VW T4 ACV: Ignition Timing Issues & Fixes

Greetings, friends of fine dust .

It's been a long time since I started my last thread here.
But I'm stuck... I couldn't find anything related to that, even using Google.

Problem: The start date of the funding is fluctuating between "early start" and "late start".
The only problem that might arise is a rhythmic, perceived interruption of a working stroke of a cylinder, occurring approximately every 0.5 seconds, but this is likely just a perceived issue and may not be a real interruption. When the engine is warm, this disappears.

During actuator diagnosis, the injection control valve is activated audibly (engine noise), which suggests that it is likely functioning correctly.

I once took a picture of the TDI-Graph with a cloud.

Thank you in advance for your valued opinion!

Have you ever observed the belt path and tension indicator of the ESP's tensioner pulley while the engine is running?
It's possible that the tensioner roller could occasionally run against its stop due to being overtightened. This often happens when the adjustment roller has been turned too much and the tension hasn't been corrected.

Or, it's also possible that the ESP simply wore out, which is unfortunately not unlikely with 350,000 km.

Thank you for your reply!
I checked both timing belts.
Since I once drove 40,000 km with a broken timing belt tensioner, they are regularly checked.
The ESP timing belt tensioner also runs very smoothly.

Is the fuel injection pump itself properly tightened? Check all (!) screws.

Interesting point! But I can also offer a warning. Recently, I got under a car, left the engine running, and fiddled with the pump.
Absolutely perfect!

NHG could be another option, although I'm not very optimistic about it.

Is the KW center bolt tight?
hg
Herbert.

I don't think it's NHG. It should be in the FS (Fahrzeugschein - vehicle registration document).

Herbert wrote:

Is the truck's central bolt tight?

I need to check to see if I can find anything noteworthy there.
The timing belt was replaced by a professional mechanic 70,000 km ago.
I've experienced the loosening of the crankshaft pulley bolt on my Sharan. Suddenly, it became very difficult to start.
Regarding the T4, I know that's also a topic of discussion.

Thank you for the tip!

I had the pump professionally refurbished and installed by a "VP37 Pro" mechanic, but now the engine runs more unevenly at idle.
After checking the start date of the funding, I realized that it was much too early.
I left the bus there, mentioning that the funding was about to start. It still hasn't started, and it's only happening extremely early. This is incredibly frustrating, and on top of that, I'm now over €1000 poorer!
The fuel temperature sensor doesn't seem to be working either. I can't imagine that the fuel would already be 140 degrees after just 10 minutes of driving.

Hi,

A slight (!) variation in the start of the funding period is normal, but what's shown in the image at the beginning of the topic seems to be much larger, perhaps half or a third.

Wasn't the "Out" screw on the fuel return line of the injection pump replaced with a different one? This is important for the internal pressure of the injection pump.
Air or foam in the diesel fuel can also cause sputtering, as air is much more compressible than fuel. Also, check the clear hose for the fuel return line.

Best regards, Rainer.

The value of 140 is just a raw reading from the sensor and does not represent the actual temperature in °C.
140 corresponds to approximately 50°C in real terms.

Thank you for your responses!

The diesel system is free of air bubbles. That was my initial suspicion back then. What's strange is that normally, when the injection timing varies like this, the error code "Injection timing control difference" is displayed.
The "out" screw was not touched. At least, not by me.
A weak or non-dampening tensioner pulley could also cause such a problem in the T4. I will be replacing the main timing belt soon anyway.
The pump specialist just assured me that he has a pump testing facility and that the pump was working perfectly there. Perhaps it really is the tensioner.
And thank you, TDI-GTI-4-Motion, for the clarification regarding the temperature. 140 degrees would have surprised me, even as an extreme value .

Hi,

Tagessuppe wrote:

The funny thing is that normally, when the start of injection varies like this, the error "Injection start regulation difference" is displayed.

Not necessarily; depending on the control unit (software), the detection of the injection start rule difference is quite rough, or almost non-existent.

Take a look at how much the injection timing jumps in °KW at idle; it might not be as bad as you think. As a precaution, it might be a good idea to double-check that both timing belts are running correctly and that the tensioners are working properly.
And as I mentioned before, please check if the ESP retaining screw on the high-pressure component is still present or loose.

Best regards, Rainer.

Hello Rainer,

There are a total of 2 degrees, within which the start date for funding can fluctuate.
Unfortunately, I can't judge whether that's a lot or a little, but my AFN (presumably referring to a measurement or value) had only moved up and down slightly, perhaps by 0.5 degrees.

Okay, that's too much. I would have expected a little more than what the AFN had, considering the two timing belts. I'm familiar with similar fluctuations from my previous AHF model.

Best regards, Rainer.

Is the FB setpoint constant?
What does the control mechanism for injection timing look like on the valve (at the pump)?
Has the valve been inspected more closely before?
The actuator test performed only indicates that the valve is functioning to some extent, but deviations of +/- 2° would not be detected.
hg
Herbert.