Can anyone help me with the location of the boost pressure switch on an '85 930 with CIS. I have fitted a 1.0Bar spring and now the overboost switch is working at .9bar, obviously stuffed. Any diagrams etc can be emailed to dewolf@iprimus.com.au. Thank You.
Scott

 

It' the white sender on the left. This is on a Kokeln I/C.

On a stock set up, it's located on back left of the pop off valve.

 

Thanks for that. Now what does that pop-off valve look like? LOL

 

Here's Nathan's and someone elses..

 

Those pics are from the rear when viewed in the engine compartment.


It is screwed into the recirc assy on the left hand side at the back. It has one wire running to it. The boost gauge sender is near it but has two wires connected to it, is much larger and has a red rubber boot around it.

 

You have several things to consider before you jump to the conclusion that the overboost switch is broken. First, do you have an independent boost gage? That little thing in the tach is for looks only. Second, is your wastegate the original? If it is it could be leaking badly around the stem and therefore causing the overboost switch to cutout. Third, you could have momentary spikes in boost due to a poor wastegate and the overboost switch will cut in for a breif second but enough to cut off the supply of fuel and make the car run like ****. Fourth, you could have a bad overboost switch but I would not bet on it. Start with a good boost gage to find out what is happening. Then you will know which way to proceed from there. I have a VDO boost gage in place of my clock and an adjustable boost control and I had to adjust my max boost to .98 to keep the overboost switch from activating. On hard acceleration with fast up shifts the boost would exceed the boost cutout switch momentarily and I had to adjust the boost back a small amount. Do not do what some of the track guys do and ground out the overboost switch! They generally have much stronger engines than stock and can handle a big spike occasionally but your stock engine could easily be ruined if you disconnect the switch.

 

Thanks heaps guy's, I really appreciate your help. As for the wastegate, I replaced the diaphram and before I did that ( 1.0 bar spring already in place ) it would not cutout, since replacing it, it does. It won't reach full boost in 1st before redline( can hear the tyres fighting for traction ), but will start pushing .8 bar by 3000rpm.