AEL: Intermittent Limp Mode - Faulty Pressure Sensor?

Hello!


'For some time now, I've been having a problem:'

When accelerating fully, for example when overtaking, the engine suddenly loses power at around 3500 rpm. Then, you have to let the engine speed drop back to idle, and then it has full power again, as if it briefly goes into a limp mode.
Starting from the third gear and up...

It's the 2.5 TDI with 140 horsepower, model AEL.
chip tuned to 170 horsepower (it's not the chip's fault).
No blue smoke from the rear.
I reach the top speed, but not by using full throttle all the way there .

The charging air cooling system is sealed.
Error code: Intermittent boost pressure regulation difference (or similar).


Before I start replacing parts like crazy:
Could it be the pressure sensor? It costs 80 €. I would rather replace that than the turbo .

What else could it be?

What makes you so sure it's not the tuning...? Any logs?

because the chip has been in there for a long time.
and because I've already reinstalled the original chip, and the problem persists.
and if it was working before, then some part must be broken.

Oh, and a long time ago, the cylinder head was also modified, and there's a 76mm pipe running from the turbo all the way to the back of the car. But that probably shouldn't affect the error.


I think the rev limiter is set too high, and the engine goes into limp mode when it reaches the rev limiter, until it reaches idle speed.

My predecessor, according to his own statements, 'adjusted a screw on the turbo' to make it more powerful , but that was a long time ago.
The problem has only been occurring for about a month.

Could it possibly be the pressure sensor? Mine is located directly behind the mass airflow sensor and even has a pressure accumulator.

Hello,

What is the exact error message?
It's likely that the boost pressure is too HIGH. You need to check the control air hose (overpressure) with the N75 valve and also make sure the wastegate isn't stuck.

The N75 resistor should have a resistance of 20 to 28 ohms; if it doesn't, discard it.
Otherwise, check all the other potential causes, including the connection to the N75 valve, etc.


You have mail.

Ah, thank you very much, Malte!
I will also check the private messages right away!
'Thank you!'

Hello Malte, the N75 resistor has a resistance of 17.2 ohms...
Is this still within the tolerance range of 20-28 ohms, or could it be that certain boost pressure peaks are no longer being regulated?
Thank you!

Okay, I would still consider that acceptable.

Do you have VAG-COM? If there are no obviously damaged hoses, I would suggest performing a test drive with the N75 valve disconnected. During acceleration, the boost pressure should remain very stable at approximately 1500 mBar.

If the pressure is too high, the problem could be with the control air supply, the wastegate might be stuck, the pressure sensor could be faulty, or the N75 valve might be stuck in the closed position. To rule out the last possibility, you can bypass the N75 valve and connect the compressor directly to the pressure sensor.

If the pressure setting is okay at 1500 mbar, then the problem lies with the N75 valve or its electrical connections.

PS: Are you still using a wastegate turbocharger? Because you mentioned something about a pressure accumulator. I've never seen a pressure accumulator used with a wastegate system, and I can't imagine it would make much sense.

@ Malte. That's correct as far as it goes. The pressure reservoir is used for the EGR system and possibly for the air conditioning system.

Okay, so the pressure reservoir, which is a sphere with a diameter of 10cm, connects directly to a hose that, at one end, is located on top of the N75 unit.

I have VCDS (formerly VAG-COM), and also an adapter, but unfortunately, I can't find the stupid driver CD for the adapter anymore.

I have a wastegate loader (unfortunately).

If the pressure is too high, the problem may be with the control air, the wastegate may be stuck, the pressure sensor may be defective, or the N75 valve may be stuck in the closed position. To rule out the last possibility, you can directly connect the compressor side to the pressure sensor.

The hoses are all in good condition, and in very good shape.
How can I connect the pressure sensor directly to the pressure chamber? Can I 'bridge' something at the N75 valve?



What happens if I unplug the cable from the N75? Will the turbo then aggressively overboost without any consideration for potential losses?

Henrik wrote:

so, the pressure reservoir, which is a sphere with a diameter of 10cm, connects directly to a hose that, at one end, is located on top of the N75.

That can't be it; then it must be the exhaust gas recirculation valve (N18).

Quote:

How can I connect the pressure sensor directly to the pressure chamber? Can I "bridge" something at the N75 valve?

Yes, but correctly. Don't connect it to anything related to the ventilation system. You'll have to figure out which hoses they are yourself.

