Fuel Injection Timing Off?

Hello everyone,
First of all, I'd like to praise this website and its owner! I've already learned a lot about TDI here, and I've benefited from many of the tips.
Now, I might have a problem.
I've been driving a Golf VI, manufactured in May 1999, with an 81 kW (AHF) engine and 95,000 km on the odometer for a few months.
Equipped with a list of expected values for my engine from the error database, I decided to playfully check my engine. During this process, I noticed the fuel injection timing. This should (presumably at idle) be between -3 and 2 degrees. However, in measurement block 4, I'm seeing a target value of 1.7 (which seems okay) and an actual value of 2.9-3.1 (which fluctuates). Now I'm wondering if the actual value is too high?
I have also tried to change the timing by adapting it.
'But the only thing that changes is the target value. The actual value continues to fluctuate between 2.9 and 3.1. When I set the adaptation value to the possible minimum, I even received an error message.'
17656 - Injection start control, setpoint difference 35-10 --- Intermittent.

Can someone perhaps tell me what this means?
Could it be that something was misadjusted during the timing belt replacement?

Thank you very much in advance!

Patrick.

Hi.

If the actual start of the injection process cannot be influenced, then either the control system is at its limit, or there is a problem with the adjustment hardware – such as a broken cable, a short circuit, a faulty injector control, or a blocked injector.

It would be interesting to see the duty cycle of the injection control valve; could you please share its values under different operating conditions?

In a less severe case, your pump's timing might be slightly off, which in some partial-load operating conditions can even slightly reduce fuel consumption.

Hi Ulf,
Thank you for your response.

I've also been wondering if the pump might be misconfigured.
But I would have expected it to be slightly too late, because I can adjust the injection start time via adaptation, but only in a later direction, not an earlier one.
When I accelerate, the actual value shifts towards an earlier time, but it is always greater than the target value.
How would a faulty adjustable hardware component manifest itself during normal operation? The car runs well overall, except for a little bit of black smoke when accelerating from low RPMs (which might be normal), subjectively speaking.
You only notice that the engine doesn't always run smoothly when it's idling.
Sometimes it feels like there are glitches, but they are very minor and barely noticeable.
I'll try to log the duty cycle of the injection control valve during a test drive (hopefully I can find the right measurement device).

Greetings from Wuppertal.

Hello,

A list of the measurement data blocks can be found in the error database.

Patrick_S wrote:

I've also been wondering if the pump might not be misconfigured. But I would have expected it to be a little too late, because I can adjust the start of injection via adaptation, but only in a later direction, not in an earlier direction.

Hi.

It's possible that I misinterpreted your information...

However, normally the system is set to idle just before the late ignition timing, so that when the accelerator is pressed, a large adjustment range from the idle speed towards early ignition timing is available.
If the problem were due to premature fuel injection, then, in my opinion, the fuel pump would have to be positioned so late that the engine would be difficult to start and would feel sluggish under full load, or would consume more fuel than normal in the upper partial-load range.

Quote:

When I accelerate, the actual value shifts towards an earlier time, but it is always greater than the target value.

"By 'larger', I'm referring to a value that is 'earlier' than the target value. This is usually only possible if the initial setting is too early, or if there's a mechanical defect in the injection adjustment."

Quote:

How would a defective adjustable hardware component manifest itself during normal operation?

Anyway... power loss, misfires, fluctuations in power delivery and engine noise, even with a steady throttle.

Hello Patrick,

What are the actual values at full load and approximately 3500 RPM?
The fuel injection start is controlled hydraulically. Possible causes for the "inability to adjust the fuel injection start" might be, in my opinion, an old (clogged) diesel filter, air in the fuel being drawn in, or debris/dirt on the fuel injection start solenoid valve.
Let's rule out the two most likely and simplest causes of the problem first.

Best regards, Rainer.

Hello everyone,

First of all, thank you very much for your help.


I once took a (unfortunately very short) test drive and logged the data from measurement block 4.
Unfortunately, I'm not yet clear about the values and their interpretation.
When idling, the target value is ,7° and the actual value is +3°.
I always thought that positive values after OT meant it was 'too late,' and that's why I talked about it that way.
When I accelerate, the values decrease and go into the negative range.
'By saying 'the actual value is greater,' I meant that the numerical value is larger, and therefore I thought that the injection start was too late.'
The duty cycle (field 4) is approximately 3% when idling.
When I accelerate, the value increases from a certain RPM.
I've always thought it like this: the system is set to its maximum limit and tries to adjust towards a retarded timing in idle, which is why it has a duty cycle of 3% (no control voltage). When I give it gas, the pump then (because the fuel distributor is closed) quickly moves towards an advanced timing and eventually 'overshoots' the target value. Then, the system tries to readjust, and the duty cycle increases.
It's possible that I misinterpreted the numbers and directions!

What do you think of this theory?

Unfortunately, the logged data appears to be somewhat confusing. I created an Excel chart from it, but that actually made it even more confusing.
If I knew how to do it, I would post those things here.
If you'd like to try it out, I can also send you the file via email.


Greetings from Wuppertal.

Hi.

Whether it's negative or positive, etc.:

If you can apply little to full throttle during a drive without the system hitting its limits (I unfortunately don't know the minimum and maximum duty cycle values, but I think a range of 5% to 95% is okay), then the setting is correct.

If a fault occurs, a late-stage fault (occurring with little gas) is less critical because it doesn't consume any power and doesn't increase energy consumption.
If the system operates at full load and reaches its maximum capacity, the injection timing cannot be advanced sufficiently, which can lead to a loss of power and/or increased fuel consumption.

More details can be found in the technical article about setting up the pump.