So I just replaced the turbo's on my car and got the motor in and piggy the Dp's. After getting it together to it out for a drive open DP and was pulling good and making 15psi. Took it up to my buddies shop and we finished welding up the pipes cause I eliminated the rear cats and flex joints. After we finished the exhaust up last night we took it ok for a cruise and WOT in any gear im only hitting 5 psi. This car has a GIAC B box tip trans Ko3 turbo's all maintenance was done by vast and also has a Vast MBC. I drove it to work this morning and threw a CEL probably from rear O2 don't have the non fouler on yet. I need to order a flashloader cause the PO didn't have one. I have no clue why im only hitting 5psi when it was hitting 15 before we welded up the exhaust. What should it be hitting with the GIAC? I bought the car with a bad turbo and the PO said it was hitting 20 with spikes around 25 before the turbo went bad. Any help to send me in the wright direction is appreciated. I searched around a bit and can't find anything that related to the problem I am having.

 

Ok took it to my buddies shop and got these codes. P1476 p1136 p1138 p0741 also looked the the freeze frame data and coolant temp is showing -18f when ut threw the evap code and showed -25 when it threw the lean codes. My coolant demo sensor in the rear has been upgraded to the green top. Does this car have more than one coolant temp sensor? I think I seen a coolant temp sensor in the front lower coolant hose. Talked to the po and he said the car is going into soft limp mode. When the car is started and let it warm up if you get on it it will pull hard and hit 15psi but after about a minute or 2 it will go back to 5psi and stay that way till you turn or the car and let it sit for a few. Then when I restart it and take off it boost to 15 again. We found a vacuum leak at the gromet in the fire wall. Getting a new gromet today hopefully. Any help to fix would be nice. I don't want to just throw parts at the car that wont fix it. Hoping the coolant sensor and vacuum leak will fix my problem but would like some input. Thanks

 

there is a coolant sensor in the lower radiator hose. A severe vac leak can put your car into limp mode. I'd replace as much vac line as possible, if its old. Is the MAF clean?

 

I found my Vac leak yesterday there was one hose I didn't see when I put the car back together. Still only making 5psi it will make 15 for a second when I first go to drive it but as soon as it does it drops to 5. Is there something that might be causing this. It has a Bosch Maf and im going to see if I can get a Hitachi but it is clean. Is it possible the oil from when the turbo blew killed the O2 or Egt. Just the way it acts it seems like it is a sensor. Im going to smoke test it later but all Vacuum lines are it good shape. Is there anyway to test the O2 or EGT to see if they are working.g.

 

Ok I found my problem and it was the MAF causing my boost issues. I also have a 2001 A4 1.8t and swapped the Maf today and took it out. Im boosting good but only hitting 13psi and the po said it should hit 18 to 20 so I am going to smoke test it and see if I have a vacuum leak. If no vacuum leaks I am going to boost leak test and see what I come up with. Can someone running a s4 with a GIAC b box with piggies please tell me what psi you are getting and what vacuum hg are you getting at idol in park?