Quote:

What happens if I unplug the cable from the N75? Will the turbo then aggressively overshoot without any regard for losses?

NONSENSE, I already explained what it does and what it's for. Disconnecting that pin has the same effect as bridging the N75. Unless the N75 is stuck in the closed position.

Here's an article that explains how the wastegate system works; take a look at it first.

The WG (wastegate) control system is a cascade control system and consists of a mechanical/pneumatic control loop. It works by using the boost pressure itself as a feedback signal, which acts on the actuator (pressure sensor), which then proportionally opens the wastegate.
The MSG, with the N75 valve as a control element and the LD sensor, is superimposed on this control loop. It acts as an independent controller and, using the N75 valve, reduces the feedback signal of the inner control loop, thereby increasing the boost pressure.

Disconnecting or electrically isolating the N75 valve deactivates the external control loop with the MSG (Motor Speed Governor), allowing only the internal control loop to function. This internal loop is designed to produce approximately 1500 mbar.

I have to apologize.
I didn't measure the N75, but the AGR part. It looks almost the same. That's also why there's the pressure sensor; this unit is located behind the MAF sensor.

By the way, to disconnect the AGR (Abgasrückführung), do I need to block the hose from the strange canister to the control unit, is that correct?

Okay, the N75 sensor is located on the rear firewall, and it has a resistance of 26 ohms. That part seems to be okay.
The wiring around seems to be fine, but unfortunately, I can't see the connection to the wastegate on the turbocharger.

I'm currently in the process of temporarily connecting the boost pressure gauge. Let's see what the boost pressure reads... I'm going to install a T-connector in the hose between the N75 valve and the intercooler connection.

Okay, I found the driver CD for the OBD device.

My main problem: low power. It currently reaches 220 km/h, but it used to be faster (around 240 km/h - according to the speedometer - and overtaking maneuvers were much quicker!).

Side issue: Rare, occurs under full load, brief power drop during acceleration. (But it's rare and difficult to log!)


I logged some values.
Perhaps someone with experience could help me interpret this.
(All values are adjusted via chip to approximately 170 horsepower, and until a few months ago, everything was working perfectly.)

First of all,
MWB 10 boost pressure.

,0.00,782.8,1019,1622,100.0,,,,,,,,,,
,0.58,899.6,1023,1826,100.0,,,,,,,,,,
1.10, 1020.7, 1019, 2040, 100.0, , , , , , , , , , ,
1.74, 1068.3, 1019, 2162, 100.0, , , , , , , , , , ,
2.32, 1020.7, 1019, 2060, 100.0, , , , , , , , , , ,
2.85, 1020.7, 1019, 2030, 100.0, , , , , , , , , , ,
3.44, 1007.7, 1019, 2009, 100.0, , , , , , , , , , ,
4.05, 990.4, 1019, 2009, 100.0, , , , , , , , , , ,

Despite the chip, it only reaches approximately 1 bar of boost pressure between 2000 and 4000 rpm at full load. The standard pressure is 0.9 bar, and I believe the chip should provide more boost (I thought it should be around 1.3 bar).



MWB 10 boost pressure with the N75 sensor disconnected (no error code logged!!!???)

,0.00,553.6,1023,1214,81.6,,,,,,,,,,
,0.56,618.5,1023,1316,100.0,,,,,,,,,,
1.19, 661.7, 1023, 1387, 100.0, , , , , , , , , , ,
1.76, 687.7, 1023, 1448, 100.0, , , , , , , , , , ,
2.30, 718.0, 1019, 1489, 100.0, , , , , , , , , , ,
2.93, 748.2, 1019, 1530, 100.0, , , , , , , , , , ,
3.52, 761.2, 1019, 1561, 100.0, , , , , , , , , , ,
4.05, 778.5, 1019, 1581, 100.0, , , , , , , , , , , ,
4.59, 791.5, 1019, 1581, 100.0, , , , , , , , , , ,
5.22, 782.8, 1019, 1591, 100.0, , , , , , , , , , , ,
5.81, 804.5, 1019, 1612, 100.0, , , , , , , , , , ,
6.35, 834.7, 1019, 1652, 100.0, , , , , , , , , , ,
6.94, 856.4, 1019, 1693, 100.0, , , , , , , , , , ,
7.57, 873.7, 1019, 1724, 100.0, , , , , , , , , , , ,
8.13, 873.7, 1019, 1734, 100.0, , , , , , , , , , ,
8.75, 847.7, 1019, 1714, 100.0, , , , , , , , , , , ,
9.33, 834.7, 1019, 1693, 100.0, , , , , , , , , , ,
9.87, 795.8, 1019, 1673, 98.0, , , , , , , , , , ,

Actually, the N75 should maintain a pressure of 0.5 bar, right? In my case, it's going up to 0.7 bar (possibly due to the chip?).

