AGR Diagnosis: Troubleshooting & Help Needed

Error description:
After driving for an extended period under partial load conditions (country roads, city traffic), the vehicle emits excessive black smoke when accelerating. This cloud of smoke is not only visible at night in the headlight beam but is also clearly noticeable in the rearview mirror during the day. The problem stops after a certain amount of time under full throttle. When driving with a higher proportion of full load (e.g., highway), nothing unusual is observed, but the issue reappears after prolonged periods of partial load operation.
It has nothing to do with soot deposits; I have done several test drives with comparable vehicles.

Solution: If you disable the EGR system by disconnecting and sealing the vacuum hose, the soot problem completely disappears. However, after a long highway drive (approximately 1000 km), the EGR pipe directly behind the exhaust manifold has now burned through – likely due to increased thermal stress.

Troubleshooting attempts in the workshop:
All the components of the AGR system have already been replaced once (the AGR valve and pressure sensor), but they could still be defective.

Vehicle information:
This is a 2001 BMW 525d (CR) with approximately 50,000 kilometers on the odometer. The EGR valve does not have electronic adjustment feedback and is controlled solely by the pressure sensor.

Does anyone know how the control system interacts with the vacuum system, or how they influence each other? Also, when does the EGR valve open and close under normal operating conditions (at what RPMs or parameters)?
I want to try verifying this with a differential pressure gauge.

I am grateful for any advice!

Mike.

Hello,

Quote:

Solution: If you disable the EGR system by disconnecting and sealing the vacuum hose, the soot problem completely stops. However, after a longer highway drive (approximately 1000 km), the EGR pipe directly behind the exhaust manifold has now burned through - presumably due to increased thermal stress.

no.

The EGR valve only opens under partial load and at idle speed, unless it is stuck .
As soon as you really step on the gas, this thing is going to be too fast. If it's already too fast, then sure, the approval certificate might be invalid, but the engine and the people following you will enjoy it.
The basic principle is the same: https://community.dieselschrauber.org/en/viewtopic.php?t=3095

Best regards, Rainer.

MikeL wrote:

However, after a long highway drive (approximately 1000 km), the EGR pipe directly after the exhaust manifold has now burned through - presumably due to increased thermal stress.

I can't quite understand this: on the one hand, the valve is always closed under high load, and on the other hand, without the EGR system, the exhaust gas temperature is lower. I suspect there might be pre-existing damage causing the smoking when running at full throttle.
You will likely be able to control the EGR valve or pressure converter using an analog multimeter, similar to how it's done with TDI engines. Measuring the pressure at the vacuum actuator while simultaneously measuring the voltage could be interesting. If the electric valve and the actual EGR valve (on the manifold) have already been replaced, perhaps one of the vacuum hoses is blocked, causing the EGR to close with a delay.

"I'm interested in what you said about the burnt-out AGR pipe. How could that happen? The material must be able to withstand the hot exhaust gases, since it's constantly exposed to them. Or are you perhaps referring to a plate that you installed to disable it, which might have burned through?"

@Rainer:
I had already read the explanation of the basic AGR function, thank you.
'When I said 'highway driving,' I didn't mean constant full throttle, so of course I don't know if it would have been too much anyway. But doesn't the valve also open, for example, when you release the accelerator? Then any potential heat buildup would gradually dissipate.'

@Christian:
He doesn't generally produce smoke at full load, but only after a longer period of partial load operation. I suspect that an unusually large amount of soot accumulates in the exhaust system, which is then expelled. I plan to perform pressure measurements (both overpressure and vacuum), and I have already purchased a digital manometer for this purpose. If only I knew at what RPM the valve opens and closes?

Mike.

I'm interested in what you said about the burnt-out EGR pipe. How does that happen? The material should be able to withstand the hot exhaust gases, since they are always present. Or do you mean that perhaps a plate that you installed to disable it has burned through?

The EGR pipe has ridges shortly after the flange – I assume for cooling. And it's broken between those ridges. The pipe then connects to an EGR cooler, which is only installed in the automatic transmission version. The manual versions have a completely normal pipe – without any ridges or a cooler. Therefore, I suspect that the exhaust gases are hotter in the automatic transmission.

To the best of my knowledge, AGR pipes always have ribs – not for cooling purposes, but so that they can be installed at all, as they need to be somewhat flexible.

