Stuttering in 1Z: Troubleshooting Guide

I have a Volkswagen Passat with engine code 1Z, 90 horsepower, manufactured in March 1994, currently showing approximately 30,800 kilometers, but the actual mileage is around 140,000 kilometers.
My problem: my engine has the well-known issue described and discussed in this forum, which is jerking during acceleration. I've been to 4 workshops, but the error hasn't been found. Replacing the control unit, mass airflow sensor, and throttle position sensor didn't solve the problem. Two weeks ago, the ELAB was replaced, and the car ran perfectly for a week. Last Monday, it couldn't be started with the powerbox activated, only without it. Today, I drove it again as a test and noticed the following: The car runs completely normally (now again with the powerbox), but when accelerating out of right-hand curves at speeds above 40 km/h, it starts to jerk briefly, as if fuel is missing or being displaced by centrifugal forces. It sounds funny , but it's not.
'It works perfectly fine on straight roads and in left-hand curves. Can anyone give me some advice, especially from experienced people?'

Hi.

For such vague error symptoms, start by reading out the fault memory (or having it read out).

Doing it yourself ensures that no entries deemed "inconvenient" for the workshop are brushed aside – which unfortunately seems to be a common practice in order to distract from one's own lack of knowledge .

That means that if you're taking your car to a workshop, it's best to choose one where you can be present or where you truly trust the staff.


The mileage and year of manufacture made me worry that your car...
a) still features a wear-prone resistor adjustment mechanism, and...
b) this could be worn out.

DIY test:
Hold the ohmmeter between pump cable 1 and 2. If it displays a reading of approximately 6 ohms, then that's the better inductive sensor.
Significantly higher readings (above 50 ohms) indicate a problem with the potentiometer. I don't know how much it would cost to replace it, or whether the entire pump needs to be replaced...

At a well-equipped Bosch diesel service center, you can have a hysteresis measurement performed, which will provide information about the condition of your potentiometer for slide range adjustment.
It should cost around 50 EUR.

edward wrote:

At a well-equipped Bosch diesel service center, you can have a hysteresis measurement performed, which will provide you with information about the condition of your potentiometer for slide range adjustment. It should cost around 50 EUR...

Hi Edward,

This measurement still seems a bit mysterious to me... does it really only apply to the old potentiometer, or also to inductive sensors?

Regarding only the stiffness of the switchgear mechanism (which is precisely what's being measured, and nothing else), it can also be tested independently:

Remove the pump cover (possibly emptying the pump partially beforehand) and rotate it at the measuring ring. Although a spring pushes the ring against its zero position, it should move freely and smoothly, compensating for the spring force. At most, it might feel slightly stiff in the upper quarter (where the pump is not normally operated).

And the shaft should have absolutely no play; approximately 0.5 mm of axial clearance is considered normal.

ulf wrote:

... This measurement still seems a bit mysterious to me... does it really only apply to the old potentiometer, or also to inductive sensors? ...

...also applies to the inductive sensor as well...

Quote:

... Regarding only the stiffness of the switchgear mechanism (which is precisely what's being measured, and nothing else), it can also be tested independently: ...

Apparently, recognizing this fact is not as simple as it seems.

Quote:

... Remove the pump cover (possibly emptying the pump partially beforehand) and rotate it at the measuring ring. Although a spring pushes the ring against its zero position, it should move freely and smoothly, compensating for the spring force. At most, it might feel slightly stiff in the upper quarter (where the pump is not normally operated). And the shaft should have absolutely no play; approximately 0.5 mm of axial clearance is normal.

... the spring force should not be underestimated in this case...
For this test, it's important to have a good reference pump for comparison.

Hello everyone,
Thank you for all the answers. I'm currently under a lot of stress at work and won't be able to have the error codes read until Thursday. I performed the measurement of my throttle position sensor according to ULF's instructions. The value is 6.2 ohms, which means I installed the inductive sensor. In the meantime, the car is running again because I loosened, untangled, and properly reattached all the ground cables at the battery terminal, and also cleaned every connector (3-pin engine speed sensor, 8-pin throttle position sensor, 2-pin needle lift sensor) with contact cleaner. I thought the problem was due to a faulty cable or a bad connection. So far, it's been working, and I will report any error messages as soon as I have them.

Regards,
old-Austrian

old-ösi wrote:

In the meantime, the car is running again because I... cleaned every connector (3-pin engine speed sensor, 8-pin throttle position sensor, 2-pin needle lift sensor) with contact cleaner. I thought the problem was due to a faulty cable or a bad connection. So far, it's working, and I will report any error messages as soon as I have them

.

Hi Austria!

If your contact spray happens to be of the aggressive variety, you may have inadvertently installed a potential time bomb .

This type of cleaner not only cleans, but also corrodes contact materials over time.

To salvage what's possible, I would re-examine all the connections that have been addressed.
Rinse thoroughly with plenty of degreaser.
2. Then, saturate with spray oil that should have instructions like "does not damage common materials."

@ulf:
I don't believe that a hysteresis measurement only measures the spring travel of the control slide. In my opinion, an ideal spring should not exhibit any measurable hysteresis curve, as this would compromise the ability to precisely reproduce the spring position. As you probably know, a hysteresis curve consists of two adjacent S-shaped lines that only 'jump' to each other when the maximum value is reached. However, in the case of the control slide, at least with regard to the spring, the same curve should always be traversed.
Therefore, I believe that the H-measurement also includes the inductances or associated resistances of the potentiometer.

Am I right about that? Maybe there's someone out there who knows about it :-).

edward wrote:

@ulf: I don't believe that a hysteresis measurement only measures the spring travel of the control slide. In my opinion, a hysteresis curve should ideally not be measurable in a spring at all, because otherwise, a precisely reproducible spring position cannot be guaranteed. As you surely know, a hysteresis curve consists of two adjacent S-shaped lines that only "jump" to each other when the maximum value is reached. However, in the case of the control slide, I believe that – at least with regard to the spring – the same curve should always be traversed. Therefore, I believe that the H-measurement also includes the inductances or associated resistances of the potentiometer. Am I right about that? Maybe there's someone out there who knows about it

.

That's exactly what it's about... absolutely right!!
This allows for the determination of potential difficulties in operating the signaling system.