Diesel Filter: Causes of Engine Surging?

A friend of mine has a Vento, and the diesel filter has been in there for about 60,000 km (!) without being changed or drained. We drained it yesterday (because his car has been running rough and has a pulsating idle), but the rough running didn't improve. When driving at 100 km/h on a country road, the car accelerates slightly, then slows down again, and this happens constantly. It's obviously very annoying. It can't be the fuel injector pump, because it brought the car up to about 3,000 rpm, and there were no misfires when I tapped on it. Could it be related to the diesel filter? I've already used the search function, but I haven't found anything useful.

Best regards, WarLord.

Hi Warlord,

I had a similar issue with my Golf once. I replaced the turbocharger boost control valve, and it worked. It costs around 30 euros, the part number is 028 906 283 F, and everything was fine again.
It can also have other reasons; this has been described several times in this forum before, the keyword being "wave-like acceleration."
So far, I haven't experienced these symptoms due to a clogged diesel filter.

If the problem is with the diesel filter, the car usually doesn't have its full power.

However, the timing belt should be replaced (or have it replaced) based on mileage.

Otherwise, I would suggest having the error memory read out.
If that doesn't work, perform a test drive while connecting a VW diagnostic tool to check the actual values/input signals.

@Snowman

I thought the same thing at first. The relay also makes an odd clicking sound. However, the relay in my 1Z now clicks irregularly when it's cold, and mine doesn't accelerate in a wave-like pattern. Furthermore, we once disconnected the relay (electrically), and even then, it still accelerated in a wave-like manner or behaved in that way.

@Martin R

'The error codes are being read, and I've advised/will be replacing the part. I'm not sure what to make of the performance claims. My loader engages more abruptly; you don't really notice the engagement with the Vento. Also, it seemed to me that the Vento wasn't accelerating as strongly as my Passat (and that's saying something).'

Best regards, WarLord.

WarLord wrote:

(because his car always drives in a wavy manner and has a rumbling idle)

Hi WarLord,

Have you already checked the timing of fuel injection, ignition timing (including the distributor), and the fuel injection volume? A rumbling idle doesn't sound like a clogged fuel filter!

@warlord

Use the search function and type in 'ruckeln'. You will find a huge amount of information on that topic! }

@haehnlein

I haven't checked the fuel injection volume or the start of injection yet (I need to take it to the workshop for that), but the crankshaft bolt is already the 12.9 grade. However, I also noticed something: The engine makes a knocking sound compared to my 1Z (which doesn't make any noise) when the hood is open.

@joergs

I've been looking into 'stuttering' or 'jerking,' but I wasn't sure if that's what it is. Ulf, for example, defines 'stuttering' as misfires, and this car doesn't have any misfires (the fuel injector is working perfectly).

Best regards, WarLord.

@warlord

It's definitely glitching! I think there are enough potential sources of error and enough written material to cause it. Just keep digging, and you'll find the problem! You should also consider getting a diagnostic system. Without one, it will certainly be difficult.

joergs wrote:

It's certainly bumpy!

I think there are enough sources of error for that. }
Hmm, I understand "jerking" and "wavy acceleration" as completely different phenomena, even just in terms of their "frequency":

"Jerking" refers to more than 1 cycle per second (e.g., the "oversized pump setting jerk" with an estimated frequency of 3-5 Hz).

Wavy = 1 cycle per second or slower.

For the problem discussed here, I would consider a sticking injection nozzle adjuster as a possible cause.

If the adjustment can only be made in steps of, for example, 3° KW, then, in my opinion, this could explain both the wave acceleration and the rumbling idle.
When the injection start control system attempts to reach the target value, and the injection start suddenly jumps forward or backward by 3°, the motor speed will initially try to increase or decrease accordingly, but this is regulated before significant speed changes occur.
What remains is a sort of rumbling.

It should be easily checked with VAGCOM (observe the start of injection at idle), or by measuring the likely voltage of the fuel injection timing control valve.

Hmm, this is getting interesting. This must be related to the injection start and timing. The start isn't great (it's initially pushed by the battery), and after the start, there's also a lot of smoke coming from the exhaust. Could that rumbling noise be related to that? Also, there's hardly any torque immediately after the start; it takes a short moment for it to rev up, and that happens very slowly. After that, it's okay, although not as responsive as my TDI. Oh, and the thermostat seems to be broken too; the engine barely reaches 90°C, and when you turn on the heater, the temperature drops too much.

Best regards, WarLord.

It's certainly bumpy! I think there are enough sources of error for that.
Hmm, I understand 'jerking' and 'wavy acceleration' as completely different phenomena, even just in terms of their 'frequency':

'Jerking' refers to more than 1 cycle per second (e.g., the 'oversized pump setting jerk' with an estimated frequency of 3-5 Hz).

Wavy = 1 cycle per second or slower.

For the problem discussed here, I would consider a sticking injection nozzle adjuster as a possible cause.


It could also be. However, in my opinion, it's difficult to distinguish between 'stuttering' and 'wavy,' and the boundary between the two is hard to define clearly.

if I see warlord's new post, then I don't think it's a fuel injector problem. It looks more like a misconfigured fuel pump, which could be causing this wave-like acceleration or whatever it is. The system is constantly adjusting, sometimes in one direction and sometimes in the other.

joergs wrote:

if I see warlord's new post, then I don't think it's a fuel injector problem. It looks more like a misconfigured fuel pump, which could be causing this wave-like acceleration or whatever.

Because the system is constantly adjusting, sometimes in one direction and sometimes in the other.
Hi Jörg,

Let's wait and see what the more detailed inspections reveal. *fence post angle for warlord -> post!*. Both of these should be easily identifiable with VAGCOM.

Okay! Everything is a bit vague and can only be interpreted with a lot of guesswork!

Let's wait and see what the more detailed investigations reveal *fence post corner for warlord -> post!*. With VAGCOM, both should be easily identifiable.

I'll try to post something. Unfortunately, I don't have a VAGCOM or a diagnostic adapter. A friend might be able to get access to an etching machine and etch a circuit board for me. However, I'll be taking the car to the workshop next week, and then we'll see what happens.

@joergs

Injection rate controller? Is that the flow rate adjuster?

Best regards, WarLord.

WarLord wrote:

Spritzversteller? Is that the quantity adjustment device?

Oops. . . hopefully Rainer won't kick you out because of that and ask you exactly that kind of question for the re-admission exam. . .