AXR Performance Issues After ZKD Replacement

Hello everyone,

I'm new to this forum, but I've actually been using a diagnostic system for a few years now and have occasionally read posts here.
So far, I haven't had any significant problems with the car. Reading posts and technical articles has always been sufficient support for me in answering any questions. My experience working on diesel engines, which I've mainly gained (also due to the car's inconspicuous nature), has primarily been with older tractors.

Currently, I'm experiencing a problem with my vehicle that I'm unable to resolve on my own, which is why I'm deciding to sign up.

Here's a brief description of the vehicle: Volkswagen Golf IV Variant, manufactured in July 2002, engine code AXR, gearbox code EUH.
The engine control unit has had a modified data set for operation with vegetable oil since 2005 (approximately at 50,000 km). In any case, the fuel injection timing map was adjusted (shifted earlier), the exhaust gas recirculation system was modified (with a high target air mass, effectively resulting in zero recirculation), and the coolant temperature sensor characteristic curve was changed (starting at approximately 40°C, it corresponds to the actual value; before that, significantly lower temperatures are indicated, which shifts all temperature-dependent maps accordingly during warm-up).
Regarding the driving behavior and control mechanisms, I have not been able to detect any differences after the dataset was changed, which is why I do not want to pursue further modifications - there are other forums for that.

Regarding the issue:

At the end of February, a free repair shop replaced the head gasket on the vehicle, which had approximately 200,000 km on it. The vehicle had overpressure in the cooling system, resulting in water leakage from the expansion tank. During this repair, the cylinder head was disassembled, machined (specifically, the cylinder surfaces were honed), and reassembled. The PD (common rail) injectors were supposedly sealed and adjusted by VW, and the wiring harness was replaced.
Since the repair, the vehicle has experienced a significant loss of power across the entire RPM range. However, the engine runs smoothly (direct cold start with fuel enrichment, no hesitation, no vibrations, no visible misfires across the entire RPM and load range). The engine control unit (ECU) does not show any error codes. The problem and the tests already performed are largely comparable to this topic.
/viewtopic.php?t=26280

The first workshop (independent) has so far:
- The ZKD (crankshaft position sensor) was replaced again (with a thicker one).
- Field measurements were conducted.
A second workshop (Volkswagen) continues:
- The function of the boost pressure control and the mass airflow sensor were positively tested.
- Basic adjustments were performed on the AGR (Abgasrückführung - exhaust gas recirculation) and turbocharger pressure control systems.
- Checked the valve timing (OK).
- Compression measured (approximately 17 bar, with a difference of 2 bar, which was assessed as borderline).

I have:
- Checked the valve timing according to the instructions from this forum.
--> Within acceptable limits, +/- 3 degrees, indicating no change.
- Checked the settings of the PD elements following instructions from this forum.
--> UT, then open 180 degrees, and it works everywhere.
- Fuel return line disconnected before the diesel filter and held in a container.
--> Bubble-free, clear, consistent stream, fills a 0.4L glass in 30 seconds.
- Refueled after 400 km.
--> The MFA (Multifunction Display) indicates a fuel consumption that is 45% higher than the actual consumption when refueling at night.
- Own measurement test conducted (see attachment).

I have the impression that the injection quantities calculated and displayed by the MSG (presumably a diagnostic tool) do not actually reach the combustion chamber in reality, and this is not just in the area of maximum power, but over a wide range of engine speeds and loads. For example, the power loss is already noticeable during maneuvering at idle speed, where the mass airflow sensor (LMM) and throttle position (TL) are not yet playing a major role. Under load, the fuel consumption display rises rapidly (perhaps too quickly) to values of 4-5 liters per hour, and the engine shuts off just as quickly. Similarly, the car accelerates sluggishly even on the acceleration lane in 3rd gear, where, according to my measurements, the air mass, boost pressure, and injection quantity should be more than sufficient.
Based on these observations, I initially didn't plan to replace any parts in the surrounding area. In my opinion, components like the turbocharger, boost control valve, mass airflow sensor, intercooler, and EGR valve are unlikely to be the cause of the problem.
My next step would be to explore tandem pumps or positive displacement elements, and in a first step, measure the pre-charge pressure of the positive displacement element. However, so far, no workshop has come forward to help with this.

Is there a way to verify the actual amount of fuel injected by the PD injectors?

So far, the electrical control of the PDE (presumably a "Pressure Drop Element" or similar) has also remained completely unclear. Is it possible to get any useful information using a standard multimeter, or is it necessary to use a storage oscilloscope due to the rapid control signals?

Thank you in advance for reading and for your ideas.
Stefan.

