Hi,

I've got the strangest 'malfunction' with my 1994 855 T5: the turbo boost pressure from one day to the next increased big time. Giving full throttle, I get the gauge out of scale whereas normally, it wouldn't exceed about 2/3d the scale.
At the point where the turbo boost gauge is past the end of its scale, the car starts making hickups.
Considering I didn't do an ECU upgrade, I'm left in the blue about what could be causing this.
Any ideas? Thanks in advance!

 

sounds like you've got something sticking. the hiccup mite be your fuel being cutoff at 15.5lbs of boost.

could you be more descriptive about what happend? do you have any performance modifications? does the car feel like it has more power or less?

youve probally knocked a line loose from your turbo. look at it and see if it has any open holes where a hose would go. there is a line, that when disconnected, that can cause a full boost all the time.

 

Hi mtneyman,

thanks for your quick reply.
I did not make any technical modifications to the car, I've always just tried to keep it in original and good state.
Last weekend though, a mechanic replaced a leaky cooling system hose that leads to the heater. That hose would be near the turbo charger I would guess.
About power: I would say it has more power, or at least picks up power at lower revs than it would do before.
I can't check the car right now, I'll do that later today.

What's the risk of this line you mentioned being disconnected?

 

Wastegate isn't opening up and it's just causing you to build boost. You're hitting fuel cut. check all vac lines going to turbo and make sure they're connected in order to the BCS. Search and you should find some vac diagrams.

 

Vacuum diagram should be printed on top of the throttle cable cover. gilber is correct - the wastegate isn't opening up. You either had the hose come disconnected at the turbo or possibly your tcv is bad.

 

Vacuum diagram is on my hood...fyi. I vote wastegate or vacuum to.

 

thatks for posting that, boxpin....its a LOT clearer than mine is.

 

So I have a question, because mine has been doing the same thing since I replaced my knock sensors/PCV system. The vacuum line going to the TCV, do they need to be connected in a certain order? Or can you hook them up any way? I didnt really pay attention to which line went to which spot of the 3 wires that connect to the TCV.

Wow as I read what I just typed I really feel like a dummy for not paying attention to that.

 

Uh, yeah, it matters.

 

Absolutely it matters. that valve is electronically controlled and directs air through each line individually when it should if they're in the wrong place, it's going to cause either excess boost or NO boost.

 

Uh... Thanks

Thank you for the explanation.

 

Hi guys,
Thanks for all the advice. Turned out there was a hose loose (duh), the top hose is torn off. My mechanic apparently was in a hurry when replacing the cooling water hose; I think I need to talk to him.


Cheap way of some extra power tuning by the way, maybe I should make it auto-unpluggable using a valve.

 

Fail. No. Do not do that, that's a dumb way to make extra power and a good way to overboost, potentially harming your engine. Get a MBC and boost gauge if you want more boost.

 

Yes, And it will hit fuel cut off all the time and the performance will stink because of it. MBC set just below fuel cutoff works great in mine. Got to smoke a late 328i with it the other day.