AGR Valve: Engine Stall When Deactivated

Hello,

What experiences have you had with disabling the AGR (Exhaust Gas Recirculation) system by blocking the exhaust gas channel and simultaneously deactivating the pneumatic throttle valve? My question specifically concerns the altered engine shut-off behavior, as the throttle valve normally closes when the engine is turned off, ensuring a 'soft' engine shutdown. Is the difference noticeable? And are there any differences between VE and PD-TDI engines? To what extent could an extreme 'backfiring' of the engine during shutdown cause problems?

Regards,

Sepp.

Hi,

Why would one want to disable the pneumatic intake manifold valve?
I don't believe anyone did that.
That actually has nothing to do with a 'clogged' EGR valve.
Or would you like to remove the entire AGR unit?

Hi Achim,

The throttle valve in the intake manifold is partially closed during EGR operation. This is intended to achieve a higher rate of exhaust gas recirculation by creating a greater vacuum in the intake manifold. However, if the EGR channel is blocked and the intake manifold throttle valve is active, the intake air is throttled, which reduces the cylinder filling. This poorer cylinder filling results in a lower compression end temperature, which degrades the ignition and combustion characteristics in these operating ranges. Therefore, it is advisable to either replace the missing amount of exhaust gas with fresh air (bypass) or to eliminate the intake throttling (deactivate).

Regards,

Sepp.

Slowly, slowly!

which engine are you referring to?

Very few engines have a controlled throttle valve, and the VP-TDI engine certainly does not.
'And in engines with a controlled throttle valve, simply deactivating the EGR system would immediately result in an error code being logged (if the engine control unit doesn't immediately shut down the engine because it's trying to regulate the recirculation rate by closing the throttle valve).'

Setting the shut-off valve leads to a rougher engine shutdown. Sometimes it kicks back forcefully, and sometimes it doesn't.
Furthermore, the oil drain plug provides an extra layer of safety. If the engine were to suck in oil for some reason, you wouldn't be able to stop it without the plug.

CU Gremlin.

Hello,

I tested this on a PD-TDI 85kW model from 2002 (with a water-cooled EGR system), and I tried all the different variations. The most complex, but also the most optimal, solution was to install an air bypass channel: it branches off before the mass airflow sensor (MAF) and connects to the EGR valve, while the exhaust channel is blocked. Basically, I replaced the EGR's exhaust flow with fresh air, while still maintaining all the valve and flap functions.

Regards,

Sepp.

Sepp wrote:

...I tested it on a PD-TDI 85kW model, manufactured in 2002 (with a water-cooled EGR system)...

According to Volkswagen, the first 4-cylinder engine with water-cooled AGR (Abgasrückführung) was the AXR with 74 kW, produced from the MJ 2003 model year. I am not aware of any 85 kW engine with water-cooled AGR (but I am open to being corrected).
In the 3-cylinder engine range, water-cooled EGR systems were already available previously (in the 3L Lupo).

Hello,

It's a Sharan manufactured in 2002, possibly a 2003 model year. I unfortunately don't have the engine code (MKB) available. It has an 85kW PD-TDI engine, already equipped with an AGR cooler, but it's one of the earlier models with a square shape. The newer AGR coolers from the 2003/2004 model years appear to have a round shape, as far as I can tell.

Regards,

Sepp.

According to Volkswagen, the first 4-cylinder engine with water-cooled AGR (Abgasrückführung) was the AXR with 74 kW, produced from the MJ 2003 model year. I am not aware of any 85 kW engine with water-cooled AGR (but I am open to being corrected).
In the 3-cylinder engine range, water-cooled AGR systems were already available previously (e.g., in the 3L Lupo).

for the sake of completeness:

The automatic models have water-cooled EGR systems, like my ALH engine (which also has a fuel cooler).

CU Gremlin.

Gremlin wrote:

The automatic models have water-cooled EGR, like my ALH (which also has a fuel cooler).

Okay, convinced!! Then even the figures from VW themselves are not correct...

Okay, I'm convinced!! Then even the figures from VW themselves are incorrect...

If it's comforting: the Skoda spare parts catalog doesn't know anything about the fuel cooler located on the underbody. It should only be there for the ATD model .

CU Gremlin.

Hey everyone.

May I chime in here and ask for a photo of the (allegedly) electric storage compartment door?

I've only seen pneumatic ones so far, and the catalog also shows that all of them (both the air-operated and the water-cooled EGRs) use the same valve-type EGR unit.

Thank you.
m;

Hello dieselmartin,

I have only seen electrically actuated throttle valves in the intake manifold in the newer SDI models: Golf with AQM and AGP engines, and Polo with ASY engine. However, the A2 with the new 66kW 1.4 PD-TDI engine also has this EOBD-compatible electronic valve.

Regards,

Sepp.

dieselmartin wrote:

... (both the air-cooled and water-cooled EGR systems should have the same valve-type EGR unit)...

They don't. The pneumatic system, which normally controls the shut-off valve, regulates the water cooling of the EGR system; the shut-off valve itself is controlled electrically.

It seems that, once again, a distinction needs to be made between older and newer TDI models.

My ALH engine, for example, has a cooled EGR system, but it's not controlled; it just runs constantly.

These models have the same AGR (Active Grille Release) flap as the others.

CU Gremlin.

Gremlin wrote:

Even there, one probably has to distinguish between old and new TDI engines... My ALH engine, for example, has a cooled EGR system, but it's not controlled; it just runs constantly. These models have the same AGR (Active Grille Release) flap as the others.

... You are absolutely right ...

I dug out the VW documentation for the AXR engine again, and it actually states: "... the first 4-cylinder TDI with controlled water-cooled exhaust gas recirculation..."

... how important such a word can be...

Hello,

Thank you for your contributions and presentations. I'd like to briefly list the known AGR systems here (please correct or supplement me if needed):

1. AGR valve with integrated vacuum control valve, controlled via a solenoid valve.
2. Similar to the first, but additionally featuring a throttle valve in the intake manifold, controlled pneumatically or via an electric actuator.
3. Similar to item 2, but with a water-cooled exhaust pipe leading to the collection manifold.

The main reason for switching to an electronically controlled throttle valve is the requirement for diagnostic capabilities of emission-related components. The electronic throttle valve provides a position feedback signal to the engine control unit, unlike the pneumatic version.
Ob euer Fahrzeug bereits EOBD (Euro OnBoardDiagnose) hat, könnt ihr sogar im Fahrzeugschein nachschauen. Unter Schlüssel-Nr.5 steht dann z.b. D-D/OBD 15.
When deactivating the AGR (Abgasrückführung), I chose the method using the fresh air bypass channel, which keeps all actuators and valves active and avoids any error messages. The 'soft' engine shut-off behavior is also maintained.
Following the excursion into the world of AGR systems, here's the question posed at the beginning again:
What specific experiences have you had with the engine behavior when deactivating the AGR (Abgasrückführung) or the throttle valve?

Regards,

Sepp.