Not a lot of boost, no fault codes, no obvious leaks on AAN

[LitD]

Hi all,

Quick reminder, my UrS4 stopped boosting and was throwing a 561 fault code. I've boost tested my car with the help of bilko and we couldn't find any obvious leaks. We also read the faults off the 'engine' section of VAGCOM and the only error was the standard one about the engine speed sensor. I also floored it on the way home and the built in boost gauge was reading 1.9 bar. So I have a couple of questions:

1) How accurate is the internal boost gauge (i.e. if it says I'm getting boost, am I actually getting boost)?
2) Where is the sensor for the boost pressure located in the intake system?

Pressure testing procedure was as follows:
1) Remove MAF to turbo hose and insert bung
2) Remove Breather pipe from the cam cover and insert bung
3) Spray soapy water on all the pipes we could see
4) Apply 20psi to the system (from a tyre) and look for bubbles/listen for leaks.

The only hose we didn't check was the T pipe under the intake manifold. Any constructive comments on the pressure testing we did and any suggestions of things we might have missed/next steps?

Thanks

Rob

[LitD]

I had a brainwave on the way to the shops. What are the symptoms of a stuck open wastegate?

[Rusty]

What's it supposed to boost to?

[LitD]

Right, well the brainwave is wrong cause if the wastegate was stuck open it wouldn't generate any boost at all, right?

Rusty, as far as I know it's completely standard, however I know the wastegate was sticking before I bought it and the previous owner sent it off to turbo technics to get it fixed. I'm not sure if he had the spring done on it at the same time. I'd presume not though.

[UrS4boy]

I really doubt that you had the air volume and pressure to get 20 psi in the intake tract using a tire as the source. I you did, good on you and I learned something. Otherwise, I would say you haven't really tested the intake tract.

The 00561 code is as follows:

"•2413 (Blink Fault Code), 00561 VAG1551/2 Fault Code Number
Mixture Adjustment,
Adaptation limit exceeded, Adaptation limit not reached, Leakage in exhaust system before 3 Way catalytic converters, Incorrect signal for Mass Air Flow Sensor, Spark plugs, ignition coil(s), or Ignition Coil Power output stage malfunctioning
Symptom: Rich mixture, increased fuel consumption"

The OE digital boost gauge displays absolute pressure, i.e. atmospheric pressure plus boost (or minus vacuum). So 1.9 Bar = about 0.89 Bar relative boost = lower than it should be, i.e. you have a small boost leak somewhere.

The ECU reads the manifold pressure via the G71 Manifold Absolute Pressure (MAP) sender in the ECU. (Check this link: http://forums.quattroworld.com/s4s6/msgs/20417.phtml). Your UrS4 came with a 250 kPa (2.5 Bar) MAP sensor. If it was changed to a 300 kPa (3.0 Bar) MAP sensor, the OE digital boost gauge display readings are wrong.

[LitD]

UrS4Boy - Yeah, the 20psi thing reads wrong. I meant a tyre inflated to 20psi was attached to the intake track. What sort of pressure would you put into the tyre to properly test the intake then?

[UrS4boy]

UrS4Boy - Yeah, the 20psi thing reads wrong. I meant a tyre inflated to 20psi was attached to the intake track. What sort of pressure would you put into the tyre to properly test the intake then?

Okay that confirms that you haven't tested the intake tract properly (IMO) and that you need to attach a compressor to the intake testing bung (presumably you are using one with a Schrader valve or a quick fit air line connector, like this one (below)). I would run the compressor pressure up to 10 psi and then 15 psi. No higher than 20 psi.

This link shows some typical boost leak locations:

http://forums.quattroworld.com/s4s6/msgs/229230.phtml

[LitD]

Cool. We only had the tyre available as a pressure source hence using that. Right, time to go hunting for a compressor then.