AAT Error? Milk Replacer Feeding Questions.

Hello!

Could one of the AAT technicians please check the connector for the engine speed sensor? According to the wiring diagram, one pin on the sensor supply line should be at a stabilized 5V, but in my case, two pins are grounded and one goes to the control unit.

Here's the translation:

'Background: As I described in this forum before, my R100 has quite a frustrating driving behavior. It exhibits occasional misfires at idle, load surge issues (which vary – sometimes they disappear when the engine is in the warm-up phase, but reappear when the engine is fully warmed up), jerking during cruising at speeds around 1500 RPM or lower, and generally a rough running engine. Fuel consumption is stuck at 7-8 liters; I can't get it any lower! I should also mention that the engine management system's jerk dampening function is working because when I disconnect the speed sensor connector, the bike becomes almost undriveable (due to excessive load surge).'
The initial diagnosis from an Audi workshop was: the ESP (Electronic Stability Program) unit was worn out (the pistons in the fuel injection control system were sticking). The ESP has now been replaced, but there is no improvement.
Based on a suspicion, I replaced the sensor for the engine speed, which resulted in a slight improvement!

Here's a list of everything that is new or definitely in working order:

ESP.
NHG.
LMM and all other donors are okay!

My theory:

Since the system receives a speed signal, the vibration damping and low-speed control are active, but they cannot function correctly because the signal is at a different voltage level (because the inductive sensor has a permanent magnet, it also generates its own current, which explains why the system doesn't detect an error).
I believe the issue with the thrust cutoff not working correctly is due to the signal level being too low at lower engine speeds for proper detection by the system.

Perhaps one of you can help me with this: Should the donor be provided for, or not?

Best regards,
Andi.

Andi aus dem Ösiland wrote:

According to the circuit diagram, one pin on the sensor power line should be floating (stabilized 5V). However, in my case, two pins are connected to ground, and one goes to the control unit! My theory: Since the system receives a speed signal, the vibration damping and low-speed control are active, but they cannot function correctly because the signal is at a different voltage level (because the inductive sensor has a permanent magnet, it also generates its own current, which explains why the system doesn't detect an error). Perhaps one of you can help me with this: Yes, the donor must be provided for, or not?

What kind of circuit diagram do you have?

The speed sensors of all the engines I'm familiar with do not receive a 5-volt signal.
Its three conductors consist of the two winding terminals and one shielding wire. Two of these are connected to ground in the direction of the motor.

Quote:

I would attribute the issue with the thrust cutoff not working correctly to the fact that, for that system, the signal level is too low at lower engine speeds for proper detection.

You could try this test: disconnect the sensor connector while the engine is idling.
I bet the engine will stop immediately.

If the signal from the sensor is too weak for evaluation, should it then not be able to run in idle mode or start at all?

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

'Hi,'

I'm sorry that I can't help you with your very specific question.

But:
Are you absolutely sure that the valve timing is perfect?
I've gained quite a bit of experience with my AAT over time. Just last week, for example, I had to replace the head gasket (ZKD), and at the same time, I also replaced the water pump (WaPu), belts, and timing belt (Zahnriemen).
After that, the car started roughly when it was cold. So far, so good, I had experienced this before after the last timing belt change; the air-advance system seems to require very precise adjustment.
However, I actually had all the symptoms that you described above!
It exhibited jerky hesitations (mostly when cold), similar to a faulty negative feedback generator, and frequently responded late, poorly, or not precisely as desired to driver inputs. Overall, it displayed unreliable behavior in responding to the driver's commands.
After that, the timing belt was adjusted with extreme precision. Since then, it's been running incredibly smoothly, better than ever before. It starts up as soon as I think about turning the key, it always responds to the accelerator pedal, and there's no more jerking. It's even better than after the last timing belt adjustment.
I even noticed a 'gradual deterioration' of over 80,000 km with the last timing belt. At the end, it started slightly worse and slowly began to exhibit throttle response problems again. Can this happen if, for example, the tensioner and also the belt age ?

EDIT:
I also always experienced that jerking when decelerating from 1,500 RPM. I suspected it might be related to the clutch. I'll check if that issue is gone now.
Also, last week, before the final adjustments, I also experienced a rougher engine running sound. Now it's back to how it was before, which is pretty good.

