AFN Idle Vibration: Causes & Solutions

Hi there,

I have an aftermarket fuel injection system in my VW T3 bus, which has been working perfectly for about 60,000 km. Lately, I've felt that it's using too much fuel (although I might be wrong). In any case, it's not reaching its full power; the maximum speed is 135 km/h instead of 145 km/h. The air filter is new. Also, it has extreme vibrations at idle.
"This weekend, I ran the diagnostics: no errors in the memory, no unusual values in any of the measurement blocks. The maximum boost pressure is being achieved without any issues. The maximum deviation in the idle speed control is +0.6 to -0.4."
"Especially the vibrations are so strong that they really scare me. At a higher RPM, it sounds normal again."
I'm at my wit's end, and I haven't found anything suitable with my searches either.

I hope you have an idea.

greetings
Volkswagen T3 Syncro AFN.

dieter wrote:

Especially the vibrations are so strong that they really scare me. At a higher RPM, it sounds normal again.

Hello Dieter,

"I've experienced this before with my 1Z. I gave it a little gas, and the vibrations disappeared. However, I only heard it; I didn't feel anything."
"In my case, it was simply the serpentine belt that was oscillating at idle. You should have seen what the tensioner pulley was doing. However, it was almost impossible to do anything about it. Since the vibrations were caused by the (not perfectly centered) vibration damper, and you can't change anything about the tensioner pulley, I just had to live with it. After the weather got a little warmer and the new serpentine belt had broken in a bit, it went away on its own."

Maybe it's something similarly simple with you.

Best regards,
Markus.

hello markus,

I've seen that about the tensioner pulley before, and the serpentine belt is new. It would be great if that was all it was.
"However, the Lima pulley with a freewheel, which comes standard on many Lima models, probably helps. I replaced it last year with a fixed pulley because it was defective (the alternator was no longer being driven). Before that, the belt ran very smoothly."
I will probably reinstall the free-running clutch soon.

Hello,

I've had an issue with my AFN (which, coincidentally, is in a VW T3 ) for over...
20Tkm, JX Lima with JX shock absorbers, and no other modifications.
Having problems with it.
Can you rule out a defect in the flywheel?

Regards,

Maciek.

Quote:

Can you rule out a defect in the flywheel?

No, I can't. This is already the second ZMS (presumably a type of motor or component), and it's about 20,000 km old. The first one apparently didn't have any grease, the springs broke, and completely destroyed the flywheel.

Please correct me if I am wrong:
If the fuel injectors are clogged, shouldn't you be able to see it in the closed-loop system through extreme correction values?

Hello.

After replacing my fuel pump and injectors, my 1Z engine runs smoothly like a sewing machine when idling.
With a new pump and the old injectors, the engine block still moved approximately 1 cm, with a barely noticeable adjustment in fuel quantity.
In addition, the third nozzle made a different "sound" when opened compared to all the others.
While removing the old injectors, I noticed that the injector from the first cylinder was completely wet, which is a sign of fuel dripping.

The injectors only had 40,000 kilometers on them, and I'm astonished at how worn out they were after such a short distance.
The "sound" of the new ones is the same across all cylinders (like putting a screwdriver to your temple).
It sounds like a small hammer hitting a large anvil.

Even the ancient Germanic tribes used a long screwdriver to "listen" to their diesel engines, lol.

Best regards.
Maik B.

Deleted upon request.

Hello,

I read this with interest, as my Audi A4 81kW AFN also has these vibrations at idle.

The workshop I went to mentioned something about re-coding the pump/control unit after consulting with Audi.
Personally, I only see the result as an increased idle speed and the car no longer accelerates as smoothly as it did before.

Therefore, my question is whether anyone here is familiar with this problem and has a solution ready.
Currently, the car is drivable, but I have some concerns about the fuel consumption and the lifespan of the parts, especially since everything seems to be out of alignment.

Regards,
Sven.

dieter wrote:

Please correct me if I am wrong: If the injectors are clogged, shouldn't you be able to see it through the closed-loop control system by observing extreme correction values?

Hi.

We are currently operating under that assumption, but it hasn't been "proven" here yet (in the sense of removing, inspecting, and actually finding that the nozzle is clogged and has very low flow).

Hanging nozzles should, AFAIK, be more noticeable due to forceful hammering rather than vibrations .

What is the operating speed range where the engine vibrates? If you give it a little gas while it's idling, at what speed does it return to normal operation?

A ZMS (Zentrale Motor Management System) can likely build up over time - especially if the resonant frequency of the engine mount (which is not a "normal" engine-vehicle combination) coincides with that of the ZMS .

