Hi all, this is my first post to the forms. That being said I have read through many in the last few months that I've had my 97 850. I've been trying to track down a really odd boost issue I've been having and I would reallyyyy love to have some boost.
OK so first of I'll start with the fact that this might be a bit confusing... I can build boost, but only with the yellow marked hose on the boost control solenoid off. I know this goes to my waste gate so I've done a bunch of all data research and digging through countless forums. I've checked all of my hoses and replaced allmost all of them except for the intercooler piping. The piping itself is a little soft but not bad. I checked all three sensors that contribute to the boost system, mass air flow, wheel speed sensor, and throttle position sensor and all three seem fine. Just today I re did my pcv system as well. I have no engine light on and everytime I think I find the problem it sends me back to square one. I have tried replacing the bcs as well with no luck. Some one PLEASE help me get my boost. I had a 95 850 turbo that drove AMAZING I'd love to have my t-5 drive at least close to what my 95 was.. Thank you in advance!!

 

It would make some sense to suspect that the boost controller is unable to really control, but that for some reason this doesn't set a check engine light. So for instance, let's say the solenoid is stuck. that's just an example of something that might make sense.

That is the sort of thing that you could figure out by doing a few experiments. vacuum is easy to measure, so you can set yourself up to monitor what is going on in those lines when you're driving.

 

Thanks for the reply, so basically setting up a vaccume gauge and watching it as I drive? I'm really new to working with turbocharged cars so my question is how would I do it and what would I be looking for. I've read on other fourms about doing this, only they all seemed to be a different scenario than mine. My boost gauge in the car reads just fine I think, cause with the waste gate hose off I build boost just fine. When I release my foot from the gas it opens the waste gate and releases so doesn't that pretty much tell me that the turbo and most everything is fine?? My thought was that it's something else possibly in another system that's telling the ecu to limit it's functions.. Also tried cleaning original bcs (not sure if that would've done anything or not) and replacing it with one I know works from my previous 850 turbo

 

There are some issues that cause the ECM to cut power, but I would think you'd get a check engine light for that. I guess we need an exhaustive list of issues were boost is deliberately cut.


Anyway if you check pressure in the yellow line, then that would tell you how much the boost controller is sending to the waste gate. If you check pressure on the yellow and red lines at the same time, then you would know whether the boost controller is "doing anything". I said vacuum above but it's really pressure. A compound vacuum gauge will read it.

 

Step 1, install a real boost gauge, even if it's a temp install.

Step 2, If you have any pending emissions codes, the ECU will dial your boost down to about 3 lbs.

Step 3, Soft boost pressure tubes can breath and cost you pressure.