Warhead

At WOT you should be making boost, not pulling a vacuum. (at wot your gas pedal should be to the floor)

you say the hissing noise is more noticeable when then engine is under load (producing boost). but you only hear it at 20+psi? or do you hear it right from 0psi all the way to your peak/max boost pressure?

If you only have a hissing sound at 20psi or more, then I would guess its a small boost leak (maybe a clamp is a few turns loose?) I you hear it all the time it could be a larger leak, or even a small exhaust leak.

to answer your questions

1: yes in theory the higher the psi the louder/ more noticeable the leak. But leaks don't always work as such.

2: vacuum leaks are much harder to hear, but they often show them self in the car not preforming properly. But here from what I am gathering is you don't have a vacuum leak as your numbers seem to be in order.

This is very hard to do over the internet too, is there anyway for you to take a video of the sound? are you able to replicate it while the car is not moving?

I don't know how in depth you went with trying to find the leak, but an easy way to find it would be to use a boost leak tester (you can make one for about 20$) you just need an air compressor. it allows you to add psi to your charging system (so you could set it to 20psi) and find any and all leaks you may have.

Note: have you looked at the clamps on your FMIC? or inspected the FMIC itself?

apoelistas

Thanks for your kind explanation. I misunderstood the WOT.
WOT it can reach 30-35 psi boost.

Answer:
CORRECT but never at 30 or 35 psi (boost).



when not moving I cannot replicate the hiss sound. When driving without depressing fully the acc pedal I have no hissing sounds.

​​​​​​I wanted to make sure that I have a vacuum or a boost leak before examining further. I have not checked the intercooler pipeline yet or pipeline near the turbo.

Audi could not find the leak after spending one hour. They want 2 days for examination. They don't seem to have a smoke tester. They have replicated the hiss sound.

My mechanic, who services my other cars, does not have experience with turbos. He does not have a smoke tester or the modified pipe part for the pressure test.

A friend who has a Subaru WRX and goes to races told me to get vacuum and boost readings and find out if hissing is caused by boost or vacuum. Preferably to install a boost/vacuum gauge.

Then I remembered that I had a diagnostic (from usa) which measures boost and vacuum.

Procedure :
1. Check exhaust for leaks due to good boost and vacuum readings.
2. Upgrade intercooler and check /inspect pipelines at the same time. I was waiting to find the cause before changing intercooler but I think it is best at the same time.
3. From this exercise it seems that I dont have a vacuum leak.
4. I may have a turbo boost leak due to noise when on boost, though when on high boost 30-35psi I don,t get the hissing sound.Need to check boost pipeline.
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I have never done a boost test so I don't know the procedure. I was thinking of using my old telephone in the engine to record the sound. would this help????

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apoelistas

As part of the investigation, as a precaution I will change 1 & 2 below (seeing the intake vacuum system diagram)
1. 058 905 291 B non return valve
2. 06H 133 781 CB hose with non return valve (this I will not change yet because it is expensive and probably if this would fail I would get DTCs)
3. 8R2 611 931 A vacuum hose with non return valve.
4. Will try to find the adapter for carrying out a boost leak test, since it must be the boost that is affected, as discussed above
5. Check if coils are correctly seated
6. Check intercooler pipeline, post turbo. Audi will do this in my next visit after calling them.

I think I found APR selling one for Q5. Will order one ASAP. DT100001 (universal hose with regulator) DT100003 (adapters).

MSQ5

Forgive my ignorance, but are you sure you are hitting boost of 30-35 psi, too? I don't have the 2.0T, but thought:

1. It uses the small K03 turbo targetting something a bit under 14 psi or so on stock ECU mapping.
2. A K03 and even the larger K04 on my Mazdaspeed 3 cannot sustain boost over about 18 psi at high rpm WOT under load without rapid internal damage due to friction induced heat that'll rise well above 1500 degrees F. and damage the center shaft. It just makes heat past 19 psi or even 16 psi at redline.
3. 30-35 psi boost will blow most stock engines unless they are race built with forged internal parts and very strong I beam type connecting rods.
​​​​​​​I am seeing 19 psi max under load with 93 octane (US) pump gas on an ECU reflash tune that tapers to about 15 psi at redline, and that is all a K04 can handle. A K03 less so.

apoelistas

I had my ecu reflashed with the latest 2016 firmware for the oil consumption and PCV replaced with latest PCV revision (TPI 2024604/28) Is this firmware same as the facelift firmware which produces 225bhp?? My Q5 prefacelift is suppose to produce 211bhp.

Taking a screen shot is difficult but I can shoot a video if you wish of my obd boost reading at readline. I will have this ready tomorrow night.

Before flash: 8R0907115A 0004
After flash: 8R0907115R 0002

Do you think my turbo is over boosting?? Is there a reason that would cause this to occur??

apoelistas

Confirmed
FL_8R0907115R__0002.frf (this firmware is in flashdaten and FL means facelift).

Audi flashed my firmware with the 225 bhp firmware.

So it seems that my turbo is overboosting (in order to reach peak power of 225bhp??). I definitely need to change my intercooler to larger to reduce heat if this assumption is correct.


I am not sure if my diagnostic can calculate peak power too, but even if it does, I don't know where to test this.


Also I believe when at high revolutions at readline my boost drops. It cannot sustain more than 20 psi I believe. Not sure if I can video both instrument cluster and boost/vacuum at the same time.

MSQ5

You probably have a leak on the post turbo side of your intake system but I have no confidence in the readings you are reporting from your OBD 2 port. What monitoring software are you running?

Please stop chasing the problem with throwing more stuff on the engine. You need to identify and resolve the issue. Boost is likely to taper toward redline as I explained earlier.

​​Is your car presently purely stock? What have you done to it?
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apoelistas

Cheers. I will check the post turbo side. Yes my car mechanically is purely stock. So I should check the pipeline as diagram below??


The diagnostic is obdlink SX (usb). The android app is free from app store from manufacturer.

At readline I have less boost. I will use tiptronic and test again. Which gear should I choose to test the boost at readline or does it not matter e.g 2 or 3 or maybe 4th??? I need some guidance in order to produce correct results.

apoelistas

I spoke with a friend, after MSQ5 asked the questions above about my boost pressure incorrect data. obdlink measures psi above 1 atm. Which means we have to subtract 1 bar boost or 15psi (14.5 actual).

So my car can reach 35-15 psi = 20psi boost. (though usual is 15psi).

obd readings should be corrected by 1 bar or 15 psi. First time use so I did not know.


Using the altitude pressure formula correction, above sea level, true actual value is 14.3 psi correction (not 14.5 as stated by my friend).


Will try to check if I can enter this value in the obd2 settings

MSQ5

Subtracting atmospheric pressure, approx. 14.5-14.7 psi makes sense for your app. That produces numbers that are appropriate for the turbo.

Yes, check all of the couplers and any small hoses going to the bypass or diverter valve.