TDI Diesel: Fuel Efficiency and Performance

hi,
I have a Golf TDI with 90 horsepower, manufactured in 1995, and I am very satisfied with the car. I have been driving it for about 150,000 kilometers, and so far I have had no problems with it (except for a faulty water pump).

'However, recently it's started producing smoke. As soon as I give it gas while the engine is idling (increasing the RPMs to 4000) and then release the gas, a thick, black cloud of smoke comes out of the exhaust, which I really don't like.'
The car has so far covered 230,000 kilometers. I haven't noticed any loss of power or increased diesel consumption.

What could it be? I was thinking maybe it's the fuel injectors or glow plugs, or perhaps it's related to the diesel fuel. I'm currently getting my fuel from Aral, which supposedly adds an additive to their winter diesel that prevents the engine from idling too roughly during cold starts.

Thank you in advance for your replies.

Hi!

I have a car that's very similar to yours, and I've been exclusively using ARAL gasoline for several thousand kilometers. However, I haven't noticed any unusual amounts of black smoke coming from the exhaust.

Excessively strong black exhaust smoke could be a sign of injector problems.

Best regards, D.

I can't really imagine that the problem is related to the fuel pump. I've read through some of the posts and I'm suspecting it might be the AGR valve or the solenoid valve. I'll check both of them.

The strange thing is that it doesn't lose any power, and the very strong smoke only appears when you release the throttle from a high RPM.

Thank you for your response.

Armin wrote:

the strange thing is that it doesn't lose any power, and the very strong smoke emission only occurs when you release the gas from a high RPM

.

Hi.

That is, however, strange, because when decelerating with zero throttle from a high RPM, the thrust cutoff should engage, so that only air is pumped through the cylinders - so where should soot be generated in that process?

How long does the smoking last (until what rpm does it decrease)? Does it also happen while driving?

Okay, so I changed my winter tires today and also changed the oil and filter.

'After the oil change, I pressed the accelerator pedal fully and then immediately released it. This caused a large cloud of smoke to appear. Every time I pressed and released the accelerator pedal, the smoke reappeared (the heavy smoke filled the entire interior of my car). I don't know if it happens while driving, as I usually don't rev the engine that high, and I haven't tried it out yet today.'

Sure, here is the translation of the text from German to English:

'Hi Armin'

So, it's like this, I put on my winter tires today and changed the oil and filter.

'After the oil change, I pressed the accelerator pedal fully and then immediately released it. This caused a large cloud of smoke to appear. Every time I pressed and released the accelerator pedal, the smoke reappeared (the heavy smoke filled the entire car). I don't know if it happens while driving, as I usually don't rev the engine that high, and I haven't tried it out yet today.'

hello Armin

Hi Armin,
Basically, when you quickly press the accelerator and then immediately release it, it looks like it's emitting smoke at the moment you release the gas. However, the soot is actually created during the acceleration phase and then comes out of the exhaust pipe with a delay.
To determine this accurately, you should take a test drive and have a second person follow you to see if it's constantly emitting black smoke or not. If you do this at night, you'll be able to see the black smoke in the headlights of the person following you.

Is it black soot, or is it bluish?

Regards,


Eike.

hi eike,
First of all, thank you for your reply.

It's a really thick, black, acrid smoke. And now that you mention it, I've actually noticed smoke coming from the exhaust when accelerating, especially when I see it reflected in the headlights of the car behind me, but I didn't think much of it at the time.

The car runs well and has good pulling power, responds well to the accelerator, and I can easily reach its top speed of 190 km/h.

It's understandable that if there's no gas supply, no diesel will be injected. So, it could very well be due to the injectors, which might not be sealing properly anymore. Alternatively, is there perhaps not enough air available for a verschandeln combustion?

Best regards, Armin.

For those who are interested.

This morning, I warmed up the car and observed the exhaust emissions, but I didn't notice anything unusual.
Then I turned it up to the same setting as yesterday, but there was no more smoke, everything seemed normal.

The car is running and pulling properly, but I still went to my workshop to have the error codes read and get the mechanic's opinion. I could have saved myself the trip. He said there were no error codes stored, and if the smoking stops, everything should be fine. I should just keep an eye on it.
He didn't even come out to take a look at the engine.

On the one hand, I'm glad the car is okay, but on the other hand, I'm curious about what caused it. I can't imagine that it was just a few particles from the catalytic converter that burned, given the amount of smoke.

Well, anyway, he doesn't smoke anymore, so I'm curious to see what else might happen.

Best regards, Armin.

Hi Armin,

If you are also one of those who drive economically, then the airflow in the exhaust system may not be sufficient to remove the soot particles.

I once took my father's car (an Audi 80 TDI 1Z with 95,000 km) for the vehicle inspection (ASU), and the initial emissions test was way beyond acceptable limits. Then, I drove it a few kilometers on the highway, pushing it to full throttle and high RPM ("let it smoke," as the TÜV inspector said), and surprisingly: everything was perfect!!! It turned out that there were deposits in the exhaust system that only dissolved at high RPM.

Best regards, Christian.

Hi!

I already mentioned my last time off in a previous thread.
At first, only a few small pieces came out, the kind you could have swept away with a broom.
After driving at full throttle for 50 kilometers on the highway and then immediately getting a new emissions test, the results were the best they had ever been, and this was at a mileage of 200,000 kilometers.

Best regards, D.

Hey, just thinking about something else now.

I used to own a POLO 86C. At one point, it was leaking some oil from the engine ventilation system because a filter, which separates the ventilation hose from the crankcase, had frozen due to condensation or something similar during the winter. That was at least the explanation given by a mechanic.

How does it work with a TDI engine if it sucks in a charge of oil when it's revving high, and that oil has accumulated somewhere in the intake system (e.g., the intercooler)? Theoretically, it should just burn. But if there isn't enough oxygen available, it's likely to produce a lot of soot.

Regards,

Eike.

hi,

'I've driven 500 km since I started smoking, and I haven't noticed anything unusual, but I think it might be running a little better.'

When I went for the emissions test in August, the technician had to repeat the measurement five times until the values were correct. During the process, small particles came out of the exhaust, and he said it was likely due to driving at low RPMs.

When the smoking started, I had the car positioned on ramps, and I suspect that soot particles, which normally stay in the exhaust system, might have been drawn into the exhaust stream.

I will definitely keep an eye on this. Maybe I'll find a workshop that can read the error codes.

Best regards, Armin.

I can only agree with Haehnlein's opinion.
If a TDI engine is primarily operated in the lower and mid-range of its RPM, the exhaust system will gradually accumulate soot (which all diesel engines produce).
This can lead to a loss of power. Occasionally, letting it run free works wonders. Sometimes, even glowing pieces come out. This causes excitement on the highway.