Peter Seillwell

Gents- my 1989 930 loses all power and boost when full boost is reached on the boost guage no matter what rpm. It goes to full boost then "shudders" and loses power, but will pull boost if modulated with throttle to keep it below the maximum. The car is/was otherwise super healthy with no problems and appx 60 K miles. What is the likely diagnosis for the malady? If the waste gate is at issue should I get a "eurospec" stiffer spring? Is it hard to change the spring- I am mechanically capable but have never worked on the turbo apparatus. thanks for your help, sincerely, Peter

fullquack

Without knowing how your car is configured, this is only a guess, but it sounds like you are simply hitting the "over boost" threshold, and your factory over boost switch is kicking in & cutting off your fuel supply.

Your factory waste gate should be opening up at around .8 bar boost, if everything is still all stock, so if you can get 1 bar of boost, something has been altered to allow this higher level???

Mark

Mark Houghton

If you're at 1.0 bar (or possibly above that, pegging the gauge) then as Mark has suggested it's your overboost protection circuit kicking in to save your ***. If you're only getting to .8 bar and still she's shutting down as though over-boosted, then there would be an issue with your overboost pressure switch tripping too soon.

A stiffer spring is not what you want to do with the WG...it would allow you to boost even higher. If you're truely overboosting, then check to see that your pressure signal hose is connnected to the WG and to the intercooler. Another possibility that could result in overboost would be a torn diaphram within the WG itself.

schnele

The Marks have it on the mark, your car may be seeing higher manifold pressure because of the cool dense air that these cars love. You may also want to do a search on over boosting, as this issue has been discussed in detail here. Good luck and welcome, by the by a proper introduction requires a photo of the car.

chiplynch

Hey guys, I had this same problem ono my '81. This is what it turned out to be. On the stock 930 manifold, or the section in between the intake manifold and the intercooler, there is a built in overboost or bypass valve. There are plastic seals on either end of the bypass valve and a long spring and a piston
in the valve itself. When I pulled my intercooler off and the mid section of the manifled beneath the intercooler to install a Fabspped longneck intercooler, I examined the parts that came off. The only moving parts were this bypass valve. So I undid the screws and look at it. The plastic selas had decayed to a point where they were just debris..junk..JUst to check my conclusion, I ordered the two $4.00 seals (part # 930-110-149-00M17) and rebuilt the valve housing and placed it back on the car. Problem solved. If you can tune up a 930, you can rebuild this valve housing..."nuttin to it"

best wishes from New Orleans!! GO LSU beat BAMA!

Mark Houghton

Yes, those seals if really bad and leaking could cause a serious boost leak resulting in boost loss and extremely rich running conditions/loss of power. But, that valve has nothing to do with overboost control and simply is a bypass valve that operates when you take your foot off the gas....the resulting vacuum pulling the piston open to re-direct the boost air back to the front of the turbo to keep your turbo from stalling when lifting off the throttle. On a well running engine, you could disconnect the vacuum line going to the valve and have no impact on how much boost is created but may see more turbo lag between shifts.

What Peter has described is high boost, perhaps uncontrolled, which usually points to the wastegate whose function is to control boost....resulting in the overboost protection circuits kicking in and shutting down the fuel pumps.

Peter Seillwell

Thanks Guys, I will check the overboost switch and circuit. Also will post a picture of the car soon. sincerely, Peter