Low Pressure: Only 0.6 Bar - Troubleshooting

hi...

After installing a boost gauge, I realized that I'm only getting 0.6 bar of boost pressure instead of the expected 1 bar.

Initial suspicion was a VVT (Variable Valve Timing) issue... but everything checked out to be okay.

I'm now suspecting it's the solenoid valve... or is it? Now my question: With VCDS (VAG Com), you can display the actual and target boost pressure... but what does the 'duty cycle' value represent?

best regards...

Which car and engine code?

We can't predict the future yet...

Sorry, I forgot.

Golf III, manufactured in 1997, engine code: AFN... I just thought that this might not be essential for explaining the gear ratio.

BlauBaer wrote:

sorry...forgot... Golf III, manufactured in 1997, engine code: AFN... I just thought that this might not be essential for explaining the gear ratio

.

If you have a 1Z engine with a Watstegate turbocharger, the explanation is different compared to a VTG turbocharger. One operates with overpressure, while the other operates with underpressure.

The duty cycle specifies the type of rectangular signal used to control your charge pressure control valve, which regulates the vacuum pressure for your VTG (Variable Turbine Geometry).

(here is the explanation for 1Z:)
The duty cycle indicates the type of rectangular signal used to control your boost control valve, which regulates the overpressure for the wastegate.

The duty cycle indicates something about the on and off times of the voltage, i.e., the ratio of on time to off time.

@ Bertil

For example, with the 1Z system: When the solenoid valve receives voltage, does the pressure sensor experience overpressure? Or when the solenoid valve is de-energized?
Does the solenoid valve receive continuous voltage when the duty cycle is 100%?

Sorry for the silly questions, but I really want to understand this properly.

Thank you.
David.

DocSnydor wrote:

@ Bertil For example, with the 1Z system: When the solenoid valve receives voltage, does the pressure sensor experience overpressure? Or when the solenoid valve is de-energized? Does the solenoid valve receive a constant voltage when the duty cycle is 100%? Sorry for the silly questions, but I would really like to understand this properly.

Hi.

subject to Bertil's answer as a former 1Z tamer :

"A 100% duty cycle in VAG systems, as far as I know, strangely means that the valve is completely de-energized (0% --> constant battery voltage)."

When power is lost, the valve in the 1Z engine releases the full boost pressure to the wastegate actuator, causing it to open at approximately 0.6 bar and limit the boost pressure.

As the pressure increases, the valve reduces the pressure for the wastegate, causing it to open later and thereby achieving a higher boost pressure.

BlauBaer wrote:

hi... After installing a boost gauge, I realized that I'm only getting 0.6 bar of boost pressure instead of the expected 1 bar. Initial suspicion was a VVT (Variable Valve Timing) issue... but everything checked out to be okay. Now, I suspect it's the solenoid valve...or is it? Now my question is, with VAG-COM, you can display the actual and target boost pressure...but what does the "duty cycle" that's displayed mean?

Hi.

It could be a solenoid valve, but it doesn't necessarily have to be. Alternatively, it could be clogged vacuum hoses or a worn vacuum pump. Or there could be a crack in the control hose leading to the turbocharger.
Air leakage into the vacuum chamber (a sphere to which an extra hose is connected behind a "one-way valve") can cause similar effects.
Without vacuum, virtually no boost pressure is generated in the AFN system.

With a pressure of only 0.6 bar, whereas approximately 1 bar is "desired," the duty cycle should be close to zero according to VAGCOM, or the voltage at the solenoid valve should be in the range of 11-13 volts when measured with a voltmeter.

ulf wrote:

subject to Bertil's answer as a former 1Z tamer :

... Class expression ...

Quote:

"A 100% duty cycle in VAG systems, as far as I know, strangely means that the valve is completely de-energized (0% --> constant battery voltage)."

... Yes, that's correct. The reason for this is that, without electricity, the boost pressure should not exceed the wastegate pressure.

Quote:

When power is lost, the valve in the 1Z engine releases the full boost pressure to the wastegate actuator, causing it to open at approximately 0.6 bar (?), thereby limiting the boost pressure.

... it's only been two weeks, but 0.6 bar is correct.

Quote:

As the pressure increases, the valve reduces the pressure for the wastegate, causing it to open later and thereby achieving a higher boost pressure.

The wastegate receives a metered amount of boost pressure, which effectively "falsifies" the actual pressure reading (which is only known to the engine control unit - hopefully).

Thank you, Ulf...

@ Bertil, Ulf

Thank you for the well-explained explanations! I can use this to make good progress in the endless search for solutions when troubleshooting the 1Z. }