Air bubbles in the supply line to the Audi 80 B4 fuel pump (1Z)

Hi everyone.
While searching for the cause of my 'jerking' after the fuel pump replacement, Tino Kossmann (thank you again) noticed small air bubbles traveling from the diesel filter, through the supply line, and into the pump, approximately once per second. This wasn't happening on his B4 TDI, and it doesn't seem normal. Could these bubbles, if they enter the high-pressure section of the pump (if that's even possible), be responsible for the jerking during the transition from idle to the lower load range? This could happen if the pump or the injection start valve tries to adjust, but doesn't have a consistently high pressure.
Furthermore, the question arises as to where the air could be coming from.
The car definitely doesn't lose anything by switching from diesel. So, probably just the hose connections in the area of the filter or the (screwed-on?) filter cover?
Normally, there should be an error entry in the engine control unit (ECU) if air in the pump prevents the desired fuel injection timing from being achieved, right? This is at least what the search function returned...
I find it unlikely that the diesel filter would be clogged after only 50,000 km, as the replacement should be done every 60,000 km (or was it only 30,000 km? ).

Regards,
Hermann.

- Diesel filters are typically replaced every 30,000 km (replacing them helps with troubleshooting and never causes any harm).
- The injection start timing regulation is (at least in my 1Z engine) very tolerant - at idle, it's constantly at the limit, and still off by 4 degrees! - without any error codes).

- It's easier for air to be drawn in than for diesel to be pushed out, so "no diesel drips" is not proof of tightness.

The sealing ring under the diesel pre-filter membrane (the bump on the filter) is prone to leaking, or the retaining spring may no longer provide sufficient pressure.

The air bubbles are definitely NOT normal, I would say, and I would try to get rid of them.

However, they shouldn't directly cause stuttering, because they rise up in the pump and are unlikely to reach the high-pressure side.

m;

Thank you, Martin.

That was roughly what I had in mind.
A new diesel filter has been purchased and will be installed early next week; it's a requirement when replacing the fuel pump.
Okay, then I'm going to replace the seal on the filter valve as well.

Regards,
Hermann.

I also have various air bubbles passing through the inlet hose. I actually thought this was normal. Until recently, the engine has been working perfectly, but last time it ran on only 3 cylinders for a short period s. here. Is that related?

Regards,
mcgregg

@Mcgregg

I think 2 minutes is too long for "air in the HD cable."

I've only replaced the filters on my fuel injection nozzles for the combustion chambers so far. But once they've been used, the engine immediately runs smoothly on all cylinders. Previously, it was common practice to play the organ for extended periods (using all the stops).

I probably would have given him a few gas shocks if he was playing with three cylinders. If something immediately solves the problem, don't think about it any further.

m;

dieselmartin wrote:

@ Mcgregg I think 2 minutes is too long for "air in the HD cable." I've only replaced the filters on my fuel injection nozzles for the combustion chambers so far. But once they've been used, the engine immediately runs smoothly on all cylinders. Previously, it was common practice to play the organ for extended periods (using all the stops). I probably would have given him a few gas shocks if he was playing with three cylinders. If something immediately solves the problem, don't think about it any further. m;

At first, I hesitated to use the gas pedal. But then I decided to be brave and pressed the gas pedal further, and everything went back to normal. Since then (approximately 10 starts, over 200 km), I haven't noticed any unusual behavior.

I will try not to think about it. Even if it's difficult.

Hello,

I switched three weeks ago from a Golf 2 Diesel (432,000 km) to an Audi 80 B4 TDI Avant (351,000 km), and I've been struggling ever since with the - until then unknown to me - jerking.

"I also had a lot of air bubbles in my Audi. The leak was caused by the brass sleeves that are pressed into the aluminum of the diesel filter adapter and to which the diesel lines are attached." After replacing the adapter (my dealer sold me a complete unit - adapter and filter), the air bubbles are gone.
Smile.
The itching - I thought it was due to the blisters - unfortunately, has remained with me.

MichaelJ

@michaelj

Thank you for the tip about the brass sleeves. I'll take a closer look at that.
The filter will definitely be replaced, along with all the hose connections and all the fabric return hoses.

I'm curious to see what happens.

Regards,
Hermann.

dieselmartin wrote:

However, they shouldn't directly cause stuttering, because they rise up in the pump and are less likely to reach the high-pressure (HD) section.

Hm - sort of

At the moment when an air bubble passes through the outlet nozzle of the pump housing, the internal pressure of the pump will more or less collapse.
Following: The injection timing is shifting in the "late" direction, and the injection start control system is attempting to compensate for this (provided the control range is sufficient).
Meanwhile, the air bubble has disappeared, the internal pressure of the pump is returning to its normal level, and the injection adjustment jumps forward, once again causing the control system to become erratic...

So, I can definitely imagine that constantly ingested air bubbles could cause some kind of jerky-like phenomena.

That makes me happier now.
Would the ordered filter already be here ?

Hermann.