Usmc1488

Evening everyone. Ive got a 89 930 that im trying to short. The previous owner added a 1.2 bar spring and added an adjustable boost control that doesnt work. The overboost kicks in as it should and the car isnt fun at all. Ive disconected the inoperable dial a boost and now boost is slim to none. Does anyone have a diagram or explanation on where the two vacum hoses from the wastegate are supoosed to go? I have the workshop manaul and it doesnt indicate the routing of the vacum hoses.

Ps.
1.0 spring on order!

Mark Houghton

The top fitting on the WG bell housing vents to atmosphere. The stock factory setup has a metal line that attaches to the top of the WG and works it's way up through the engine bay tin. Doesn't really matter where it goes, other than open to atmosphere.

The bottom port connects to a hose that in turn connects to your intercooler, thus providing the boost signal the WG needs to operate.

I presume your '89 is no different than my '87.

Usmc1488

Thanks Mark, that helps. The connection to the intercooler has been butchered too. There is t fitting with a line that ran to the dial for the boost control. Anyone have a picturenof their engine compartment of how the line from the wg connects to the intercooler? Im looking through the workshop manual now. Maybe itll have a diagram.

RobT 394

Here are a few pictures from a stock 89. Hopefully it helps. First one is the WG but you cannot see much. Second is a picture of the vacuum line running through the engine tray and up the side of the engine. The vacuum line connects to the WG just above the engine tray. Third shot is the vacuum line connecting to the IC exactly as Mark describes.

Peter Carroll/Toronto

Some brands of waste gates have the fittings reversed. But the Porsche and Tial ones have the vent on the top. So the base fitting goes to the intake after the turbo. It depends on the design.

It doesn't make sense that it's a 1.2 bar spring and an adjustable controller. The controller adjusts from spring pressure higher. If you want an adjustable controller, you want more like a 0.5 bar spring. Or run with just a 1 bar spring and no controller.

Usmc1488

Pete i think you nailed it now seeing just .5 bar with the controler removed. When the controler was instaled the least amount of boost that was maintained was 1.2, trigering the overboost to kick in at 4500 and 1.2 bar. Going to reroute the tube to the ic, hopefully it fixes the issues. But i think a 1.0 spring is needed.

Mark Houghton

Yepper, you got it! Or a .8 bar if you want to keep things stock-ish. 1.2 is a lot of boost...addictive...will make .8 (or even 1.0) seem sluggish. Personally, I've never run over 1 bar.

Peter Carroll/Toronto

The fact that you got 1.2 bar on a 0.5 bar spring might just mean you are misunderstanding how the controller works.

There are two ways to plumb them. One is a controlled leak of the boost line to atmosphere. The other is a controlled bleed from the boost line to the vent on the wasegate. Both work.

With the controller valve closed, you should get spring level boost. It could be you are turning the controller the wrong direction. There are clockwise and counter clockwise version and you can't tell which it is by looking at it. Disconnect the hose from the Turbo end and try blowing through it to find which way is "closed". If it's closed you won't be able to blow.

You probably have it full open and the 1.2 bar is where the overboost switch cuts in...

Though a 1 bar spring and no controller is easier and always accurate...

See here:

Usmc1488

pete this helps aaaalot! Thank you. I have no clue how the adjustable boost is supposed to work.

Usmc1488

Ps just guessing what the spring might be.

Peter Carroll/Toronto

If you close the valve completely - or just plug that branch, you will be running on the spring. So that boost level is what the spring is.

somoney311

Alright gents this is great information. I am the owner of the car and yesterday we replaced the wastegate with a TiAL and the boost spring is 0.8. We re routed the lines so that the boost controller is now gone. The line goes from the intercooler direct to the wastegate and is attached to the side. The top does not have any lines to it so all boost control is from the wastegate. We are still having the same problem. I noticed that the boost control that is on the back side of my intercooler is not connected to any thing. I was peeking around the engine and did not see any additional wires that would go to it so I think the previous owner removed the wire to bypass that system. (please back me up on that thought.)

So my concern is that the overboost is not the issue. I am not sure what else could be causing the sudden "engine cut off". it seems to me that if I give the car 50% throttle then I am fine. I can get boost (not sure if it is full boost or not) and make it to the redline. But, if I add throttle then at some point the engine cuts to idle (regardless of RPM) and I have to release the throttle and go to neutral to "reset" the engine before it will let me accelerate (to any degree) again.

James

Peter Carroll/Toronto

If your original boost cut-off switch was disconnected it could be because it was replaced with another one somewhere else. So look for another sensor.

Cutting out could also be due to a fuel mixture which is uncombustable too.

Sounds like time to visit a 930 specialist mechanic...

BTW, I came across my original documentation for the Tial Wastegate and it has a nice diagram. Posted here as a reference...

somoney311

Peter,

I am on the same thought. Time to let the people who know what they are doing to look at the car. BTW I also replaced the rotor and the distributor cap. Once again to no avail. I was thinking an air/fuel mixture may be an issue. The car runs really rich so you may bo on to something. I am not sure how to play with that and I will leave that to the pros.

Thanks for all the help. This is a great community with great resources.

James

pdqcarrera

No doubt tuned rich to allow 1+ bar boost without melt down. Unfortunately stock CIS on high boost compromise required (especially without dyno tuning).