High consumption and Russian education

hello

Hello, I'm actually a mechanic in the T4 Syncro community, but since I've seen that there are very knowledgeable people in this forum, I'm posting about my problem.


I drive a T4 Syncro with a 2.5 TDI ACV engine. The company WKR increased the power by modifying the engine control unit. The vehicle has 33,000 km. There have been no problems since the modification. The fuel consumption was 9-10 liters per 100 km with a spirited driving style.

'However, the fuel consumption is now over 13 liters, and there is a lot of soot buildup. I've already replaced the lambda sensor (oxygen sensor) because it was no longer providing consistent readings. There's a noticeable improvement in power delivery, and I also replaced the air filter. The readings are now stable, but sometimes there's a loss of power.'

The funny thing is that the bus, despite its raised suspension and off-road tires, still runs at 160 km/h (according to the speedometer), although sometimes only after a warm-up period. Furthermore, in 'gra' mode, the speed drops by up to 10 km/h when going up a small hill.

Occasionally, the power loss reoccurs, and it's difficult to reach the 130 km/h mark. However, it performs better again up to 160 km/h. Also, noticeable power dips are felt in the lower RPM range, up to 2000 RPM.

What could the problem be? AGR (Exhaust Gas Recirculation), catalytic converter (I had this issue with a Passat once), a cold solder joint in the control unit, are the vacuum hoses okay?

Thank you for your help.

Peter.

Hi Peter,

Have you taken a closer look at the boost pressure? Additionally, I would suggest temporarily disabling the EGR valve. If you have VAG-COM, you can check the function of the EGR valve at idle immediately after starting the engine by examining the mass airflow sensor (MAF) values. The LMM (lambda measurement module) values should be approximately 200 higher in idle mode when the EGR (exhaust gas recirculation) system is deactivated compared to when it is active.

hello

We discussed the idea with the AGR (Agricultural Register) yesterday as well, and I need to look into it. However, if you just disconnect the hose, it will create an error entry in the system.

I actually don't want to completely disable the AGR (selective catalytic reduction) system, because of the higher exhaust temperatures and potential consequences for the turbocharger.

I'll try to do that next week, thanks.

Hopefully, there will be more great ideas like these.

Peter.

Hi Peter,

The main thing is to ensure the correct function of the AGR (Abgasrückführung). In this case, you should not disable the AGR with a piece of metal. Log the LMM (Luftmassenmesser) values while the engine is idling, then disconnect the AGR hose and log the values again. Afterwards, reconnect the hose and compare the values. We've also seen AGR valves here that would get stuck only above a certain temperature.

syncro peter wrote:

We already discussed the idea with the AGR yesterday, I need to look into it, but then again, there's a potential error entry in the memory if you just disconnect the hose.

Hi Peter,

The error message might not be mandatory and could potentially be resolved through adaptation (see the AGR technical article, which I updated today on this topic).

Quote:

I actually don't want to completely disable the AGR (Abgasrückführung), because of the higher exhaust temperatures and potential consequences for the turbo.

In your case, I suspect that the membrane valve is no longer sealing properly. So, if you make it work properly, everything should function again without you having to permanently disable the EGR system.

By the way, the claim about excessively high exhaust temperatures caused by a faulty EGR system is actually a persistent myth... I've revised the technical article accordingly.

Thank you for the responses so far.

We once had exhaust temperature measurements taken at my workplace. I learned and worked in a cylinder honing shop before starting university, and we collaborated with well-known tuners, which is why we sometimes did those measurements. Temperatures up to 150 degrees higher seem not really good for the turbo, especially in the T4, where the ventilation is already poor.

But I'm happy to be educated if someone explains it to me clearly.

Peter.

syncro peter wrote:

We once had the exhaust temperatures measured at our workplace.

They were up to 150 degrees higher, which, in my opinion, is not really good for the turbo, especially in the T4, where the ventilation is already poor.
Hi Peter,

150°C higher EGT just by disconnecting the EGR?
That would be quite something in itself... but how much higher was the exhaust gas temperature (EGT) at full load (without any tuning)?

