Yet another 1.8t AGU with no boost

[dcjk]

Hey guys,
I've got this A3 1.8T AGU as a project car. I know that it would've been better to get something equipped with ME7.5 instead but.. it is what it is

The problems I'm having with it are:

1. Doesn't boost enough (goes up to 0.1bar)
2. RPMs are not stable at idle (it bounces between 900 and 1000rpm)
3. Doesn't start from the first time when there is less fuel in the tank (once the fuel lamp comes on)

Until now I've discovered that the following has been replaced/fitted:

1. I believe it is fitted with a AUM turbo (JPG 1117400800, which according to the catalog fits as a replacement for 06A145713F)
2. Silicone TIP
3. Vac lines replaced with silicone ones.
4. Forge 007p
5. Boost gauge

I've done the following:

1. VCDS scan (showed no errors)

• MAF measures 2.36 g/s at idle
• Lambda reg value shifting between positive and negative (-7.0% to 7.0%) at idle
• N75 shows 99% duty cycle at full throttle

1. Inspected the TB (didn't need a cleanup)
2. TB adaptation
3. Cleaned the MAF sensor (no difference)
4. Have checked the vac lines for leaks (no bad lines)
5. Tested the FPR (holds vacuum)
6. Measured the fuel pressure (2.4bar at idle)
7. Tested N75 (works properly)
8. Wastegate seems to sit closed
9. Couldn't find any other leaks
10. Measured all 4 injectors with a multimeter (12.4 ohm)
11. 2 of the injector inserts looked "oily" so I ordered 4 new ones, but I don't think that could be the cause.

Unplugging the MAF sensor made no difference, not sure if that's "bad MAF" indication". Also unsure if it has been mapped at this point.

 

[desertstorm]

I would suspect a hole in a boost hose or intake system somewhere. That's why you have no boost and idle is all over the place. A smoke test will usually show up the leaks.

 

[dcjk]

Thanks for the suggestion, had the time to do a smoke test today and found two small leaks (fortunately it was an easy fix for both of them, more pressure testing and smoke testing didn't show other leaks) I also tested for leaks around the injectors with soapy water (all good there).

So the boost is tiny bit better but still not what it suppose to be (3rd gear 6k RPM boost= 0.15bar), the RPMs are still going a bit up and down. I am not sure what else is going wrong here, one more thing I've noticed when accelerating is some strange sound which is kind of hard to explain but it sounds like "tststststtstsst", unfortunately it can be heard only while driving, didn't manage to recreate it otherwise.

 

[b2]

Unplug the pipe from the n75 going back to the wastegate actuator and see if it boosts to the moon. If it does the n75 is knackered, if it doesn't your wastegate or turbo is fubar.

 

[dcjk]

I've tried unplugging it in the past and there was no difference, I also tested the wastegate and it functions as it should. Hard to believe the turbo itself is bad as there is no smoke whatsoever but I might be wrong on that.

 

[b2]

When my cars K03S failed it did not boost plus my car did not smoke. Diagnostic tests showed everything was fine and there was no fault codes! When I disconnected the wastegate actuator pipe to the n75 my car never boosted either. I tested the N75, MAF, MAP, duty cycles, fuel pump, amongst other things and was going round in circles, in my case the penny valve had broken off inside the turbo and I was getting no boost! I changed the turbo and hey presto I was up and running like a good un.

 

[dcjk]

b2, thank you for the suggestion. Not sure why but I never though that the penny valve might be the issue (simply because I was told that the turbo has been driven 3k km from new).
Your post got me thinking that maybe the penny valve doesn't sit closed, and guess what...it didn't. What I did was remove the "nut lock" (not sure how it is actually called) then loosen the upper nut and tried to move the flap by hand (not forcing it too much), so it moved like 4-5mm up the rod (I already had a smile on my face by that time ) then I tightened the second nut and put back the "nut lock", so that was all.
Car boosts 0.6 bars now. I think that there might be another slight leak else where as I keep hearing that "tststststtstsst" sound when accelerating and a small play from the RPMs at idle, but I'll give it another try next weekend.

My last question before considering the case closed would be: is there any special way of adjusting the wastegate or what I did is enough?

 

[b2]

10mm spanner to tighten the wastegate actuator bolt, then take it for a drive and check your boost gauge. You can then tighten or loosen as you need until you got it where you want, I had to badger around with it for a bit until I got it on the sweet spot. Caution will be extremely hot after a few runs so you may want to let it cool down a little in between runs.