Boost Problem

[kezcapt]

Hello All. I have a 2005 Turbo S with Bailey Dv's and stock DME. I noticed at some point that I was only making .4-.5 bar of boost. I checked with my Durametric and there were no codes. In fact, the car runs beautifully. I completed a 30,000 mile service two months ago and the car was running like a champ.

I researched some posts and came up with a list of possible problems. The first thing I did was look for boost leaks with a leak test system. I pressurized to 1 Bar from the turbine inlet and the system was tight as a drum. I next tried to see if I could reset a possible limp mode by disconnecting the battery but no joy with that either. Lastly, I disconnected the MAF and tried to see if that was the problem but that did not restore boost either. I also ran the car with the durametric looking at boost and MAF values and the instrument cluster is giving correct readings. I am running out of Ideas! The only things I can think of are the DV's or the N75 controller. BTW I manipulated the wastegate levers and kept them in the loop for the pressure test. Any ideas would be greatly appreciated.

Cheers, Rob

[Loren]

The most common problems of loss of boost are air leaks.

Check the hoses (under load) and check the DV's.

[kezcapt]

Thanks Loren, I pressurized the system and checked with soapy water but there were no leaks. Can you recommend a preferred method to test the DV's?

[kezcapt]

Problem solved: It turned out that the change over valve (aka N75) was faulty. It was failing, pressurizing (pushing) the waste gate open and thus allowing only .4 bar boost. (the spring pressure default). I know the most common reason for the boost problem is a boost leak (or DV) but, like I said in my original intro, the system was tested and was tight as a drum. Thanks to Loren for trying to help. The interesting take away is that the N75 can malfunction without throwing a code. In my case the valve was not "dead as a doornail" but it was close.

If you want a good diag tool for your tool box then get (2) 3.5" rubber couplings and (2) 3" pvc caps to make yourself a pressure test kit.. Connect at the turbine inlet with a few basic connections (i.e. air hose quick connect) and a gauge if you want. The main feature should be a pressure regulator on the air compressor (set to 10-14 psi). Some posts advise to pressurize the intake manifold inlet rather than the turbine inlet. This is pointless from a number of perspectives but the main objection is that it does not re-create the actual operating condition which is to pressurize the induction side of the system. You could say it will test the Dv's but there are more efficient ways to do this. Pressurizing the system is not rocket science folks. Lastly, some posts say that you should pressurize to 1.8 bars (25psi). This is also pointless unless you are running some kind of race setup. Again, the objective is to re-create real world conditions. For most of us that means .8 to 1 Bar. There is even a youtube video if you need a video example. In summary, pressurizing the system is cheap and easy to do. Just don't make more problems for yourself by deviating from the basic objective of re-creating the basic operating conditions. I hope this helps.

[Loren]

Glad you got it sorted!

:thumbup: