Boost Pressure Issues: Intermittent Problems?

Hi professional mechanic!

As a complete beginner (but eager to learn), I'm having the following problem:
My Skoda Octavia Combi 4x4, 90HP, TDI occasionally (about once per longer trip) experiences a loss of power. Suddenly, at 130 km/h and 3000 RPM, it cuts out. The error code stored in the diagnostic system is: 'Boost pressure regulation difference sporadically stored.' After a restart, the power is restored until the next drop .
What can be done? Is this also the so-called LMM disease? (Can it be cured?)
Ausserdem ist mir im Motorraum folgendes aufgefallen: recht oben liegt ein kleines Kästchen ca 2mal 3 cm mit einem Stecker, es tickert fleissig vor sich hin(ziemlich laut!). Does it have to be this way?
I hope I haven't asked too many silly questions, and that you will still answer me .

Thank you very much.

hakeye

Hi, what is the exact name of the error? Is it a rule difference that is below or above the threshold?

Perhaps you also have the corresponding error code?
Write something.

Hi.

If increased engine load leads to a sudden loss of power that persists until the next engine start, and the power returns to normal after the next start until the next time the accelerator is fully pressed, it is often due to excessive boost pressure, which causes the engine control unit to enter a limp mode with reduced power.
Your error message is generally appropriate.

The cause is often a difficult-to-adjust variable geometry turbocharger (VTG), and less commonly, problems with the boost pressure solenoid valve. I assume that the 90 hp Octavia has a VTG turbocharger.

It's highly unlikely that the LMM is the cause; it's probably something else causing the problem (if it's malfunctioning).

The ticking sound could potentially be coming from one of the magnetic valves for the VTG (Variable Turbine Geometry) or AGR (Abgasrückführung). If that's the case, it would have three hose connections in addition to the electrical connector.

A leak in the charge air duct or a sticking linkage can cause the error 'Regulation limit exceeded' to be logged in the system.
The limit has been exceeded, which can occur even with stiff rods. It depends on the position where the rod is stuck.
Unfortunately, the 66kW engine doesn't have a variable geometry turbocharger (VTG) but a wastegate turbocharger, which can cause overboost, as explained in other posts.
Check the intercooler piping for leaks (listen for noises). Disconnect and seal the intercooler pipe at the intake manifold (use a cloth or similar; while the engine is running) and also check the wastegate.
That's likely your electrically pneumatic valve (for exhaust gas recirculation, the small black device on the injection manifold).

Not quite...
'There are two such boxes in the 90 hp 1Z engine, one for the EGR system and the other for controlling the wastegate. This is likely what's causing that unsightly ticking sound in the hakeye. I once had the same error code on my 1Z, and after replacing this control valve, the error disappeared. However, it's difficult to measure its functionality; in my case, the resistance and voltage drop were correct, but the valve simply wasn't working properly and was constantly ticking. And the good news is: the valve only cost 25 Deutschmarks, a real bargain compared to the mass airflow sensor.'

Best regards,

Dominique.

wilhelm busch wrote:

. . . Unfortunately, the 66kW engine does not have a VTG turbocharger, but rather a wastegate turbocharger. Which, when overboosted, see other posts.

Are you sure? After all, there are newer 66kW engines with VTG turbochargers, and the ALH engine in the Ibiza definitely has a VTG turbocharger.
And since the Octavia isn't as old a model as, for example, the Golf 3, I initially assumed it had a VTG - because it fits the error pattern so well .

Thank you for your posts!

I'm still struggling with Bohemian villages, but I wanted to check that out!
Unfortunately, my used car warranty is with the Opel dealer .
I think they don't have any checks for the nice 66kW TDI, and they always say it should work again soon. (But it doesn't work!!)
So, I guess I have to keep bothering her until it works again!
'Since the problem only occurs occasionally, I always feel like I'm aging prematurely every time my Skoda 90HP 4x4 accelerates past 190 km/h during a test drive!'
However, during a trip of approximately 300 kilometers, it occurred 3-4 times!
Thank you.
hakeye

Hi.

If you want to know which charger is inside, follow the thin hose from the membrane reservoir on the charger, past the solenoid valve (a small device with an electrical connection and 3 hose connections).

In a wastegate turbocharger setup, the other two hoses connect back to the engine's intake manifold: one terminates in front of the turbocharger, and the other terminates behind it.

In the VTG system, one hose (connected via a T-connector) leads to the air filter housing, while the other leads to the vacuum pump, which also supplies the brake booster.

If you have a VTG, you can read the corresponding descriptions on Rainer's website. Afterwards, you will probably know more than your Opel workshop.

Hello Hakeye,

Please provide the engine codes and the model year.
(You can find the license plate code at the beginning of the service booklet).
Then we'll know exactly what your engine is capable of, or what it isn't.

Hello Michael II!
Okay, the engine code letters are 1U537X, 3Y3YKS, and AGR.

I hope you can help me with this?!

Hello.
hakeye

Hello!

So, the problem (sporadic limp mode) has occurred again. This time, I went directly to the workshop:

In the error memory:

17958 P1550 035
Boost pressure.
Rule difference.
intermittent error

Engine code letters are: 1U537X, 3Y3YKS, AGR.

Skoda Octavia Combi 4x4 TDI, 90 hp, approximately 40,000 km.

The workshop suspects it might be the mass airflow sensor (MAF) and suggests it needs to be tested.
or one of the valves??

Was sagt ihr dazu?? LMM testen lassen? Which valve?

Thank you very much for your help!

hakeye

Hello Hawkeye,

The error usually occurs due to:

- Faulty N75 boost pressure control valve.
- Reversed hose connections, not properly connected, leaking.
- Leak between the turbocharger and the engine (charge air path).
- Turbocharger failure.

Let's have that checked first. Then, you can have the measurement blocks 8, 10, and 11 checked both at idle and under full load. That will immediately show whether the problem is with the mass airflow sensor or something else.

Thank you very much!

Hawkeye.

@hakeye
If you want to reliably reproduce the issue, try keeping the engine at approximately 2000 RPM (where it's producing full boost) for a while while driving uphill. Then, gently increase the throttle and wait, then slightly reduce the throttle (not completely, so that the engine isn't being pushed or running freely). It might then go into limp mode, if it behaves like mine... (which there are reasons to believe it does). Just try it out. In what situations has it gone into limp mode so far?
Oh yeah, the whole thing had to be done in 5th gear. It's also possible in 4th gear, but you'd need a much steeper incline.

Hello... thank you very much for your active participation.
It seems I'm not the only one with this problem!

Okay, so the workshop also looked at the N75 magnetic valve and replaced it. Unfortunately, there's no solution. It's ticking quieter now (subjectively perceived by me), but the TDI is still going into limp mode. Unfortunately, it's not reproducible... sometimes at 120 km/h, sometimes at full throttle going uphill, but also going downhill .
'Another workshop recently replaced the mass airflow sensor (MAF), but it didn't solve the problem. However, it now pulls noticeably better in the higher RPM range, and according to the speedometer, it reaches 190 km/h on a straight road (if it doesn't go into limp mode).'

The hose connections have been checked, and the N75 valve has been replaced and reconnected.

So, what's left then?
Do you have a solution?

Thank you in advance!

Hawkeye.

Hi.

IMO, it's still unclear whether you have a wastegate turbocharger or a variable geometry turbocharger (see my post from May 21st).

Check that, and then we can move on.