Background: 99.5 1.8T Quattro Tiptronic "Sport package" with APR Stage 1 chip installed at 108k miles. I bought the car with 107k miles. Other than that, all I've done has been correct a leak on the fuel-evap system and a coolant leak from the water temp sensor.

Car seems "sluggish" to me, so I ran some logs on VAG-COM.

Can't log Block 115 on this one, but the max value I get for MAF is about 130 g/s.
N75 valve (stock) duty cycle when I go full throttle, goes from 0 to 99.6 and stays at 99.6 all the way to redline, etc. until I lift.

Lambda % goes to 0 when revs go above about 2.5k to 3k rpms all the way to redline when at full throttle. Otherwise it stays inside a +5 to -3 range when I am not at full throttle.

My first guess is that there is a boost leak. I haven't started looking at anything yet, but I bought a new DV because everywhere on this site, I read that if you chip the car, you'll need a new DV since the stock one one hold the higher boost, plus they wear out and my guess is that this one is the one that the car came with from the factory.

Would a boost leak explain what I see as low MAF numbers?

Idle MAF values are 8.4 with the car in gear and about 5.4 with the car idling in neutral. I guess I'm trying to get an idea of if the MAF might also be bad or not. I'm thinking it's OK, since Lambda is not showing the car running lean, but I'm not sure how the MAF reading correlates to boost, except to assume that the higher the boost, the more air is flowing through the MAF.

The other thing is that on full throttle, the Throttle Angle % reported is 86.4% I've run the throttle adaptation a few times, but no change. I don't know if that is normal. The car is DBW.

Comments, suggestions?

Oh, since this is my first post here, I'll throw in a few newbie keywords like BOV, S4 engine transplants, MBC and ABS light, for good measure.

Thanks.
Ony

 

you probably have a leak in that area... or you pulled hard on the hoses to fit it in and they popped off. Definatly would suggest started to look there.

 

as IWas said, check all hoses

 

Swapped the DV tonight. The old one was completely busted. The car definitely feels stronger, but the logs still show the N75 duty cycle going from 0% to 99.6% and staying there until I lift. That makes me think that I'm making more boost, but still not hitting the target max boost, so there's probably still a leak somewhere.

I ordered a boost gauge so that I can have a better idea of where things are and from there, I guess I'll keep hunting for leaks. I'm not that familiar with Audis, but my guess is that most likely the problem is in one of the vac. lines, maybe the one that connects to the intake manifold by the front of the car.

What boost level should I expect out of the APR chip? It's a 91 octane "Stage 1" program in an otherwise stock car.

 

15-17

 

Cool.

Bought an APR boost gauge kit, but it's missing the "T", so they are sending me one. I searched a few local stores last night for one, but could not find one.

I looked for any broken hoses and did not notice anything. Looked at the 90 degree hoses, etc. and they all "seem" fine. A lot of the hoses look like new. You can read the white lettering with the part numbers on them, etc. Once I have the gauge installed, I'll have a better idea and from there, I guess I'll be making a pressure tester, if the gauge shows me that there is indeed a leak. My only current indication that there might still be a leak is that the N75 Duty Cycle stays pegged at 99.6% when under full throttle, all the way to redline.

Is the N75 valve known for going bad, like the DV, or do people swap them to increase boost/improve spoolup?

 

Installed the gauge. I get 5psi in first and about 6-7psi in second and up (tiptronic, not manual). When the car is shifting, boost spikes to about 10psi (remember, no lifting during a shift on the auto) and quickly drops back down.

If I disconnect the line from the N75 to the wastegate, I still get the same boost levels. I jiggled the wastegate actuator and it doesn't move, past a tiny bit of freeplay, which I assume is normal. I tried installing the DV backwards, checked all vac lines, etc. and can't find anything broken.

I made a pressure tester and connected it to the solid pipe under the radiator. I found a leak on the "Y" shaped pipe, the Secondary Jet Pump.

The interesting thing is that when I applied pressure with the tester, I can build pressure all the way up to 15psi or more (my tester has a gauge on it) and then see the pressure go down to 0 in a few seconds, like maybe 10 seconds.

Could this leak be enough to keep my car from boosting any higher than 6 or 7 psi? It took us a while to find the leak, we could hear it hissing, but it wasn't like the thing was completely apart. I'm just not experienced enought with searching for boost leaks and Audis. I've had turbocharged cars before, but fortunately never had a boost leak until this car.

 

According to German Car Repair in Roswell, GA, the turbo is toast and that is why it won't boost beyond 5psi.

New turbo being installed right now...