TDI 90PS Performance Issues: Part 2

Hello everyone,

I already reported about my problem in this forum a week ago. Thank you again for the help.

In the meantime, the condition has worsened to the point that the car can only reach 120 km/h. Accelerating is an adventure, even at low RPM. Usually, the car goes into limp mode around 3600 RPM. As I mentioned before, I'm measuring between 1.5V and 3.5V on pin 5 of the mass airflow sensor, which should be okay. Looking back, I have to say that the problem has been gradually getting worse, not suddenly.
The last time I heard from Markus, among other things, he suggested that the turbocharger wastegate solenoid valve might be a potential source of the problem.
Okay, here's the translation:

'Now, my question: If this solenoid valve is defective, could that also be the cause of my lack of power at low RPM? How can I test this solenoid valve before replacing it, and what kind of failure would it cause if it's defective? Does anyone have any other ideas?'

Best regards, Franz.

The faulty magnetic valve causes the engine control unit to switch to emergency mode, which usually happens at high speeds and under heavy load. After that, the engine remains in 'emergency mode' and runs like an SDI, with very little torque. If you turn the engine off and then restart it, everything is normal again until you reach high speeds under the same load. I've experienced this problem four times and always keep a spare part on hand.
If that could be the problem, you could try replacing the valve; it costs about 25-30 euros. And if it wasn't the problem, it's always good to have that part on hand!

Hi,

Actually, a new valve costs less than 30 euros.

If you would prefer to test the solenoid valve first, you will need an ohmmeter.
Then, you unplug the connector at the valve.
You connect the ohmmeter to the terminals of the valve.
For a 1Z engine, the values should be between 25 and 45 ohms.
If that's not the case, the valve is defective.

The problem, if my memory serves me correctly, is that you weren't entirely sure whether you had a 1Z engine.
That's something that's really important right now.

Furthermore, a faulty power supply could also be the cause of the malfunctioning solenoid valve. Therefore, check things like the wiring.
And - very simply - are all the hoses attached to the valve?

MARKUS.

Hi Markus,

I've already checked the solenoid valve for continuity – it had a very low resistance. I don't remember the exact value, but I can check it again. Is it possible for the solenoid valve to be defective in its valve function, even if it's electrically okay?

Best regards, Franz.

Hi,

It's best to double-check the part again, as you mentioned. If you're certain that you can't achieve the specified Ohm values, then the other questions become irrelevant, and you'll need to replace it.

Regarding your question (the electric valve is okay, but still broken), I'm afraid I can't offer any assistance.
And then, for me, the rule is: If you don't know something, just keep your mouth shut...
But I'm sure others know more about that!

Hi,

The components operate by using a pulsed magnetic field to hold an iron core in a suspended position. This switches between a vacuum and a normal pressure state, which ultimately provides the control pressure for the can.

Even if the component is electrically sound, it can still get mechanically stuck.

Best regards,

Jan.

Hello,

I just checked the solenoid valve with an ohmmeter - it's measuring around 25 ohms. This exactly matches the values Markus reported. I also checked the power supply - with the engine running, I disconnected the solenoid valve connector and measured 5.8V. As soon as I plug the connector back in, I get about 1V at the connector. This is quite strange. There should be 12V there. At what RPM does the valve switch?

Best regards, Franz.

"In my case, the turbocharger's wastegate valve was also defective. I first performed all the electrical tests (resistance and voltage), and those were fine. I was getting 12V."
After that, I connected the 1551 and performed an actuator diagnosis, which showed that it was not working.
So, I bought a new one for 29 € and now everything works again .

Regards,
*Mario

Hi Franz,

I would like to refer to my diagrams once again.

When idling (which it isn't doing in this case), the valve is controlled with a duty cycle of 24% (in the ASV mode). You might see something in the range of 1 to 4 volts, depending on how slow the multimeter is. The voltage fluctuates between 0 and 12 volts, regulated by the duty cycle. The above 24% means that it is 12V for 24% of the time, and 0V otherwise.

If you disconnect the plug, the boost pressure will likely increase slightly even at idle (because you've deactivated the control), causing the engine control unit to try to compensate. To do this, it will increase the duty cycle significantly, which you will then see as 5 volts or more. Since no reaction occurs despite this change, it will (presumably!) stop trying and write an error to the log. If you have VAG-COM, follow measurement block 11 during this process; I think you will find this exact reaction there, specifically in the duty cycle.

Based on your measurements and this explanation, I would conclude the following: The control unit is functioning correctly and is controlling the valve in a perfectly logical manner. Since you don't have a short circuit (0 ohms) or an open circuit (infinite ohms), the valve's coil is likely also okay.

So, what remains: either a mechanical blockage in the valve, OR difficulty in adjusting the turbocharger. If you've ruled out the latter (by testing with a syringe or similar), then replacing the valve might be a worthwhile attempt.

Best regards,

Jan.

Hi Jan,

Your explanations were quite helpful. The magnetic valve seems increasingly likely to be the problem. I'm also not hearing any clicking or similar noises. I'll get a new one and also replace the vacuum hoses while I'm at it. The test is definitely worth it. I'll report back immediately after the test drive. I'd like to thank everyone for the tips so far.

Best regards, Franz.