Problem: The perceived performance is exactly the same with the N75 attached... On my test track, approximately the same speeds were achieved (based on feeling!).
On the contrary, I don't want to claim this, but it felt almost more responsive without the N75...
By the way, the N75 has a resistance of 25 ohms, which should be within acceptable limits according to measurements.



Okay, please provide the text you would like me to translate from German to English.
Air volume log, MWB 003.

,0.00,2916,977.5,1038.0,5.1,,,,,,,,,,
,0.66,3326,1020.7,1033.7,5.1,,,,,,,,,,
1.21, 3823, 929.9, 938.5, 5.1, , , , , , , , , , ,
1.81, 3953, 475.8, 761.2, 5.1, , , , , , , , , , , ,
2.43, 3413, 1102.9, 1007.7, 5.1, , , , , , , , , , ,
2.97, 2959.99, 990.4, 990.4, 5.1, , , , , , , , , , ,
3.55, 3154, 977.5, 968.8, 5.1, , , , , , , , , , , ,
4.17, 3326, 968.8, 986.1, 5.1, , , , , , , , , , , ,
4.75, 3521, 964.5, 973.1, 5.1, , , , , , , , , , ,
5.29, 3715, 942.9, 942.9, 5.1, , , , , , , , , , , ,
5.97, 3910, 921.2, 912.6, 5.1, , , , , , , , , , ,
6.56, 4082, 916.9, 891.0, 5.1, , , , , , , , , , , ,
7.12,4255,916.9,860.7,5.1,,,,,,,,,,
7.74, 4385, 916.9, 834.7, 5.1, , , , , , , , , , , ,
8.30,4385,484.4,726.6,5.1,,,,,,,,,,

Is it okay? / Do you think it's okay?



Hmm, what could it be?
All piping is sealed, with no chafing or holes.
km: 280,000
Could it be the turbo, or what?
I can't check the internal wastegate because I don't have the necessary equipment.


Should I log any other values?

Thank you so much!

Quote:

Actually, the N75 should maintain a pressure of 0.5 bar, right? In my case, it's going up to 0.7 bar (due to a chip?),

It's possible that it's due to the N75 valve being disconnected, which means the EDC (Electronic Diesel Control) is not active, and only a proportional regulator remains. This regulator has a constant control difference. If your "wooden hammer tuning" simply injects more fuel across the board, this could manifest in that way.

Quote:

Problem: The perceived performance is exactly the same with the N75 attached... on my test track, approximately the same speeds were achieved (by feeling!).

Your tuning might actually be really bad. In theory, it should be running rich due to the lower air mass.

Please perform a test run with blocks 3, 8, and 11 over several full-load acceleration tests from approximately 1500 to 4000 RPM, and prepare the data as an Excel file (I assume you have VAG-COM) and post it in the upload area. Then we can proceed.

Okay, you're welcome.
I'll do it today.

The chip actually comes from someone who has always worked on my diesel engine, and I trust him a lot... so it shouldn't be some kind of cheap, low-quality tuning.
I really need to try and find a T-08 Torx screwdriver; then I can install the original chips, which should make troubleshooting more objective.


I'll get in touch when I have the logs!

Hello!

Haqbe has posted three logs here.

'viewtopic.php?p=111923#111923'

ranging from approximately 1500 to 4500 rpm.


'The boost pressure values seem to vary quite a bit, don't they?'

Is the turbocharger simply unable to build up the desired pressure?

Thank you!

Standard error for AEL in this case:
- Rubber seal on the lower part of the intake manifold is torn.
- LD connector for the LD control system on the intake manifold has come loose or is leaking.
- Oil separator on the hose for low-pressure control has disintegrated (plastic).
- LD solenoid valve defective.
- Hose of the LD control system damaged/torn/bitten.
- Pressure vessel, charger/water tank/charger in a bucket.

Best regards, Rainer.