Hello everyone. I am new here obviously but here is the nightmare I am having. I am working on a 2001 Audi A4 for a friend. It has no power at all. This thing will not spin or even slip a tire on gravel. So it does not have any boost. Checked the boost by taking the hose off of the intake of the motor and it was very weak. Looked at the turbo and it was cracked. Ordered a replacement turbo and installed it. No change. The old turbo by the way had a leaking bypass valve. Ok so next thing in line we changed the N75 valve. Still no change. You can not hear the turbo at all and there is no boost. So I did a smoke test on the boost system from the turbo to the intake of the engine all was good. Checked the DV all was good. The only code I get from this thing is P1556. Did a smoke test on the vacuum system all was good. The car runs great and the only issue is that it is a pig. Like a school bus full of nun's would pass this thing by. Any suggestions would be very much appreciated. oh by the way the cat does not seem to be clogged.

 

Welcome to AF!

Only slightly less than normal for a stock B5 turbo. The turbo was put there to make the small displacement 4 cyl. driveable and efficient, not for big horsepower.

Not a good assumption.

You won't be able to build boost like this, there has to be a load on the motor. With the car parked and the throttle body hose disconnected all you're doing is wasting gas.

Where? Pics?

What was your test procedure for this?

P1556 is charge pressure control: negative deviation. This, along with your other symptoms points to a boost/vacuum leak or some other problem with the intake, turbo, and associated plumbing and hardware. You need to tap the vac line between the intake manifold and FPR and connect it to a boost gauge, even if only temporarily. Stock boost should be around 9psi or so. How's the maintenance history on the car? Original fuel filter? How do the plugs look? Are you sure there were no other codes?

 

first off, how could you check the boost pressure by taking off the hose? not only would this mess the car up since youd create a boost leak, but unless you were hanging on for dear life while the car was moving, the car wont boost while in nuetral. it needs to be under load. and that p1556 code is kind of a big deal. did you look it up? it is a code for REDUCED POWER. did you hook the n75 back up properly? the n75 is one way of limiting power while you are in limp mode

 

damn, beat to it by cca4 yet again. wheres your tech guru status? id also like your phone number so next time i have problems with my car i can call you up

 

They were gonna make me a tech guru but I post too many memes and sarcastic animated gifs as responses to stupid questions LOL

 

ok all sarcastic comments aside I removed the vacuum line from the DV valve and from the waste gate and then pulled the hose from the throttle body to see if the turbo was even spinning. It was so that is why I did this. I tested the DV by taking it off of the intake hose and trying to blow through it. Then I did the same while putting a vacuum pump on it. It was working properly. I tested the entire intake system with a smoke machine and there are no leaks. Yes I installed the N75 correctly the long tube in the intake hose, Bottom tube to the turbo and the remaining tube to the wastegate.

 

also I checked all systems with my snapon verus and there was no other codes.

 

Wasn't trying to be a smart ***, just had to ask those questions. So we can rule out a blown turbo (new), a bad DV (good test btw), bad N75 (new). Sounds like your N75 is plumbed properly and I assume it's plugged in. I would also check your n249 (under the IM) and your MAP sensor (on the intercooler). Make sure they're plugged in and don't look fucked up.

Do you get a recurring CEL? Does it ever flash? Do you ever feel any bucking or misfires at WOT?

 

just because your n75 works doesnt mean its not what it limiting your power. i believe wastegate pressure on a k03 is like 3 or 4 psi. if you had a boost guage it would help quite a bit. but yeah, id check the n249 as well, or completely delete it on run the dv vacuum line straight to the manifold. if you have your proper radio codes i would unhook the battery for a few minutes to reset the ecu. rehook it and see if the power came back, and see which codes came back. and do you have the proper licsense for the snap on tool for euro cars or are you just using the global obd2 functions?

 

I actually used our launch scanner now that I think about it cause I didnt have the audi license for the snapon I am going to try to eliminate the N249 first. So all i have to do is block off the old vacuum line and hook a new on up to the intake? This will not cause any codes? There is no cel that is the weird part. Only the code. I will try to reset the ecu by unhooking the battery but I believe that I already did the same thing by resting it through the launch computer.