Failed AU Exam: Reasons and Solutions

I went through the customs check on Wednesday... and it wasn't a quick process at all.
The CO level is between 1.5 and 2, instead of the required 0.3.

I've been experiencing a rough-running engine for some time now, especially when idling.

The day before, we had installed a metal catalytic converter, but the mechanic said that it definitely wasn't due to the catalytic converter.

First, the mechanic said that the mixture was far too rich and that the engine was misfiring.
So, I started by installing new spark plugs and reducing the fuel pressure from 5 bar to 4 bar (which is the standard setting).
After that, he still had it... you can hear it very clearly, he said.
I then remembered that during the last measurement, I had a spark timing of 32° before top dead center (TDC), even though it should have been 12°.

Okay, so I looked up some information on "MWBs" at home.
Lambda control checked, knock control, injection system, etc.
Check the intake system for leaks, inspect the fuel injectors, and generally perform whatever checks are possible.

The only irregularity I've noticed is the high learning rates for mixture formation. They are at -16.4% (additive, target: -10% to 0%) and 3.8% (multiplicative, target: -8% to +8%).

The unusual driving behavior occurs both during the cold start and warm-up phases.
Since the oxygen sensor is providing correct readings, everything seems to be okay.
The ignition timing tolerance appears to be within acceptable limits.
The LMM is providing values around 4 g/s (target: 2.5...4 g/s), so it's also working correctly.

It correctly responds to changes in airflow (i.e., additional air entering through a detached hose) by indicating a value for an overly lean fuel mixture.

The question now is, why are the learning rates so high?
What factors can cause a high CO (carbon monoxide) reading?

Engine:
1.8L naturally aspirated engine (ADR compliant) in the Audi A4 (1997) with Bosch Motronic system.

Since this forum is called 'Diesel Mechanics,' I'm not sure if my response is even wanted here, but anyway...

Checking the MAF sensor at idle is almost useless. You should try logging the MAF sensor values at full power, preferably while accelerating from 2000 RPM to the redline in 3rd gear (or a higher gear).

-Uwe-

Hi Uwe.

The values for the mass airflow rate (MAF) go up to almost 87 g/s... I've heard from some people that this is too low, but they also have a different intake system (with a switchable intake manifold).

I have just successfully reset the learning parameters.
I believe the last time I performed a reset was when I adjusted the fuel pressure.

The engine is warming up now; let's see if these misfires are still audible.

Hello,


Please check your throttle valve potentiometer (between terminals 4 and 7, approximately 1000 ohms).
With the connection between terminals 5 and 7 closed, the resistance is 1500-1600 Ohms.
With the switch open, the resistance is between 5 and 7, with a value of 700-900 Ohms.


Check the coolant temperature sensor as well.

If you need any further information, please let me know.


Greetings.

Mati.

I already checked the throttle potentiometer, as well as the coolant temperature sensor (G62).

Uwe@Ross-Tech wrote:

Since this forum is called "Diesel Mechanics," I'm not sure if my answer is even wanted here, but anyway... Checking the mass airflow sensor (MAF) at idle is almost useless. You should try logging the MAF values at full power, preferably while accelerating from 2000 RPM to the redline in 3rd gear (or a higher gear). -Uwe-

But of course .

Currently, this is being tested.
http://schraub-selbst.de

What coolant temperature is displayed in the VAG-COM measurement block for a motor that is at operating temperature?

Best regards, Rainer.

Standing speed: between 78 and 87 [units]. Speed while moving: around 90 [units].

After I was able to delete all the learned values by resetting them, everything was fine until the engine reached its operating temperature of 85°C... The learning value for mixture formation at idle first showed -3.6%, then -5.5%... and it's still there now.

After reaching 85°, it started sputtering again from the exhaust, and the engine ran a bit rougher. I then proceeded to complete the remaining basic adjustments.

I just got back from the test drive, and the learning value for mixture control at idle is still acceptable (a negative value), but the value for partial load is still showing as 0%.

I'm still surprised by the high fuel consumption. I used to get 6-8 liters per 100 kilometers, but now I'm consistently getting over 10 liters per 100 kilometers.

Anyone have any more ideas?

The values of the LMM can reach up to almost 87 g/s.

How many horsepower should the engine have? 125?

At what altitude above sea level did you take this measurement?

What is the year of manufacture of the car?

At sea level, the maximum value of the mass airflow rate (MAF) in g/s should be approximately 80% of the engine's power output (PS). This rule only applies to gasoline engines! So, for an engine with 125 PS, you should see a MAF reading of around 100 g/s. However, if this measurement is taken at a higher altitude, it's necessary to compensate for the reduced air pressure, especially in naturally aspirated engines.

-Uwe-

"It comes with 125 horsepower as standard, but mine has a bit more... around 170 horsepower."

The altitude above sea level is approximately 100 meters. At the time of measurement, the temperature was around 6°C and the atmospheric pressure was about 1000 hPa.

Year of construction: 1997.

"If you say he needs more air for increased power, why can't I get above 85 g/s? That would be too little even for a stock engine."
Even after removing the air filter, it still doesn't get any better.

Please check the vacuum system for any signs of damage caused by martens or other animals.
We also once observed the effect that the adaptation values repeatedly...
wegliefen. That's what it was.

Best regards,
Rudi

As standard, it has 125 horsepower, but mine has a bit more... about 170 horsepower.


Great.

Can't you just reveal the type of tuning and the modifications made right away?

We are assuming a standard 1.8 engine here!

I assume that the changes I made will not affect the air-fuel mixture, as nothing was modified in the engine control unit.

Manifold cat converter - metal catalytic converter - 2.5" outlet after the catalytic converter.
Carbon air filter box.
Fuel pressure increased from 4 to 5 bar (reverted to original setting before emissions test).
Flywheel simplifies [the process/task].
Compression reduces (thinner head gasket).
etc.
The performance test in April showed 176 horsepower.


But again, regarding the airflow... I already noticed in March during the measurement that it only has 87 g/s... and other 1.8 models have more... why does mine have so little?
Perhaps it's still the lambda sensor (oxygen sensor), even though the target value is reached at idle?

This morning, I created two log files while the machine was running at a speed of 2000 to 6500 RPM in its third gear.
Also, in addition to ad group 00, there's also an issue with the lambda control at idle.

http://home.arcor.de/turboschubser/log/

Notably, the airflow is only 82 g/s!!!

Note: The intake air temperature is only this high because the intake hose connecting to the air filter box is missing (it broke). The outside temperature was approximately 10°C.
However, I also achieved the low fuel consumption of 6 liters per 100 kilometers even with the hose missing.

The fuel consumption has only been this high since the conversion to a metal catalytic converter (200 cells) and the change of the gearbox (to a V6 gearbox; which is 3% longer) .