Hi there,

Okay, here's the continuation finally.

The vibrations were coming from a faulty exhaust muffler!
The right-hand bracket (which is located in the T3 bus) was corroded, and the exhaust pipe was only loosely attached to the bracket.

After changing the container, I now experience strong resonances at around 3000 RPM. However, I'm familiar with this effect, and it can be resolved through experimentation. I suppose one has to live with such issues; it's essentially a prototype.
Given that the entire engine seems to be extremely sensitive to such changes, I believe it's possible that similar effects might also occur in production vehicles. By the way, I also have a flexible pipe between the turbocharger and the catalytic converter.

greetings
dieter

Hi,

Since the entire engine apparently reacts extremely sensitively to such changes, I believe it is possible that similar effects also occur in production vehicles.
The unfortunate thing is that even the standard TDI models (at least in the past) were plagued by such resonance problems.
I had to experiment for a long time with my Golf 1Z until the resonances disappeared.
In a company fleet I know of, which included several Golf and Passat diesel vehicles, almost all of them had the same issue, but no one bothered to address it.


By the way, I also have a flexible pipe between the turbo and the catalytic converter.

'This part broke on my Golf at 20,000 km. As a result, the vibrations became even worse. The new one lasted until I sold the car at 150,000 km.'

Hi there,

I'm still experiencing the resonance problem, and surprisingly, I can't seem to get it under control. So, my question to the experts is: is it possible that the resonances are being caused by a different exhaust pipe?
Just to reiterate, I only replaced the muffler (with the tailpipe). It's the same type of muffler. There were no such problems before. The current tailpipe has a slightly smaller diameter.
I would simply try it out if I could remove the exhaust pipe without the flexible section.

greetings
dieter

T3 Syncro 16" AFN

Hello,

Is your exhaust system not installed in a way that allows for thermal expansion and contraction?

Best regards, Rainer.

Quote:

Is your exhaust system not mounted in a way that prevents stress?

Yes, as far as I can remember, it already does.
I've had something like this happen before. I loosened the flange between the exhaust manifold and the turbocharger pipe, allowed everything to shift slightly, and then tightened it back up, and it was okay. But that's not working now.

Hello!
While searching for a solution to the annoying rattling noises I'm experiencing at idle in my 1996 Golf3 AFN, I came across this thread.


'I've experienced something similar with my 1Z. I gave it a little bit of gas, and the vibrations disappeared. However, I only heard it; I didn't feel anything.'
'In my case, it was simply the serpentine belt that was vibrating at idle. You should have seen what the tensioner pulley was doing. However, it was almost impossible to do anything about it. Since the vibrations were caused by the (not perfectly centered) vibration damper, and you can't change anything about the tensioner pulley, I just had to live with it. After the weather got a little warmer and the new serpentine belt had broken in a bit, it went away on its own.'


My tensioner pulley is wobbling quite a bit, and the noises seem to correspond to the movements. Could the spring in the tensioner pulley be worn out?


'However, the Lima pulley with a freewheel, which comes standard on the larger Lima models, probably helps with this.'


How can I tell if I already have one of those pulleys?


I've had an issue with my AFN (which, coincidentally, is in a VW T3 ) for over...
20Tkm, JX Lima with JX shock absorbers, and no other modifications.
Having problems with it.


What kind of vibration damper are we talking about here?

My TDI has an automatic transmission. When I'm in 'D' and holding the brake, the vibrations are stronger than when I'm in neutral ('N'). However, turning off the air conditioning doesn't really make a difference.

Relatively clueless,

Jörg.

Hi there,

Okay, I'll show some mercy then:

Here's the translation:

"A free-running clutch can be identified by the fact that the pulley on the front of the alternator has a cover on it. If you remove this cover, you'll see an internal spline. If the cover is missing (as it was in my case), you can assume that the free-running clutch is defective."
"In my case, the freewheel was so defective that it no longer drove the alternator. I've now replaced it with a fixed pulley, but I'll probably switch back to the original design, despite the cost (around 90 EUR)."
The loudest part in the LL (likely referring to the engine compartment) of my engine is the tensioner pulley.

2. Vibration dampers, which are the pulleys on the crankshaft. Nowadays, these are not just pieces of metal.

The "correct" vibrations, which also occurred at higher speeds and caused the entire body to vibrate, were clearly coming from the exhaust system in my case.
It's working fine for me now. I still can't detect any system there, though.
Everything was relaxed and normal. After about 1000 km, it improved and is now practically unnoticeable.

greetings
dieter