Rough idle, error codes G80 and G28

Hello,

My Audi A6 C4 (manufactured in 1997, engine code AEL) has recently started exhibiting a rough idle.

Above approximately 1000 RPM, it suddenly returns to normal. I only noticed it after a longer highway drive; up until then, it was running completely normally with no loss of power and no warning lights.

Error diagnosis: see attachment.
The errors reappear after deleting.

I have checked the continuity of the wires from connectors G80 and G28 up to the control unit -> OK.

The following sensor readings were taken with the engine cold:

The needle sensor G80 has a resistance of 100 ohms between its two contacts.

The crankshaft position sensor (G28) has a resistance of 1 kΩ between the front and middle terminals (facing towards the front of the vehicle).
Further measurements between the other pins showed "no connection."
Can anything else be measured here?

Edit 17:53Uhr: Habe gerade den G28 mal rausgeschraubt. Dieser weist Schleifspuren auf. Hat der sich ausgedehnt? Ist das schlimm oder bekanntes Phänomen ohne Probleme zu machen? See attachment.

I would appreciate any advice on what else I can check or where I might still be able to find the error.
Thank you very much!

Hi there,
The resistance values are initially fine; the third connection on the speed sensor is ground/shield.
Nevertheless, I would carefully check for damage to cables and connectors due to the frequent, intermittent errors.
Das schlechte Leerlaufverhalten kann damit zusammenhängen, muß aber nicht. Schau Dir die Korrekturwerte der Einspritzdüsen, den Einspritzzeitpunkt, und alles was die Einspritzpumpe sonst noch liefert an. SpDoes that have any value?
The scratches on the G28 suggest that the distance is too small. If a sensor wheel is installed, is it loose?
hg
Herbert.

Hi,

Are the crankshaft bearing bolts tightened?

Best regards, Rainer.

Thank you for your answers.
I was able to search a bit further today.

I removed the G28 and tried to feel around for the crankshaft gear with a screwdriver. I tried pushing it in every possible direction, but nothing moved.

I haven't checked the screws on the crankshaft bearing yet (I believe you would need to remove the oil pan to do so?). I'd like to avoid doing that for now.


I tried to press the G28 slightly to reduce the distance, but in doing so, the metal casing cracked and some oil leaked out. It probably sucked in the oil somehow.
I replaced it as a precaution.
Unfortunately, there is no change in the situation.

The errors are still the same sporadic errors and they reappear after some time (not immediately).


Then I checked the dynamic fuel injection timing.
Graphs are in the appendix.
(The image says "Coolant temperature not high enough," but that was fine shortly after.)

-> The message that appeared when the engine temperature was correct was essentially: "Injection timing too early for display."

I temporarily installed the rear timing belt with very little tension, and the injection timing improved.
For me, this suggests a stretched timing belt. Am I interpreting that correctly?

Overall, this seems strange to me.
VCDS says the injection timing is too early.
Logic tells me that belt stretch causes a delay in the injection timing.
It doesn't quite fit together.


I've attached 3 more photos below.
1. Camshaft sprocket with matching marking.
2. + 3. Crack/split in the flange of the fuel injection pump extending to the engine block.
The notch on the impeller of the ESP (electric submersible pump) is offset to the left by approximately half a tooth compared to the notch on the housing.
It also suggests a late injection timing.

Am I making a mistake in my thinking?

If only the injection timing adjustment on the pump remains, I would proactively replace the belt, as it doesn't look very new anymore.

What else can I check?
"Thank you!"

Greetings.
Benny.

Hello,

Does the injection start control work, or have you only been looking at it in the basic setting mode so far?

Best regards, Rainer.

Hello,
I once logged the fuel injection data while the car was stationary (at various throttle positions and engine speeds).
See attachment.
It doesn't look right to me when I compare the actual values to the target values, does it? But where is this discrepancy coming from?

Dieselfilter habe ich inzwischen getauscht, um Luft/Wasser auszuschließen. No change.

I measured the resistance of the N108 injection timing valve: 15.6 ohms.
The actuator diagnosis also affects this (it briefly comes out of its erratic behavior, with a slightly higher RPM than idle, and then returns to the jerking motion when the RPM drops back to idle level).

I then unplugged the connector for the N108 and immediately the noise stopped.
Voltage measured at the connector of the MSG: approximately 14V.
(However, in the default view, the yellow dot was not visible within the window.)
It also accelerated surprisingly well and reached a high speed.
Once he plugged it back in, the hammering started again.

I have to admit, I still don't fully understand the connections.
Do these details help you?
What should I test next?
Thank you.