Hi,
Look over there, https://community.dieselschrauber.org/en/viewtopic.php?t=4053, the compression value is below the wear limit (19 bar).
Replacing the cylinder head gasket with a thicker one is pointless. It increases the compression gap and leads to poorer combustion.
Your observation regarding the consumption levels and the lack of performance further suggests a fault with the power electronics (PDEs) or the tandem pump.
First, I would investigate the lack of compression. Was it measured according to RLF standards? Please check the intake side, including the shut-off valve, to ensure everything is okay. Were the valves ground and checked for tightness, or were they simply installed?
Your measurements initially suggest a slightly low air intake mass and not particularly high boost pressure.
hg
Herbert.

Hello,

Quote:

The first workshop (independent) has so far: - The ZKD (crankshaft position sensor) was replaced again (with a thicker one).

"Why and what thickness? What was previously/originally installed?"

What is the synchronization angle?

Best regards, Rainer.

Hello,

Thank you for your contributions. I'll try to answer now:

Quote:

First, I would investigate the lack of compression. Was it measured after RLF?

I assume that's the case, since the measurement was performed by a Volkswagen workshop.

Quote:

Check the intake side, including the shut-off valve; is everything okay there?

"Will I be checking the parking brake (electric) this weekend? Shouldn't it be open when it's de-energized?"

Quote:

Were the valves ground and checked for tightness, or were they just installed?

I don't know, I'll ask at the workshop tomorrow.

Quote:

why and what thickness? What was previously/originally installed?

The argument was that, due to the cylinder head design, the gasket needs to be replaced from a single-point gasket to a three-point gasket, otherwise the TL will not function. In my opinion, the performance was the same, but I only had the vehicle with the supposedly too thin gasket for one evening, and I immediately returned it.
I don't know which original brand of gasket was installed.

Quote:

What is the synchronization angle?

At approximately -1.7 °KW, the value fluctuates around 1°.

Best regards,
Stefan.

Hello,

Quote:

The argument was that by designing the cylinder head, the gasket would have to be changed from a one-point seal to a three-point seal, otherwise the TL would not be effective.

Since the planned cylinder head, as the name suggests, is flat, it absolutely doesn't matter in this regard.
The only possible reason would be that the closed valves are located closer to the piston due to the design. However, there's nothing to indicate that new valves or valve seats were used; the "old" ones are likely worn out anyway given the mileage.
And even when installing new ones, you can take that into account during the installation process and avoid having to deal with different types of seals.

A thicker gasket results in poorer/stiffer handling, as long as there is NO boost pressure. However, the effect with the three possible gaskets is so small that no one would notice it.

For heroes like that, you don't need to rely on other things either, such as compression measurements (which are far too low) or the adjustment of the PD elements.
Were the PD elements personally checked and approved by you?
Control question to check understanding: What would happen if you turned the adjustment screw for the PD element in the tilting lever one full rotation?

Are the temperatures in measurement block 7 plausible?

Best regards, Rainer.

Hello.

Quote:

Were the settings of the PD elements personally checked and approved by you?

Yes, according to this guide: /viewtopic.php?t=5408

Quote:

Control question to check understanding: What would happen if you turned the adjustment screw for the PD element in the tilting lever one full rotation?

The piston would collide with the bottom of the high-pressure chamber in the PDE.
In a stationary state, at best, the engine might not be able to turn any further. In operation, the weakest component of the PD drive will fail.

The temperatures in the MWB 7 unit are correct. I had already mentioned the modified characteristic curve of the coolant temperature sensor when I presented the vehicle.

Here's another question. In the "So wird's gemacht" book by H.R. Etzold (6th edition, 2005), on page 173, in the section "Removing and installing the cylinder head - Pump/Nozzle engine":

Quote:

The diesel engine cylinder head must not

be reworked. }
How am I supposed to understand this? Planning seems to be a form of post-processing, which shouldn't be necessary in the first place. So, shouldn't the independent workshop have replaced the cylinder head instead of attempting to repair it?


Best regards,
Stefan

Quote:

The plunger would collide with the bottom of the high-pressure chamber in the PDE. In a stationary state, at best, the engine might not be able to rotate any further. In operation, the weakest component of the PD drive will fail.

The candidate understood.

Is it possible to measure the pressure of the tandem pump? Perhaps the type of fuel used was changed at the same time, meaning a different (more viscous) oil was used?

The Etzold is not bad, but it shouldn't be considered a last resort. I don't see any reason why a small amount of material removal (around 1/10mm) would be a problem, as long as the valves don't collide with the piston.

Best regards, Rainer.

Positive values of 60 or 70 are too high for a PD 1.3. This is especially true for a 1.1. That's too slow. This also fits with that:

Dex wrote:

--> The MFA (Multifunction Display) indicates a fuel consumption that is 45% higher than the actual consumption when refueling at night.

Next, it's necessary to determine whether the engine was running on diesel or biodiesel. Also, it needs to be ascertained whether these values are due to the modified software. If not, then the PDE (pre-injection device) is the cause. The value from cylinder 1 is borderline, while the other three cylinders are within acceptable limits.