VW T4 2.5 TDI ACV engine over-revs during emissions test

Hello again

Unfortunately, I'm having a problem with our 1997 T4 with the ACV engine.
He failed the emissions test.
So, I adjusted the ESP on the quantity control valve to the minimum possible power setting.
The ACV has undergone a VTG conversion with 216 injectors. The injectors are newly refurbished and are original Bosch parts. The fuel quantity control unit is also relatively new, with only 50,000 km on it. The car itself has 650,000 kilometers on it.
After adjusting the ESP, it noticeably reduced the amount of soot. When I then simulated the emissions test, the engine revved significantly above 5000 rpm. Before that, it always idled at 4700 rpm when the car was stationary.
I initially suspected the return springs for the pump pistons and replaced them. When disassembling the high-pressure component, I was surprised by the good condition of the pump. There was hardly any wear visible. I reassembled everything, adjusted it, and the bus is running cleaner than ever. However, he still doesn't want to stop at 4700, but is happily continuing to increase it.
I'm now wondering whether the charging rate on the '97 ACV is controlled by the engine control unit (ECU) or by the pump itself.
I really want to make sure that the emission control system is working properly, because I want to reach 1 million kilometers with the original engine.

What do you mean?

Hi,

The idle speed is usually determined by the control unit, so it's likely something is malfunctioning, probably the metering unit has been adjusted to deliver larger amounts.
It detects relatively small injection quantities when the engine is warm and idling (in reality, more fuel is injected than what is indicated in the diagnostic trouble code).

Quote:

When disassembling the high-pressure component, I was surprised by the good condition of the pump.

The mileage is irrelevant; you haven't looked at the entire pump.

Typically, around 250,000 km, the injection timing adjustment in this type of pump begins to weaken.
You can tell by the fact that when the engine is running at full throttle and around 4000 rpm, the target value for the start of fuel injection can no longer be regulated.
The result is black smoke, even though the fuel injection amount isn't too high; it's simply injected too late.

To improve the exhaust emissions test, I would adjust the threshold setting to 5mg/H at idle (warm engine, no load), which is the normal value.

Rotate the pump timing slightly earlier, aiming for a 2° KW before top dead center (BTDC) injection start value (!). Hopefully, adjusting the pump timing will also bring you closer to the target value at higher engine speeds. Please do not start playing significantly earlier; use the search function or contact us if you have any questions.

Also, make sure the ESP gets enough fuel. The injection start is controlled by the internal pressure of the pump, and the intake, filter, etc., must be clear.

Good luck, Rainer.

Thank you very much, Rainer, for this valuable information!

I will check and adjust everything. What you're saying makes perfect sense. I would also like to buy a new pump, but unfortunately, they are no longer available, and because I've had bad experiences with pump overhauls (resulting in 3 breakdowns!), I will now focus on repairing the fuel injection system myself. Perhaps I can replace some of these parts with new ones.

Most recently, we had a specialist in Austria overhaul the pump, after which the solder joints on the flow control valve gradually started to crack. Fortunately, not in Iceland or at the North Cape, but every time it involves a lot of trouble, because of a so-called "pump expert" who is actually incompetent.

Hi,

Just check if the feathers are okay and if the nozzle isn't clogged. The latter is particularly common when the speed and load are constantly the same (i.e., the injection timing remains constant).

The bearing and sealing of the drive shaft are also critical components for achieving very high mileage, as are the seals themselves.
Otherwise, the pump is robust.

Best regards, Rainer.

Thank you very much! I will do that right away.

There's one more thing I wanted to mention.
Our ACV has been fitted with a front-mounted intercooler.
Could it be realistic that so much oil has accumulated at the bottom of the intercooler that it gets sucked in when driving at full throttle, causing the diesel engine to briefly run uncontrollably? My wife is driving even more slowly than usual these days, given the diesel prices. So, there's plenty of time for oil to accumulate.
I'm going to test this out, running it multiple times in a row until there's no more oil left in the LLK.

Hello,
You can safely disregard your theory about oil being drawn into the intercooler when accelerating at full throttle.
The airflow in the intercooler during an emissions test is only a fraction of what you experience during normal driving under load. The exhaust gas volume without load is far too low to generate the corresponding boost pressure and, consequently, airflow.

3bAFN wrote:

The airflow in the intercooler during the exhaust emission test is a fraction of what you have in normal driving conditions under load.

I highly doubt that. Firstly, the tester is flooring the accelerator, so there's definitely a load, but without the engine being held back, reaching 4700 rpm. Then, it's reasonable to assume that the turbocharger pressure overshoots, as there's a very rapid increase in boost pressure. Okay, so if I have 1.5 bar of pressure at 4700 rpm, then the airflow is definitely not just a fraction of 1.5 bar at 3000 rpm.

dieselschrauber wrote:

Hi, The idle speed is usually determined by the control unit, so it's likely something is malfunctioning, probably the metering unit has been adjusted to deliver larger amounts. It detects relatively small injection quantities when the engine is warm and idling (in reality, more fuel is injected than what is indicated in the diagnostic trouble code). Quote: When disassembling the high-pressure component, I was surprised by the good condition of the pump. The mileage is irrelevant; you haven't looked at the entire pump. Typically, around 250,000 km, the injection timing adjustment in this type of pump begins to weaken. You can tell by the fact that when the engine is running at full throttle and around 4000 rpm, the target value for the start of fuel injection can no longer be regulated. The result is black smoke, even though the fuel injection amount isn't too high; it's simply injected too late. To improve the exhaust emissions test, I would adjust the threshold setting to 5mg/H at idle (warm engine, no load), which is the normal value. Rotate the pump timing slightly earlier, aiming for a 2° KW before top dead center (BTDC) injection start value (!). Hopefully, adjusting the pump timing will also bring you closer to the target value at higher engine speeds. Please do not start playing significantly earlier; use the search function or contact us if you have any questions. Also, make sure the ESP gets enough fuel. The injection start is controlled by the internal pressure of the pump, and the intake, filter, etc., must be clear. Good luck, Rainer

.

Could you please tell me what fuel injection amounts are typically displayed during idle (when the engine is warm)?
hg
Herbert.

Hello Herbert,

Can I tell you in two weeks when the bus with the "Holde" is coming back?