Stuttering Comprehension Questions - VP37

Hello.


I'm experiencing the problem that Ulf described with my ALH.

/viewtopic.php?t=658&highlight=unstable+idle

I have 3 questions to clarify my understanding.

If I understand correctly, is the engine running too rich? Is the throttle closing too much, or how does a rich mixture occur in a TDI engine?

2. What do these 4mg/mL mean? How can this unit be explained to a regular person?

'I'm planning to have a chip reprogrammed soon. Is it possible to fix the problem by modifying the fuel map in the problematic area during the chip programming?'

I hope you can help me.

Regards,

Paul.

Hi,

1. Your ALH engine doesn't have a throttle body - it's best to read some articles about how the TDI engine works.

2. A stroke is a movement of the piston from top to bottom. "mg" is a unit of weight. Therefore, there is a specific amount that is injected into each cylinder.

3. I would first try to solve the problem and then attempt any optimization or fine-tuning.

Best regards,

Jan.

'The ALH engine has a throttle valve located before the intake manifold, which is operated by vacuum. Otherwise, how could a diesel engine run too rich at idle? It would simply rev up if you injected more fuel than necessary. Therefore, there must be something that restricts the airflow.'

'It's strange, though, that when I lower the value using VAG-COM, the car seems to run better. So, it's injecting more fuel even though the displayed number is lower. I'd like to understand why this is happening.'

'As I understand it, the problem arises due to too much fuel being injected at low RPM. Why should I do anything about it if the fuel injection quantity can be adjusted via software within a certain range? Or am I misunderstanding something?'

edit: By any chance, are you the Jan who used to drive an 86C and was active in the Hamburg 86C forum?

The throttle valve is used solely to provide a slightly more comfortable idling behavior.
(uses less) fuel. This has nothing to do with idle speed. Diesel engines always run with an excess of air.

Hello!

polo2f wrote:

1. The ALH engine has a throttle valve located before the intake manifold, which is operated by vacuum.

No. That's a shut-off valve. It closes when the engine is turned off. This prevents air from being drawn in and compressed as the engine cools down. This prevents the characteristic diesel engine "clunk" or "stutter" that occurs during shutdown. Additionally, the valve provides an extra layer of safety, for example, in the event of oil being drawn in due to a turbocharger failure.

Genuine throttle valves are still relatively rare in TDI engines. In these applications, they are used to increase the exhaust gas recirculation rate.

Quote:

2. It's strange, though, that when I set a lower value using VAG-COM, the car runs better. So, it's being injected with more fuel, even though the displayed number is lower. Therefore, I would like an explanation for this

.

"The number" indicates the amount of fuel injected for each "ignition" at the current displacement of the control element. Adaptation channel 1 establishes the relationship between these two values, similar to a kind of zero reference.
However, when the engine is idling, the injection quantity is not regulated, but rather the idle speed. This means that the injection quantity remains constant. However, by changing the reference point, the displayed value changes. For the EDC (Electronic Diesel Control), the current position of the actuator no longer corresponds to 4mg, but rather 2mg. As soon as the speed control disengages from the idle speed regulation, the quantity regulation becomes active. In this process, the "deviation" changes accordingly. For example, 50% mechanical actuator movement previously corresponded to 30mg. Now, 50% actuator movement corresponds to 25mg. Therefore, the EDC further adjusts the actuator position to achieve its target injection quantity, resulting in a slight increase in power. This adaptation channel is also intended to adjust the tolerances of the actuator to the characteristic curve within the EDC.


"Unfortunately, jerky behavior can have many possible causes. In cases related to the adaptations mentioned above, the cause is often attempts to modify the engine's performance using aftermarket modules or inexpensive tuning devices, which can push the control system to its limits."
In automatic vehicles, the relatively large rotating mass can sometimes cause jolts that, unfortunately, cannot be eliminated.
The remaining causes (wear and tear, tolerance buildup, aging, etc.) are unfortunately unavoidable.

BYE
TDI mechanic.

Hi,

Regarding the shut-off valve, others have already written enough... just observe it while someone else turns off the engine. Also, looking at the control mechanism, you can see that it's only operated in a binary way, meaning either "open" or "closed." When it's "closed," the engine would essentially shut off immediately...

Quote:

edit: By any chance, are you the Jan who used to drive an 86C and was active on the Hamburg 86C forum?

Not quite. I did, in fact, use that forum... with the nickname "Jan6N". I never owned an 86C, but I did have two 6N models, one after the other, both with gasoline engines, before moving on to the 6K (Ibi).

Best regards,

Jan.

It can't possibly run if it's that fat, right?

'What I've noticed is that in my case, the jerking isn't noticeable when accelerating. On the contrary, when I release the clutch, the engine jerks violently, but only while the vehicle is rolling. When I come to a stop, the jerking stops. Could this be related to the distance signal? Overall, the engine doesn't run perfectly smoothly at idle; there are slight vibrations and occasional misfires.'

I've had two instances of an error message in the engine control unit (ECU) memory: 'distance signal too high.' It always happens when I drive the car at full speed on the highway.