Hi there,
I would first mechanically adjust the valve timing of the camshaft and the injection pump correctly - with a toothed belt tensioned according to specifications. Furthermore, you tried to change the ESP timing by adjusting the belt tension. It also appears that the belt in the picture has transverse cracks, so it needs to be replaced.
hg
Herbert.

Hello Herbert,
Thank you for your feedback.
I only adjusted the belt tension temporarily to see how it would affect the timing.
Yes, it seems like it's worn out; I had already suspected that, as I mentioned above.
A new one has been ordered.

Hopefully, I'll be able to change this next week (and properly tension it).
Then I will check the start of the boost using a measuring instrument and, if necessary, correct it.
The sealing gasket for the drain plug on the ESP should always be replaced. Can anyone tell me the dimensions of the gasket? Is it a copper ring?

Regarding the general condition of the engine:
It hasn't started up as well since I bought it 4 years ago.
I was surprised by how quickly and smoothly it started, and also how well it responded to the accelerator pedal when the N108 was disconnected.
Does it then operate based on predefined values, rather than being adjusted via the N108 input?

Hi there,

Quote:

The gasket for the drain plug on the ESP should always be replaced. Can anyone tell me the dimensions of the gasket? Is it a copper ring?

If your ESP unit requires a sealing ring, you can find the correct one at Volkswagen/Audi dealerships.
And as I said, start with the camshaft, not somewhere in the middle of the process.
hg
Herbert.

When starting to work on the camshaft, does it involve removing the valve cover and checking the position with a camshaft alignment tool?
Visual inspection:
The notch on the rear camshaft sprocket is precisely aligned with Top Dead Center (TDC) (the markings on the front of the sprocket also match; the TDC marking on the flywheel window also aligns).
Should I still replace the valve cover gasket and do a complete inspection?

Hello,
The AEL engine has two timing belts. There likely isn't a factory-installed TDC (Top Dead Center) mark on the camshaft near the pulley side. The camshaft is adjusted using a ruler on the transmission side, and the timing belt is tensioned by loosening the camshaft sprocket on the pulley side.

The fuel injection pump is adjusted using a marking, and then it's secured by blocking it with the small metal plate that needs to be removed.
The timing belt is also tensioned on the drive side with a loose camshaft pulley, so there shouldn't be any original markings on the pulley.

@Herbert
For the 5-cylinder direct injection engine, it is correct that the fuel injection pump is adjusted using the timing belt. An eccentric idler pulley and a matching tensioner are used for this purpose.
Finding the perfect settings for a worn-out engine is a game of patience.

Hello klahaui,
Someone has marked a tooth on the timing chain wheel and the housing with white marker, and these markings align with the mark on the flywheel. (It's not very precise, I realize that.)
I've just checked again very carefully, and it seems there might actually be a slight misalignment between the notch on the rear camshaft wheel and its corresponding mark.
You can see the notches in a photo that was posted earlier in this thread.

According to the "How To" book, my ESP will be adjusted by setting the drive wheel (the rear camshaft sprocket) and measuring its position with a dial indicator (using adapter 2066).
I can't see the "metal" you're referring to on my ESP guitar.

Die Spannung des hinteren Riemens erfolgt bei meinem Auto statisch durch ein exzentrisch gelagertes Rad (ohne Feder). See photo.

Greetings.

Hi there,

Quote:

For the 5-cylinder VEP engine, it is correct that the fuel injection pump is adjusted using the timing belt. An eccentric idler pulley and a matching tensioner are used for this purpose. Finding the perfect settings for a worn-out engine is a game of patience here.

Ganz bescheiden angemerkt, was ich hier in sowas ähnlichem wie einem RLF lese. In brief.
- Mount the ESP (Electronic Stability Program) module centrally within the elongated holes.
- The markings on the ESP wheel and console are misaligned.
- Mount and tension the ZR (Zero-Ridge) cable.
- Static adjustment (using a dial gauge) with the drive gear released by the Northwest company (ZK at the rear); engine must be at Top Dead Center (TDC).
- Dynamic adjustment using a diagnostic tool, by rotating the ESP within the elongated slots.
I might be wrong about that.
hg
Herbert.

Hello Herbert,
Excellent description. I hadn't realized there were elongated holes in that area. That significantly simplifies the fine-tuning process (especially the dynamic adjustment).
I'll look into it next week. (Hopefully I can find the bug there.)
Thank you.

Hello,
Since I believed the AEL (presumably a component or system) had the same structure as the ACV in the T4, I have to agree with what Herbert wrote.

Sure, here is the translation of the text from German to English:

"VG Thilo" translates to "Best regards, Thilo".

Here's the translation:

Slightly off-topic - is there a discernible reason why they used this particular timing belt layout and adjustment in the ACV engine?
hg
Herbert.