As long as the partial-load exhaust gas temperature (EGT) remains below the full-load temperature when the exhaust gas recirculation (EGR) system is deactivated, what's the problem?

But I'm happy to be educated if someone explains it to me clearly.

peter


At full load, the EGR valve is closed. In a stock engine (i.e., without any modifications), the EGR system no longer plays a role in exhaust gas temperature.

TUNING, on the other hand, can significantly increase exhaust gas temperature...

Sure, here is the translation of the text from German to English:

'Cu Gremlin'

hello

I recently disabled my EGR valve using a plate and drove part of my usual commute to get a somewhat objective assessment. Some of the problems seem to be resolved. My vehicle now accelerates 'cleanly, like a bus' all the way to its top speed. However, it still feels a bit sluggish in the lower RPM range, up to around 2000 RPM. The soot formation seems to have improved slightly, but not as much as I expected.

For your information, my EGR valve was clean, as was the intake manifold, with no deposits whatsoever.

I'll probably have to take it to a dynamometer. I'll do a test run first, then see what happens. Maybe it's all related to the performance increase. It's from wkr.

The boost pressure is still active, let's see.

I would appreciate any further tips.

Perhaps someone from bt or nbg could help me with diagnostic issues, of course, for a reasonable fee.

Peter.

Enjoy your meal.

I was on the performance test yesterday, and the results were disappointing!

The curves are clean, and the torque and power are good, but it's 15 kW less than it should be (it currently has 87 kW). The boost pressure consistently lags between 0.3 and 0.4 bar, but eventually reaches its target value. The mass airflow sensor (MAF), despite being less than a week old, is already showing values only at the lower end of the range, around 870. For a Syncro, it should be closer to 1000-1200.
Even if the AGR is shut down due to a fault, there is no change.

The error memory is empty.
The fuel consumption is still around 13 liters!

I've already checked everything, but I couldn't find anything, except that the turbo might have too much play in the shaft.

Now you're asking what it could be, and where I should look.

'Thank you.'

Peter.

Have you ever checked out the dynamic spray start feature? It's best to start by logging data using the legendary VAG COM.

Assuming that the static injection start is adjusted so late that the injection start adjuster is already engaged too early in the early stop position, and then a further early adjustment is blocked. Then the power loss would primarily be noticeable in the higher RPM ranges.

Assuming the ignition timing adjuster is stuck in the 'late' position, if the electrical adjustment force becomes particularly high (at high engine speed), it will suddenly release and snap back to the 'early' position. That would explain the lack of power and the soot formation at lower engine speeds.

Pure speculation. 'Please perform a test run and compare the desired and actual injection timing at various engine speeds.'

hello

Thank you for your reply. I've checked everything as mentioned above, and so far, everything seems to be in order, and the values are correct.

'Thank you.'

Peter.

Hi,

It's possible that the intake area between the EGR valve and the engine is clogged with a mixture of oil and soot, which could be causing the engine to struggle to breathe (possibly only in some cylinders).

Okay, good tip from ulf.

Please examine the intake manifold. A small 'dental mirror' (with a telescopic handle and ball joint) and a small flashlight can be very helpful in these situations.

Perhaps the antler is about to have a heart attack?

Here's another tip: Try the 'Hoppeltest' described here. To do this, enter 'Hoppeltest' into the search function. Perhaps a valve is no longer sealing properly.

hello

'My engine only has 30,000 km on it. The intake area around the EGR valve is completely clean; I've already taken everything apart. Is a valve not sealing properly? I can't imagine that it would have burned through and dispersed itself throughout the engine.'


Peter.

Have you already taken the 'Hoppeltest'? (Search function)

Is the exhaust system sealed for some reason? Perhaps parts of the catalytic converter are blocking it? Go ahead and drive without the exhaust.

Or is there something wrong with the charger?

Are all the nozzles set to the same opening pressure?

Best regards,