A3 1.8t Logs 150hp

Long story short I have been battling overbosting problems where car would jerk and cut at between 3-4k.
I dont know if the car has been mapped somewhere previously but looking at the logs I would say it has.
My first suspect was faulty N75, I have checked the voltage at the wires and i can see 12-13v.
When testing N75 outside on the bench it works, but it appears that in the car it just fails and is stuck open. I have done 2 logs and from what I can see is that my N75 appears to be dead when it needs to pulse to achieve desired boost, cars is lacking fuel across the rev range and looks like my wastegate is not holding 7 psi pressure.

Also, took out injectors and FPR and confirmed they are in good condition.

When I got the car I have done all the pcv check and delete, simplified the pcv system. I dont have any errors. but when I completed logs and checked for errors I was greeted with system to rich message. I think this could be because previous owner took the cat out and second O2 sensor is messing with the system.

What would be the next step? Replace N75, what about fuel? Pump maybe?

Cant find where the attachment button is for docs. Here is the google doc link.

https://drive.google.com/open?id=0BzgdK6BxpnTBZm9fbGF3aEdGRzA

Hey Bill, thanks for replying.

Here is what I have observed when driving he car and logging. I have logged the car with with only pressure connected directly to the wastegate and could see only 0.3 boost. When logging car like this I forgot to disconnect my N75 and when I checked logs I could see duty was up and down from 0% to 95%. This was logged on wastegate pressure and electrically connected N75 -https://drive.google.com/file/d/0BzgdK6BxpnTBRUdIbEdNTVlTUzg/view?usp=sharing

When you mention the throttle pedal you got me thinking - when I observed throttle percentage against the plate angle I could see taht when I press the pedal not all the way down maybe half the way my throttle plate angle would jump to 100%. Here I was able to track in logs -


is this normal behavior? Could it be dodgy pedal as when I had boost spikes and jerking it was between 3 - k rpms.


On the other hand, is there any kind of restrictor in the nipple pointed in the picture. When I was flushing the system i had hard time taking air out. I could see that coolant from return line doesnt flow into bottle when connected to the nipple or maybe it does but in a very slow rate. When I took down the pipe I could see the coolant flow ok and when increasing rpms coolant flow increases. When I tried to blow or suck air through this plastic nipple I could not. Is this designed like this or this is blocked?



thanks for all help.

Best,
Dragan

badger5 said:

whats going on here>? much timing pull...

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That is what bothers me a lot. I have tested car with 4 different MAFs all genuine, 2 new, one from friend and my MAF is 1 month old. Same thing. Changed all 4 coil packs. Bought red tops one r8, same thing. New spark plugs BKR7E less than 500km on them. Same thing. DV is new, tested and it doesnt leak, hold the vacuum when top pipe is closed. PCV delete has been done. I am currently venting to atmo but think that shouldn't cause this timing pull. What else could I look? Massive boost leak somewhere? Can second O2 sensor cause this. My second O2 is working, but previous owner took the cat out and I think that readings are a bit low. Might buy cheating bung or disable through the eskon.

desertstorm said:

Sorry can't help the OP with your issue, but what software are you using to log the data?

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Yes, as Bill said me7Logger from nefmoto.

Bill, I was able to narrow down the problem a bit. Massive boost leak was at the dump valve. What is confusing me is that dump valve is brand new, genuine. I have tested it and it doesn't leak. I have pushed the rod and closed air from accessing small nipple and rod is holding in the position and it doesn't go down. When trying to blow or suck air through the nipple it doesn't allow me. Also, when trying to blow from both sides that has positive boost and the one that goes into the turbo inlet same thing, hold the rod closed. Orientation is good and nipple is on top when installed in the car.

I have tested car without DV and car is working way better and is holding boost and doesn't splutters like before. I am not driving it like this i wanted just to test it.

What could cause DV to leak boost when obviously it is in good condition. My vacuum is connected to one small nipple under inlet directly to DV.

I have another small leak somewhere that I have to action, but this is something I don't understand. My vacuum readings are per spec looking at the gauge and VCDS.

Any help would be grateful. Here is the image how it is connected.

When I take of the small hose from the DV nipple i can hear vacuum pulling. It is not blocked or anything. I think DV rod is sticking and not closing completely as last night car was boosting fine wasnt spluttering at all. After some time, all of the sudden car wouldnt boost past 0.3 bars.

I will have to replace DV and test it. Will report back when I get another one.