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View Full Version : Boost problem with chipped 1.8t AEB



mathieums
08-05-2009, 07:32 PM
Hello guys,

I've got a weird problem with my car the other day while heading to montreal.

Since I bought the car 3 years ago, the car would always boost around 10-12 psi and peak around 14-16 psi.

But the other day the boost gauge indicated that I was peaking and keeping more than 20 psi on the stock k03 turbo.

So I took it easy because I didnt want to run lean. After a few kilometers I tried again to floor it and it was stock at 5 psi.

Right after, I try it again and then it was going nut. Jumping from 20 to 5, then to 10, back to 5 and right back to 20.

So I arrived at destination. I stop the car and do my things. After a few hours I try the car and it was back to normal.

Now everything is back to normal but it only boost between 8-10 psi and peak around 12.

What the hell is wrong?

DV? I don't think so.
N75? Very possible imo
Wastegate? Possible...


Anyone have an idea?

Thanks
Mat

nyca4tqm
08-05-2009, 07:45 PM
boost leak

2Rude
08-05-2009, 08:48 PM
kinda what i'm experiencing, do you have loss of power/acceleration?

walky_talky20
08-05-2009, 09:18 PM
My vote is for bad N75. My friends S4 was intermittently making more boost on an APR chip than it was supposed to. Then when he got bigger turbos and a custom tune, the tuner was having trouble turning the boost down. It was spiking way too high and even invoking fuel cut. After fighting with it a bit, he changed the N75 and immediately a huge difference. The boost was no longer spiking wildly. It seems they respond worse as they age and the symptoms are worse yet when you run higher boost levels. I saved his old one and thought I'd try it on my A4 to get a bit more of a boost spike. Worn out N75 upgrade FTW!

I don't see how a boost leak would cause a boost spike/more boost. Unless, perhaps, the boost leak is in the line between the N75 and wastegate actuator? I suppose the failure could also be in the wastegate actuator itself - like sticking or a leaking diaphragm.

terraflata
08-06-2009, 02:08 PM
I would say the N75. I would also say its not worth getting a replacement N75 but rather something more robust in design (i.e. Forge). Could be the wastegate acuator not opening, or functioning correctly. The fact that you shut off your car and it stopped doing it but now doesn't boost over 12 psi is slightly perplexing.

Boost leak test, then DV. It's a process of elminiation.

terraflata
08-06-2009, 02:10 PM
BTW. If you are in Montreal I could most likely give you the DV off of my car seeing as I am soo far from needing it, and it will never be going back in my car anyways.

mathieums
08-06-2009, 07:00 PM
BTW. If you are in Montreal I could most likely give you the DV off of my car seeing as I am soo far from needing it, and it will never be going back in my car anyways.

I have a Forged diverter valve. I don't think its causing any problems. I put new grease in it last year.

-----

Where could I buy a forged frequency valve? I looked on ECS and 034 and I didnt find any...

Would a ECS "race" frequency valve do the job?


Since it peaked over 20 psi of boost, maybe it blown off a hose joint or something which made a leak. That would explain why I don't boost as much as before.

terraflata
08-06-2009, 08:16 PM
Spiking over 20 PSI isn't something that should blow off a hose. But of course, checking for leaks/disconnected hoses isn't a bad idea.

I have been trying to search, but cannot find anything that says at what pressure the K03's wastegate is supposed to open, but obviously if it is 20PSI or under, and you saw it spike above 20, then the wastegate could definately be your problem. I know Mike Hood had boosted a K03 to 26 PSI for quite a while without scrapping his turbo. He would probably know the specifics about the wastegate. Might be worth checking into.

Terraflata

walky_talky20
08-06-2009, 08:32 PM
I believe it needs around 3 psi to open. My brother's car has the APR chip with a valet program which is supposed to limit the boost to the minimum (open wastegate as soon as possible) It spikes to 3 psi and holds at ~0.

terraflata
08-06-2009, 08:47 PM
A valet setting will not affect the wastegate in any way. The wastegate is not controlled electronically. It's limits the boost by changing tune (sort of like being able to switch from stock tune to APR tune). If you have a problem with your wastegate it is a mechanical failure of some sort. This is why external wastegates come with several springs with different settings to control different levels of boost.

Terraflata

walky_talky20
08-06-2009, 09:01 PM
A valet setting will not affect the wastegate in any way. The wastegate is not controlled electronically.

Yes, the APR valet setting opens the wastegate earlier. This is how it limits the boost.

The wastegate is controlled electronically through the N75 wastegate frequency valve. The computer controls the wategate actuator via electronic signals to this valve. This is how the ECU is able to hit a target or "requested boost".

If the boost pressure is erratic and the computer is unable to control it properly, it could be failure of the frequency valve, the wastegate actuator, or the related wiring and vacuum hoses in the boost control system.

terraflata
08-06-2009, 09:31 PM
Yes, the APR valet setting opens the wastegate earlier. This is how it limits the boost.

The wastegate is controlled electronically through the N75 wastegate frequency valve. The computer controls the wategate actuator via electronic signals to this valve. This is how the ECU is able to hit a target or "requested boost".

If the boost pressure is erratic and the computer is unable to control it properly, it could be failure of the frequency valve, the wastegate actuator, or the related wiring and vacuum hoses in the boost control system.

I have no idea how it is supposed to open the flapper earlier. The flapper for the wastegate has a spring on it, set for a pre-determined load. On some turbos there are threaded actuator rods that can adjust boost, but these must be adjusted manually. External wastegates have to be adjusted by changing springs. I may be completely wrong, but I am sure I am not. In fact there isn't even a single wire connected to the turbo, so I don't see how it could receive a signal. And in fact when you receive these chips, it's usually because you sent your ecu away to get chipped. The only thing that you install back into your car is your ecu. Also the N75 isn't a wastegate, it does not regulate turbo pressure, it simply diverts returning air pressure to your air intake (while a BOV vents it into the atmosphere) to prevent compressor surge and damage to your turbo.

Someone can correct me if I am wrong.

Terraflata

walky_talky20
08-06-2009, 09:59 PM
Diverter valve:

http://www.ecstuning.com/product_library/225/300/Diverter%20Valve,%20225hp%20Audi%20TT%20Version-Priced%20Each.jpg

N75 Wastegate Bypass Regulator Valve (Wastegate Frequency valve):

http://www.shop.thedubnutz.com/images/1202865210350-1326903790.jpeg

N75 operation explained here:
http://s2central.net/ds_N75.html
http://forums.audiworld.com/showthread.php?t=1476692

terraflata
08-06-2009, 10:15 PM
OWNED! LOL. I don't know why, but I kept reading N75 and thinking diverter valve. Thanks for bringing me to school. With that said it sounds exactly as you said. Failing N75 or related wiring or vacuum hoses. Of course everythings best bet right now I suppose.

Terraflata

walky_talky20
08-06-2009, 10:24 PM
Haha, no problem. Happens to me a lot, especially when making posts way too late at night. Reading electrical wiring diagrams is especially difficult at 2AM, lol.

Jc61990
08-06-2009, 11:53 PM
did u check the wastegate arm to see if it was broken? ive heard of broken wastegates giving you really high boost issues.

mathieums
08-14-2009, 08:04 PM
New DV
New N75
New pressure regulating valve

Problem solved


How much pressure can take the stock 710N DV?