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

No, they are not generally fitted with ribbed pipes. I saw completely normal pipes (not cooled EGR) throughout a tour of the dealer's yard (ALH, ASV models).

Flexible pipes can break from time to time; it's possible that the damage was caused by vibrations.

@mike

'The noise it makes at partial load sounds to me like a clogged vacuum hose for the EGR valve. That's the typical effect. At partial load, a certain amount of vacuum is built up according to the control signal. When full throttle is applied, the valve should close immediately, but due to the constriction in the hose, the vacuum decreases too slowly -> resulting in noise.'
Was ist passiert, wenn jemand versucht hat, das EGR-Ventil durch Klebstoff oder ähnliches im Schlauch zu blockieren, um es 'unsichtbar' zu machen?

-> Check the hose routing, blow through the hose, and of course, check the control valve. If necessary, apply some force carefully; it might be stuck.

For verification: Disconnect the hose from the can, close the hose, and perform a test run.

CU Gremlin.

Was möglicherweise versucht wurde, war, die Abgasrückführung (AGR) durch Klebstoff oder ähnliches im Schlauch zu blockieren, um sie 'unsichtbar' zu machen?
For verification: Disconnect the hose from the can, close the hose, and perform a test run.


@Gremlin
I sealed the EGR hose with a screw, so it's not an invisible solution. I performed the counter-test as you described. The difference is significant. However, I'm still unclear about where the fault lies in the system. The EGR valve was recently replaced -> the problem and the counter-test remain unchanged.
Unfortunately, it's difficult to access the pressure transducer without a lot of effort, but apparently it was already replaced once at around 20,000 km. Of course, it could also be something in the hose. That's what I want to find out using a pressure gauge.

Hi,

just a heads-up:

When my car was new, it also had a noticeable amount of rust, and everything was perfectly fine with the deactivated EGR system.

The ultimate cause was a leak in the pressure control area! With EGR (Exhaust Gas Recirculation), the engine operates much closer to its soot limit, which is why this issue becomes more apparent. Therefore, it doesn't manifest itself when EGR is not active.

Now, 25,000 km after the repair, the EGR system isn't working properly (I have it activated for legal reasons).

Take a look at that; you might have a leak there too.

Best regards,

January.

MikeL wrote:

Then, any potential heat buildup would also gradually dissipate. @Christian: "This only seems to happen after a period of partial load operation. I suspect that an unusually large amount of soot accumulates in the exhaust system, which is then blown out. I plan to measure the (under-)pressure and have already purchased a digital pressure gauge for this purpose. If only I knew at what RPM the valve opens and closes?"

Hi,
There is no heat buildup; the flexible pipe is located outside of the airflow, so not much hot exhaust gas reaches it. It would be most problematic at full throttle, but in that case, the EGR valve is always closed.
I don't believe in soot buildup. At BAB (German Autobahn) speeds, even under partial load, the exhaust flow is high enough to slowly verschandeln out a clogged exhaust system.
I meant what was written above, just as Gremlin explained it in detail regarding the vacuum hose.
The multimeter must be analog because the solenoid valve (pressure transducer) is likely being pulsed with a signal, similar to how it's done in vehicles from the Volkswagen Group (VAG).
Opening and closing primarily depend on the load, not the speed.

Hello, if your car starts to produce black smoke when running at partial load, it means it's not getting enough air.
If the EGR valve is closed, it won't produce soot, as you mentioned.
It's quite possible, as Jan wrote, that a leak in the boost pressure system is causing the problem.
A clogged air filter could also be a possible cause.
Perhaps you could share the specifications of the turbocharger that's installed in your vehicle.

@ Gremlin

"Funny, I only know this version."


Do you have any pictures of the unedited version?

The file only contains images of ribs.

Sure, I can try. With engines like ALH, ASV, and others, all the components are located in front of the injection pump, underneath the intake manifold. It's very difficult to access them with a camera.

My records also only show rib cages.
the ones without ridges, however, were Dutch (hehe... quite a sentence, click).

CU Gremlin.

Here's another one with an electric storage flap (with ribs at the back).



Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

@ gremlin

My Dutch friend got "ripped off." At least that's something... but honestly, it wouldn't have bothered me at all!