Searched and didn't find anything so I hope this isn't a silly question.

Have a 07 MCS and have been running the AccessPort since December on the stage one non FMIC 92 Octane tune. No problems and love it.

On the way home today I got on it a bit in second, and thought I heard more "BOV" noise than normal, next gear and no power. Car is in limp mode and only seeing 1-3lbs boost.

Check the trouble codes and see
P28b1
Bypass Valve Signal

Clear the code and it returns as soon as I start the car.

Any thoughts on causes, where to look, how to fix?

This is my first turbo car but consider my self capable of simple repairs.

Thanks in advance!

Chris

 

Some more symptoms to maybe help with diagnosis. Had a chance to drive some more after reseting the code. Check engine light stays off but boost is inconsistent. Acts fine for a while then only see 1-3 lbs boost for a couple min.
Seemed to "fix itself" and I had boost again if I revved it up a bit in neutral and then got back on it I would see normal boost again.

Same code is still showing on Access Port but no check engine light yet.

Nothing seems to be loose and no strange noises...

Have an appointment to get it looked at on Monday but would be nice to be able to sort it out myself.

 

I blew the plastic coupler of the boost tube going into the throttle body once, it was before I had any code reader so I'm not sure what the code was, but it gave me a CEL. Everything was still under warranty so I just brought it in. If it was something like that, in neutral if the tube was holding together it might build up a little boost, but when you drive if the tube comes undone there goes your boost.
It may not be something like that, but hopefully it will be an easy fix!

 

Thanks for the input! Ive poked around and cant find anything obvious loose or broken, I am taking it to Mach V tomorrow and hope they can sort it out. If it ends up being the bypass valve I am probably going to just replace it with the Forge unit from Way since I have plans for plenty of power mods this summer.

 

Quick update incase anybody else runs into this. Went to Mach V in Sterling VA and they were able to sort it out. Gotta say if you are in the DC Metro or NoVA area be sure to check them out. They took their time and tested everything out and fixed it up for a very reasonable price.
Sounds obvious now from the code but I needed a new Bypass Valve, it was sticking open and also seemed to be slow to open.
Boost comes on much quicker with the new valve and does not overrun the target boost with a big spike before settling in. Engine seems to run a bit smoother as well.

 

Hey all,

was wondering if anyone has run into this problem. I have a 07 mcs with the following mods since 2008 full milltek exhaust, JCW air filter, forge intercooler and forge resonator delete hose. Back at 2011 i had a custom tune and it worked wonders. The car back in November started to burn a lot of oil so i decided to have the motor opened up and replace cluth and all the piston rings (they were in terrible shape)and all the necessary things on the cylinder head. i did not have any carbon build up. Since then the car has the issue of dropping boost and throwing this cel. I tried 5 new DV valves, all the tubing and things that had to do with the vaccum replaced along with the BCV. new intake manifold and sealings. Even the vaccum pump and the vaccum canister! Tried 4 different used turbos as well but nothing changed. Car runs perfectly under no boost. All electrical lines were checked as well. The weird thing is that some days the boost is building and holding well and after lets say 30 minutes of driving it will start dropping or no building at all. Or usually after the first heavy load at 3rd or 4rth gear it will start doing it immediately. I dont get a half power engine light only the P28b1 code stored when we connect the diagnostic. Compression of cylinders are ok , new spark pugs, new HPFP, smoke tests do not show any boost leak, new cylinder head cover as well.

3 months now we cannot figure out what the hell is going on and it drops boost and gets this code! A brand new turbo is on its way at the moment and another ECU unit is on its way as well but i doubt this will be the solution. Any ideas what it might cuase that shitty trouble?