

haehnlein wrote:

Okay, so: I tested the glow plugs with a test lamp -> all completely dead!!! But according to the literature (I'm helping myself here), the glow plugs only start to glow at temperatures below zero (-> so no problems with dead glow plugs above zero?)!? However, I've already heard from a few people that this can also happen at 8 degrees Celsius.

Hi.

That in there should be a 0° switch for the candles would be completely new to me. As far as I know, the temperature threshold is monitored by the EDC.

"So, you definitely need to replace the candles before it gets really cold. Otherwise, you'll be stuck with them on a frosty morning..."

I remember that preheating issue from last winter too.

At minus 20 degrees Celsius, it took me about 3 attempts to get the fishing line untangled (I don't even want to talk about the white smoke).

That's when it finally dawned on me that the preheating system might be the problem.
Checked the fuse in the engine compartment -> it seemed to be fine (or at least, I thought it was).
All spark plugs were removed and tested -> they were okay.
(They work great with a charger, so you can see if they're really glowing!)

Finally, I figured out the solution to the puzzle.

Caution: There are 2 (!) fuses on the fuse box in the engine compartment. The one under the transparent part is the wrong one. For the glow plug on the 35i, you need to open the small black box next to it; the correct fuse is inside!!!
It was completely crumbled .

But at least, I managed to start the car at minus 20 degrees Celsius without using the pre-heating function.

Best regards.
David.

'I'm experiencing the same problem with my Passat AFN 110hp, and I still haven't found an explanation for it. I've now ordered new fuel injectors because the car has over 250,000 km on it, and I'm hoping this will resolve the issue.'

My car repair shop suggested that I should drain the fuel filter.

Can someone explain to me how to do this and where I need to do it?

I'm sorry, I don't understand. Can you please rephrase your request?

Hi!

Simply unscrew the drain screw (the white plastic part under the filter) and drain 100 ml of fluid (you may need to remove the valve on top -> this will improve the hydraulics, and then reattach it with a new seal). However, I don't think the problem is there. My car is drawing in some air at night (there's a 2 cm air bubble in the intake hose), even though I've replaced all the hoses and seals. This could also be a problem with cold starts. When the engine is running, the ESP shouldn't be drawing in any air bubbles.

Best regards, Christian.

hello!

I'm having the same problem with the AAT. I've already replaced the valves on the diesel filter, but it hasn't helped. However, my car starts without any problems when it's preheated, i.e., when the temperature is below 8 degrees Celsius and the glow plug light is on.

I also think it's somehow related to the diesel supply, but I can't pinpoint the exact problem.

Best regards, Martin.

But what else could it be? I replaced my injectors today, and the smoking has improved by about 50-70%!
I have to say that I don't own a cat... but every time I...
Okay, here's the translation:

'Just for a moment, when I briefly press the accelerator, white smoke comes out of the exhaust, not black smoke. It only starts to smoke gray when I accelerate more forcefully.'

Could it be that the wool in my group A installation is slowly being pushed outwards, and that deposits are forming in the exhaust pipe, which are then blown out when the exhaust pipe gets warm again?

'Thank you.'

Deposits definitely form in the exhaust system.

During my last vehicle inspection, I noticed it significantly, or rather, the inspector from Dekra did.
I was mostly used to driving in the city before. When he floored the accelerator during the inspection, huge black clumps came out of the exhaust. You could have swept them away with a broom.
He then sent me to the platform first, presumably so I could clear the way for the train.
I then drove about 70 kilometers at full speed, and immediately drove back.
After the service, the exhaust emissions were as good as they've ever been in the 7 years I've owned the car. And that's with a mileage of 200,000 kilometers.

'However, I'm only getting a very small amount of black smoke, and only white or gray smoke for the first 2-3 minutes. This usually happens right after the first 5 gas or shift cycles, and then it stops.'

dummy

I got a tip from Henzo (a pump specialist from fatty-fuels.de) about what the cause might be:
-Shaft seal for VP 37 pump.
This sealing ring seems to occasionally fail, especially with higher mileage. When the car stands overnight, air enters the ESP system through this ring, which then leads to insufficient diesel supply to the combustion chambers during cold starts (-> white smoke). This part is supposed to be easy to replace! I will try it and then report back .

Best regards, Christian.

Do you have a part number for that? Can I do it myself? How much does it cost? Otherwise, I might just buy a VP44 pump. Hehe.

but a great tip!

'Thank you.'

Send me an email!

[email protected]

Okay, so I can't say yet how it works (but it's supposed to be simple) -> I'll remove the ESP unit on Wednesday and then I'll report back!! BOSCH part number for the sealing ring: 2 460 283 001. "In addition, it is necessary to check..."
"whether the radial play of the shaft (less than 0.3 mm) and the surface in the area of the sealing lip are in good condition" (quote from Henzo at fatty-fuels.de).

Best regards, Christian