Engine Misfire at 3000 RPM: Intake Manifold Issue?

Audi 80 Avant, 1.9 TDI engine, 1Z code (202 Nm torque), manufactured in March 1994.

Hello everyone,

2 months ago, I connected an LDA to the hose leading to the MSG (see here), and since yesterday, I've been having a problem with the boost pressure.

The car was running without any problems until yesterday; however, the LDA (Lambda-Sonde) only showed a maximum of 0.5 bar. Yesterday, while driving on the highway in fifth gear at approximately 3000 RPM, it suddenly stopped working completely... and the LDA displayed almost 1.5 bar.

Using the search function, I'm now consistently finding that a stuck VTG (Variable Turbine Geometry) or leaks in the pressure hoses are the causes. I can rule out the VTG on this particular model (1Z), and I haven't found any visibly torn or detached pressure hoses either.

I am encountering the following errors in the MSG:

Quote:

Sunday, May 25, 2008, 19:04:55:13924 VAG-COM Version: RKS 704.1 Address 01: Engine. Control unit part number: 028 906 021 D. Component and/or version: 1.9L R4 EDC SG D21. Encoding: 00000 Workshop Number: WSC 00000 Sure, here is the translation of the text from German to English: "2 errors found:" 00575 - Intake manifold pressure. 17-10 - Rule difference - Intermittent/Sporadic. 00519 - Manifold absolute pressure sensor (G71) 28-10 - Short circuit to positive - Intermittent. Readiness: not available

Does anyone have a good tip on where I can look? I'd rather not open the control unit unnecessarily and would prefer to examine the sensor more closely.

I'm particularly concerned about the "short circuit to positive" – could a cracked or detached pressure hose be the cause?

Thank you and best regards.

Hi,

I believe that error code 00519 is a consequence of error code 00575.
Your wastegate is stuck and not opening (possibly due to rust?). You don't have a variable geometry turbocharger (VTG) in your 1Z engine.
You can easily check the turbocharger pressure sensor in the control unit using VAG-COM. The actual turbocharger pressure value in measurement block 11, minus the ambient air pressure in measurement block 10, should match the value displayed on the turbocharger pressure gauge.
It's also worth checking if anything has been chewed on the relevant hoses. There is a specialized article available about hose installation.

Best regards, Rainer.

Today, I cleaned the oil contamination under the turbocharger and on the magnetic valve (engine cleaning) and took it for a test drive (hopefully, the oil was just from spilled engine oil during filling). The boost pressure mostly matches the display, so I suspect that the previous display, which showed up to 0.6 bar max., may have been stuck due to a jammed needle (the LDA had been stored in the basement for 2 years with oil in the hose).

However, the error occurred twice again during the relatively short highway drive, even though I revved the engine above 4,000 RPM on two occasions. I've attached the log file in case anyone can provide more specific information based on it.

Can I simply remove the wastegate rod with a can and check it, or will that potentially adjust the length and cause even more problems?

Hi Tino,

The problem lies with the chip tuning in your engine control unit. It's not worth anything. No standard 1Z engine has a boost pressure of over 2000 mbar at 4000 rpm.

If you're going to do something, then you should reveal the whole truth. Also, your mass airflow sensor isn't in the best condition; otherwise, it would measure a slightly higher amount of air at a pressure of 2080 mbar and an engine speed of 4000 rpm.

It's possible that these chips don't even belong in this control unit; I've experienced some very strange effects as a result.

Best regards, Rainer.

Chip tuning??? I'm the original owner and I definitely never had the chip tuned - it's completely original! The only "tuning" modifications to the engine are a blanked-off EGR valve (with a metal plate) and larger injectors (AFN). I'll just mention the useless sports air filter and the large exhaust for completeness. However, the MSG (engine control unit) has truly never been touched, especially no chip tuning, not even a minimal "10 Cent" tune.

Do you have a possible explanation for this? The characteristic curve is surely pre-programmed and shouldn't be affected by potentially faulty sensors – at least not to such an extent that it deviates from the norm, right?

Edit: I will spray the mass airflow sensor (MAF) with brake cleaner again; it might indeed be a bit dirty. However, I wouldn't consider it the primary suspect right now, especially if the pressure setpoints are incorrect.

Could the label file for VAG-Com potentially be incorrect? I'm wondering if I might have replaced it with a German one (hopefully not an incorrect one)? However, "label" files only provide labels and don't alter the channels... mmmhhhh - that was just an idea.

Okay, >2000mbar of boost pressure at 4000rpm is _not_ standard for the 1Z engine. The VAG part number is in the log file, so I'll quickly find out what the standard boost pressure is.

So, with the part number 028906021D D21, I achieve a boost pressure of 1800 mbar at 4000 rpm and 1900 mbar at 2000 rpm. Now, here's the question: how does your STG (Steuergerät - control unit) reach 2007 mbar?

If that's always been the case, then something has always been wrong... it wouldn't surprise me if things get bumpy.

And if you happen to take apart such an engine control unit and look closely, it becomes clear where the

Quote:

00519 - intake manifold pressure sensor (G71) comes from. 28-10 - Short circuit after positive voltage - Occurs sporadically

. In that case, the system has been tuned from a load pressure regulation to a negative control.