Originally, this was an automatic transmission. Now it has a 6-speed manual transmission and 0.205 injectors. However, with 0.184 injectors, the engine still stutters just as much as it does with the 0.205 injectors. The 11mm pistons from the automatic transmission have been retained.

Hi.

There isn't a true equivalent of "rich" and "lean" mixtures, as used for gasoline engines, in diesel engines.

These are terms from the world of gasoline engines, such as "carburetor" and "spark plugs."

A diesel engine always has too much air (when operated as intended), so it essentially always runs "too lean" in terms of the air-fuel mixture, similar to how a gasoline engine would run.
(He only lacks air if you overdo the tuning or if something is broken, and then he'll sputter and make a lot of noise.)

Here's a simplified version:
Just because a complete, combustible mixture doesn't need to ignite, the combustion process in the cylinder begins (it ignites directly at the nozzle, where the diesel fuel comes out).


When a small amount of diesel is injected (4mg/H is a small amount), there is little power, resulting in low engine speed. If more diesel is injected, there is more pressure on the piston, which usually manifests as higher engine speed.


Gasoline engines are quality-controlled (the air-fuel mixture is adjusted for richness or leanness), while diesel engines are quantity-controlled (the amount of diesel fuel is adjusted, with an arbitrary amount of air).

m;

Edits to ensure that Ulf's post doesn't appear to contradict mine.

polo2f wrote:

If it's too thick, it might not work, right?

You haven't understood the diesel principle yet, have you?
"Too rich" in a diesel engine means soot, soot, and more soot. }

I already understand the basic principle of a diesel engine. I know that diesel engines almost always operate with an excess of air.

I didn't understand your post about VP37. Could you please explain to me, in simple terms, why this jerking occurs? From your post, I understand that you're suggesting shifting the characteristic curve towards 'lower' values. To me, that means reducing the injection amount in all areas. Logically, there must have been more diesel injected than necessary before. Whether it's considered 'rich' or not is ultimately irrelevant. We can call it 'excessive' or whatever. Am I misunderstanding something?

polo2f wrote:

Please explain to me, in simple terms, why this stuttering is happening?

"For simpletons," unfortunately, I don't think I can adequately explain the problem; it remains somewhat complicated.
It's mainly related to wear and tear, and probably also to the transition from speed control to quantity control, as you can also see in the post by tdi-schrauber.

What happens in the engine control unit if I mess around with channel 1? Will the injection times be shortened?

polo2f wrote:

What happens in the engine control unit if I fiddle with channel 1?

Are the injection times shortened?
The articles provide answers to so many questions...
Okay, I'm ready. Please provide the German text you want me to translate.

The pump and the nozzles have a fixed flow rate, meaning a specific volume per unit of time.

We can consider the volume to be equivalent to the mass, so we have a constant, continuous mass flow.

So, if you shorten the injection duration, you inject less diesel.

Since the motor is controlled in that way, does that mean you only have an idle speed of 500 RPM?

So, your assumption cannot be correct!


You are shifting a characteristic curve that acts as an interpretation between the "real world" and the "belief of the control unit." You are NOT shifting the real world itself.

The motor always runs at 900 RPM (under no load), consuming approximately 6 mg/H.
Depending on the characteristic curve position, the control unit believes it is either 2 mg or, with a different characteristic curve position, 10 mg/H.

And it ADJUSTS based on the perceived values. Therefore, does anything actually change about the stuttering if you shift the line?

If you adjust them so that the idle speed (controlled by engine speed) is reached with 1.4 mg/hour, it even stutters at idle because the control system cannot operate with such fine decimal values as required by the assumed injection amounts.



Okay, I can't explain it any better than that, especially if you don't care about technical terms.

We can't just start calling people who can have children "men," because it's just a name!

m;

@Dieselmartin: That's exactly the kind of explanation I was looking for. It's already helpful.

The problem mainly occurs when the engine is idling. Is it due to the large injectors and pump, or could there be other causes? As a temporary measure for testing, I could install the older 0.158 automatic injectors. However, switching to the 0.184 injectors hasn't made much of a difference.

What is the relationship between the engine map and the distance traveled? Because as soon as I stop, the shaking stops. Then you only notice a slight instability at idle.

It's not irrelevant, but you also don't have to overthink everything. I 'grew up' with Otto engines, which don't make assumptions or believe anything without proof. That's why I wanted an explanation. This is important to me because I'm having the chip modified, and I need to explain to the person doing the modification exactly what the problem is, so they can fix it.

The jerking or shaking that occurred while the vehicle was in motion was a common issue with PD engines.
EDIT: I seem to recall hearing something like that.

I've only seen excessive idling on Renault vehicles (specifically, the dCi models, which seem to have this problem frequently) and on TDIs with overly aggressive "chip tuning" (my car and my colleague's ASV model exhibit this behavior with the settings I described, at 1.4 mg/h).

Depending on how your chip is made, it can mess things up in all sorts of ways.

m;