First of all, THANK YOU for the answers!

@ Ulf

I got the wiring diagram from another forum, but I'm sure it's the correct one! I also already performed the 'check at idle' test, and the result is that the engine runs with a slightly higher RPM after a brief hesitation, of course with reduced power, but not 'rough,' which also proves that the idle speed control isn't working correctly.
'In my wiring diagram, the sensor is connected to the sender supply line. What's also confusing me is that, according to the schematic, the sensor's shielding is connected to a center tap of the sender's coil, which isn't the case for me; it's only connected to the connector pin! Regarding the ECU: My ECU doesn't even reduce the injection amount when I disconnect the solenoid valve for ignition timing adjustment, and there are no error messages either!'


@ Markus H.

'Approximately 5,000 km ago, the timing of the ZKD (cylinder head gasket) was readjusted by an Audi mechanic. With the new ESP (installed about 2 months ago), the pump, which is the same type, was readjusted again by the same mechanic, but unfortunately with the same result (perhaps a little better!). How did you properly adjust your AAT? Did you also set it slightly early, even statically? According to the 'Audi PLAN' procedure, the engine starts a bit worse in colder temperatures, so I told the Audi mechanic to adjust it more towards being slightly advanced. Now it always starts immediately! Did your AAT also experience occasional severe vibrations under full load at 1900-2100 RPM with the incorrect setting?'


Well, I'm now grateful for any advice; I've lost interest in the car for quite some time.

edit: Oh yeah, my EGR has been deactivated since I got the car because I had noticeable power drops during acceleration (First, I disconnected the solenoid valve for the EGR >> The problem disappeared. Now it's also sealed with a metal plate). Could the EGR have such a significant influence on the lambda value when using an AAT?

Does anyone here drive an AAT (presumably a type of vehicle) with a fixed EGR valve? And does it run normally?

Greetings,
Andi.

Andi aus dem Ösiland wrote:

In my circuit diagram, the sensor is connected directly to the power supply line for the actuator.

Actually 5 volts? Voltage values for power supplies are not actually indicated anywhere on the original VAG schematics that I am familiar with... However, I am not familiar with the AAT schematic.

Or do you mean the donor mass?
It is kept separate from other mass connections for that reason.

S..., that's the donor mass .
In my PDF, next to the 'D101', there's a character that looks like a '+'. The second line in the '-' is probably a small speck of dust that was picked up during the scanning process.

I didn't find the 5 volts in the circuit diagram; I simply measured the voltage between the two pins of the temperature sensor and found that they were connected to 5V.

Well, my knowledge is slowly fading away. It can probably only be due to either incorrectly set valve timing or the engine control unit (ECU) itself, although I'm leaning more towards the latter!

Here's another strange observation: When I drive in heavy rain, all the symptoms are better, or even almost disappear temporarily! The rain should only affect the mass airflow sensor (MAF) and the temperature sensor for the intake air. In the repair manual for my engine, it also states that a faulty intake air temperature sensor can cause jerking during coasting (literally: jerking during cold deceleration). However, I find it hard to believe that the intake air temperature sensor could have such significant effects as I'm experiencing!

I've heard of models with faulty anti-vibration systems, but I haven't had one to test myself! (My Bosch service technician master had one like that.)

Hello again!

After my problems still haven't been resolved, and I haven't decided to buy a VAG-COM yet (it's just too expensive), I measured the voltage at the fuel injection start adjustment valve in the intake manifold: it was 12.9V, meaning it's being fully activated. Apparently, my AAT (air temperature sensor) would like to delay the injection slightly, but the electronic boost control (ESC) unfortunately doesn't allow this (which would explain my relatively noisy engine sound).

I know that I'm currently trying to solve my problem with rather primitive methods, but I've already invested about €1500 in workshops in my area...

Has anyone ever measured the voltage at low RPM with a warm engine using their AAT (Air-to-Air Temperature) sensor?

Greetings,
Andi.

The technical articles explain quite well how to adjust the start of injection using a voltmeter. -> check it out!

Hello wolfi_b!

Haha...

I know the article inside and out, but I just didn't have it.


Unfortunately, it's not yet possible to perform the tests during the journey.
'Apparently, the older AAT systems are a bit more sensitive than the 1.9 versions when it comes to the start of injection.'
3. It's possible that another AAT driver has already measured this and it would only take a few keystrokes for them to let me know.

