Caddy 1.9 PD BLS: High EGR Rate - Fix It!

Hello,

I'm stuck with the repair of my Caddy. It all started when it failed the emissions test.
When measuring the maximum RPM, it smoked terribly, then stalled, and was very difficult to restart.

"There are no error codes stored in the diagnostic memory. After removing the EGR valve, the channels were partially clogged. After cleaning the intake manifold, the vehicle just barely passed the emissions test. However, a noticeable plume of black smoke is visible in the rearview mirror while driving. A diagnostic log using VCDS revealed a significantly excessive exhaust gas recirculation rate. The target value is 250 mg/h, but the actual value was 520 mg/h with a control value of 100.3%. The control value remains at or above 100% even under full load. At partial load, below 1400 RPM, the rate drops to approximately 35%. When entering a town and lightly accelerating at 55 km/h, the engine starts to jerk violently. The values for the idle speed control then go completely out of range."
Cylinder 1 -2.99, Cylinder 4 +3.01. This error could be caused by a faulty vibration damper (ZMS).
I have already replaced the LMM (mass airflow sensor), the AGR valve (exhaust gas recirculation valve), and the PD wiring harness in the cylinder head. The mileage is 293,000 km. It does not have a DPF (diesel particulate filter). I would like to add the log file, but I'm unable to do so.

Hello,

It looks to me like a combination of a leak in the intake manifold, a faulty mass airflow sensor (MAF), and faulty common rail injectors.
Is the correct mass airflow sensor (MAF) installed, and is it free from dirt or debris?
520mg/H of intake air at idle can actually only be "measured" with dirt from the engine bay, because the engine physically can only draw in less than approximately 480 - 500 mg/H.

Best regards, Rainer.

The evaluation of values for idle speed control is only meaningful when the engine is idling; at higher speeds, the values are normally within the expected range. What are the values when the engine is idling?

The EGR valve is, furthermore, non-functional when the actual value (IST) is above the target value (SOLL), which means that more air mass is entering the intake manifold (measured by the mass airflow sensor, LMM) than it should, because the rest of the air is not passing through the EGR valve.


EDIT: What Rainer pointed out is also an important point. If the mass airflow sensor (MAF) constantly provides excessively high values, the exhaust gas recirculation (EGR) system will open much too far, because the system is supposed to regulate based on the target value. This would also explain the extremely carbon-fouled intake manifolds, because that normally doesn't happen with engines of this generation.

A BLS engine without a DPF?
It appears that the DPF (Diesel Particulate Filter) has been deactivated, and likely the EGR (Exhaust Gas Recirculation) system as well. This would then explain the discrepancies between the desired (target) values and the actual values.

In the Caddy, the BLS was also available from the factory without it, and as is common with models like the Golf 5, it came with a DPF.
It likely has something to do with the registration of passenger cars and trucks.

OK. I didn't know that.

Thank you for your replies. The mass airflow sensor actually came from eBay.
The values for the idle speed control are within the normal range when the engine is idling. I will get a decent mass airflow sensor (MAF sensor) on Monday.

I've been buying mass airflow sensors (MAF sensors) from online marketplaces for several years now, and I've always made sure they were Bosch brand, which have always worked perfectly.

Have you ever adjusted the default setting 003 and checked the values? It should be around 475 mg/H when the system is turned off.

In your log, you didn't record any idle time.
When you release the accelerator, 100% throttle closure is normal, and similarly, 100% throttle opening is normal when you press the accelerator. 100% indicates that the EGR (Exhaust Gas Recirculation) system is deactivated.
It would also be interesting to know the injection quantity.
"Once the injection amount exceeds a certain level, the EGR system is deactivated. In your case, this threshold is likely around 33 mg/hour."

At a brand value of 10.34, you're running at full throttle with an IST value of 990 and an LD of 2080. If you calculate that, you get 988 mg/H.

At 30.31, you have an actual value of 1000 with an LD of 2142, which results in 1017 mg/H when calculated.

40.29, IST 530 LD 1244 results in 590mg/H, which is what it should display.

Now, it's also logging while it's running in LL mode. However, you need to be careful here, because after a certain amount of time, it will turn off the EGR. The target value should be around 240 mg/h, and the actual value is almost identical.

In my opinion, the LMM is fine.

I swapped the LMM (lambda sensor) with a working one. The AGR (exhaust gas recirculation) values are significantly better. I've attached a new log file. I previously thought that 100% open meant fully open.

If the part is smoking when the engine is at 2000 rpm in the second gear and under full throttle, please record the following data: engine speed (RPM), mass airflow (actual), boost pressure (actual), and injection timing (advance) at full throttle between 2000 and 4000 rpm in third gear.

Hello everyone,
"Today, I first checked the compression to rule out any mechanical defects. All cylinders have a compression of 30 bar. I logged the idle speed control during idle, and in the second log, I recorded the full-load values."

Hi,

The file containing the LLR data had zero bytes, so I deleted it. Regarding the other log: It looks normal at first glance, but unfortunately, I can't currently check what values are considered normal for the boost angle. I wouldn't want the engine to be smoking due to some kind of improper modification. The BLS engine produced around 135 horsepower, and a boost angle of 32.6° KW for the 105 horsepower stock configuration is quite high, but it could still be normal.

Best regards, Rainer.

The 32° FD angles are also the same in the original file.

Hello,

The engine is original. Please find attached the log file again, showing the idle speed control data during idle.

Thank you for your efforts.

Hüttenhuber.

Based on the turbocharger pressure and air mass readings, I'm less likely to suspect leaks in the charge air system or issues with the EGR system. It would have to be a very specific and unlikely scenario for exhaust gases to be drawn in through the EGR while a small leak in the charge air hoses or intercooler partially compensates for the readings.
The box or similar device is not connected to the PD units? Also, please check the plausibility of the fuel temperature in the corresponding measurement block.

Best regards, Rainer.

Okay, the AGR (Abgasrückführung) definitely isn't working correctly. As long as it's active, the air mass is kept close to the target value. But as soon as the AGR is deactivated around the 34-second mark, the air mass suddenly fluctuates between 360-440 mg/stroke.

Was replaced the AGR valve: a proper new part, or a used part?