Ignition timing jumps around at VP37 in VW T4 ACV

Greetings, friends of particulate matter .

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

Problem: The start date of the subsidy is fluctuating between "early start" and "late start."
The only potential issue that might arise is a rhythmic, perceived interruption of the operation of a cylinder, occurring approximately every 0.5 seconds. However, this is likely just a perceived issue and may not actually be a real interruption. When the engine is warm, it goes away.

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 be running at its maximum limit due to being overtightened. This often happens when the adjustment knob has been turned too much and the tension hasn't been corrected.

Or, it's also possible that the ESP simply wore out, which, unfortunately, is 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 properly tightened? Check all (!) screws.

Interesting point! But I can also offer some clarification here. Recently, I got under the car, kept 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.

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'm familiar with the issue of the rear axle nut loosening from my Sharan. It became very difficult to start it suddenly.
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" technician, 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. However, it still hasn't started, and only a very small amount has been released so far. 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 time of the funding is normal, but what's shown in the image at the beginning of the topic is probably much larger, perhaps half or a third.

Wasn't the "Out" screw on the fuel return line of the fuel injection pump replaced with a different one? 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. You can also check the clear hose for the fuel return to see if there's any air present.

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 even back then. The funny thing is, normally when the start of injection varies like that, you would get the error message "Injection start regulation difference."
The Out-screw was not adjusted. At least not from me.
However, in the case of the T4, a worn or non-dampening tensioner pulley could also cause such a problem. I'll 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 ran perfectly there. Perhaps it's really the tension spring.
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, 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 timing difference is quite rough, or may not even be present.

Take a look at how much the start of injection jumps in °KW at idle; it might not be as bad as you think. Just to be on the safe side, 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 side is still in place or loose.

Best regards, Rainer.

Hello Rainer,

There are a total of 2 degrees, and the start date for the funding fluctuates within that range.
Unfortunately, I can't judge whether that's a lot or a little, but my atrial fibrillation (AFib) 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 with the AFN, considering the two timing chains. I'm familiar with fluctuations similar to those mentioned by AFN, also from my previous experience with AHF.

Best regards, Rainer.

Is the FB setpoint constant?
How is the injection start timing controlled at the valve (on 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.