I just wanted to know if there should still be some leeway towards a later timing when checking the AAT (Angle Advance Timing) at idle with a warm engine. Knowing the voltage reading of another AAT could help me determine that.

I'm starting to really need VCDS (VAG-COM) like I need a slice of bread.

Greetings.
Andi.

Hi,
"On my AAT, the fuel injection adjustment is also hitting the stop in the low-load range. I had previously adjusted it to a point where the voltage/multimeter needle was barely fluctuating at idle, but after that, it didn't start as well."
I don't know if this is supposed to be like that or if it's due to aging.

Good morning!

I have now solved the problem by 50% after carefully studying the AAT/AEL Representative Guide.

The cause of the rough engine running, high fuel consumption, and surging during cruising was a faulty brake pedal monitoring switch. The switch had a resistance between 100 and 200 ohms when the brake pedal was not pressed, which forced the control unit (ECU) to repeatedly decide whether or not to adjust the engine parameters, sometimes multiple times per second, thus explaining the rough running. I also have an explanation for why the warning light didn't illuminate: The error 'brake pedal monitoring - implausible signal' is only stored after a certain period of complete malfunction of both switches on the brake pedal (pedal monitoring switch + brake light switch). I tested this myself!

After replacing this switch, I'm getting over 1000 km on a full tank, and the car pulls much better from low RPM. Also, when coasting, you can barely hear the engine anymore... }

Oh yeah, that vibration from 1900 to 2100 RPM has completely disappeared too!

Now, only my occasional misfires remain, but they now appear in a different form, namely as 'softer' misfires (only in low gear and at low RPMs). The load change noises are also softer, but still present.
I'm going to have the fuel injection timing checked again because this error could potentially have affected the fuel injection start setting. The fluctuating fuel quantity might have prevented it from determining the correct injection start point.

Does anyone know if it's possible to open the old-style throttle valve air mass sensor, and if so, how?

I'll let you know if there's any new information!

Greetings.
Andi.

Hello everyone!

I'm still trying to fix my misfire problem. My question about whether the old mass airflow sensor (MAF) could be opened is now irrelevant; I simply opened it up and immediately noticed significant wear in the area where the throttle valve plate operates most frequently under partial load. I temporarily shifted the plate that holds the resistance element a half-millimeter towards the axis of the potentiometer, effectively creating a 'new' MAF sensor (I've also read about bending the slider, but I don't think that's a good idea). Well, it didn't really help, except that it seems to be drawing air slightly better! Oh yes, you obviously need to seal the housing with sealant because it's not normally designed to be opened.

Now, the actual question: Could my misfires be caused by worn-out injectors? I've read about many small symptoms in this forum, but no one has reported experiencing misfires directly. The four standard injectors have approximately 176,000 km (about 109,000 miles) on them, while the one with the NHG (new high-pressure injector) has only about 15,000 km (about 9,300 miles). It was replaced because of suspicion, but it didn't make a difference. I suspect that the relatively new NHG is maintaining its defined opening pressure, while the others are more or less worn out, and therefore their injection timing is no longer correct. So far, I've only heard about injectors with too low an opening pressure (meaning the spring weakens and the injection starts earlier...).

Perhaps one of you has experienced issues with faulty injectors and can share some information with me! (The exhaust from mine smells like a vintage diesel engine.)

Best regards,
Andi.

Hello everyone!

I just wanted to quickly update the post because, thanks to Markus H., all the problems are gone now. The car pulls even better at low speeds and is also a little quieter than before (unfortunately, I never had a 'reference' AAT).

'I just adjusted the fuel injection pump again, rotating it about 1mm earlier while the engine was running. Now, according to VAG-COM, it's completely outside the tolerance range, but my AAT (air temperature sensor?) seems to like it that way! I'm wondering what the control system is doing that makes the engine run quieter when I rotate the pump earlier (towards the engine)? This phenomenon doesn't really make sense (usually, it would be louder knocking), but apparently, the control characteristics are now working correctly again. I suspect this might be related to my injectors, which have almost 200,000 km on them.'

So, topic successfully concluded: No more glitches, performance is there, load changes are smooth as silk, and silence inside!

Beste Grüße u. DThank you!
Andi.