If you've been barely managing to achieve the desired boost pressure so far, it might be due to a now-failing N75 valve.

Best regards, Rainer.

I'll probably replace the N75 as a precaution and also renew those slightly more expensive hoses.

I still can't understand where the higher target pressure is supposed to be coming from! No one other than Audi and me has messed with the car, and nothing was actually done to the chip. I've always wanted to address this and have the chip adjusted to match the injectors, but that hasn't happened yet. And I don't think I'm a second Uri Geller who can tune his chip with his mind .

Hello Tino,

kann es sein, daß Dein Umgebungsdruck (Umgebungsluftdruck) unplausibel hoch ist? Wird in Meßwertblock 10 als 2. Wdisplayed.
At what altitude do you live?

Best regards, Rainer.

I live in a small apartment of just 53 square meters, located on the other side of the Rhine River from Bonn. However, yesterday it was very humid in the Cologne/Bonn area, which could have resulted in increased air pressure.

I will test this again tonight (if I have time). That would probably explain the added turbo boost pressure.

Wo liegt der Sensor für den Umgebungsdruck? Den würde ich mir dann auch mal genauer angucken. ADo you also use MSG?

The magnetic solenoid valve and its hoses have just been ordered.

Hi Tino,

Quote:

I will test this again tonight (if I have time). That would then probably be an explanation for the added turbo boost pressure.

Okay.

Quote:

Where is the sensor for ambient pressure located? I'd like to take a closer look at it. Is it also in the MSG?

Yes, but you can't really do much testing there; you can only check if the ambient air pressure seems reasonable.

Before we start speculating too much here, the simplest solution would be to replace the N75 component.

Best regards, Rainer.

Okay, the measured ambient pressure is perfectly fine – today it was just under 1000 millibars, which is very realistic. With the engine off, turning on the ignition even shows exactly the same value for both ambient and boost pressure – as it should.

"During today's test drive (despite heavy traffic), I was able to reproduce the problem twice (including an error code being logged) under full throttle – see the log file (which includes a timestamp). However, based on my understanding, the values appear to be fine, including the target pressure. The air mass, however, seems suspiciously constant."

As I mentioned: The N75 valve and the corresponding hoses will definitely be replaced. However, something else caught my attention today (after yesterday's engine cleaning):

I've found oil again underneath the turbocharger (I suspect "again," since it was cleaned quite thoroughly yesterday). Could this be due to a leak in a hose, or shouldn't there be any oil leaking even if there *is* a hole? I'm now worried about potential bearing damage inside the turbocharger.

That's it!!!

Yesterday I replaced the N75 valve and the three hoses... today I took it for a longer test drive... everything is fine! For those who are interested, I've attached a log file from today for comparison.

It is noticeable that the actual and desired air pressure are relatively very similar , however, the actual air mass is too low compared to the desired value .

Command retracted .

After a trouble-free test drive of approximately 40 km, I drove a longer distance yesterday, and after another roughly 50 km, the problem reappeared (including the same error code in the diagnostic memory), so it happened again after almost 100 km.

Does anyone have any other good ideas?

Rainer K. wrote:

I think the 00519 is a consequence error of the 00575

.

Yesterday I did some test drives (short distances), read the error codes, deleted them if necessary, and continued. I noticed that error code 00519 often appears on its own, while error code 00575 sometimes appears in addition to it.

It seems the opposite is true; 00575 appears to be a consequence of error 00519 – that's strange!

Since I cut the tip of my finger while grating carrots last weekend, I haven't been able to do much with the car lately, but I already have diesel filters, air filters, and a large syringe (for checking the wastegate) on hand... However, I suspect that changing the filters won't make much difference.

Ugh... Rainer, the actual boost pressure of 2083 millibars is the current reading... it should be around 1950 millibars, which is probably the correct value.

The problem still persists . So far, the N75 and the three surrounding hoses have been replaced, and the air filter and diesel filter have been renewed.

The catalytic converter was gently "tapped" from below and doesn't seem to have any loose internal components. I'm going to hold off on disassembling it for now, as new seals and a connector piece would likely be needed for reassembly, which aren't cheap. I'm also ruling out the catalytic converter for now, since a clogged one would probably lead to insufficient boost pressure, right?

Unfortunately, I only realized at the end of another test drive today that the injection timing is still trending towards being too late, further than what I had noted in my records. At 90 degrees, the start point is close to the lower limit, but within tolerance. However, after the test drive, the engine was very hot, and the start point was sometimes below the lower line – meaning it was actually too late. I will probably need to adjust the pump to an earlier timing anyway.

The timing belt was replaced a few months ago, but the problem didn't appear immediately after that. I plan to do another test drive tomorrow and log the air-fuel ratio and injection timings at full load and during the problematic time. But initially: Could this all be related? Shouldn't the error message be different if that were the case? Can a delayed start of injection cause excessive boost pressure?

The boost pressure of 2083 mbar is definitely not normal for the 1Z engine, right?

Edit: Addendum: I forgot to mention: The wastegate rod is common; I can easily press it with a large syringe.

Thank you!