Thread: 930 Cutting out
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mark houghton mark houghton is online now
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Join Date: Jul 2008
Location: Central Washington State
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Originally Posted by mark houghton View Post
Violent and hard jolt shutdown is not just a stutter or hard miss. Can't miss this overboost protection symptom. Did your boost gauge show you as overboosting? If you were overboosting, then find the reason: look at the wastgate for malfunctioning....either a stuck valve, ruptured diaphram, or disconnected air pressure feed hose. If you weren't over boosting, then most likely it's the boost sensor going bad.
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Mark, I'm having a similar issue to Richard. Definitely the dashboard in the face experience. The background is:

Recent engine overhaul
Replaced fuel filter / accumulator
Electrical - fuel pump regulator replaced

The funny thing is that it happens at 1.1 bar and it has also happened (although less frequently) at .5 to .6 bar. I had an issue this weekend with a squealy fan belt. I tightened it and took it out for a spin. A previous owner had installed a VDO boost pressure guage where the clock originally went. The guage has a historical peak line. Well, it always sat at 1.1 bar. After a little fooling around on the autobahn tonight I noticed that the bar now sits at 1.22 bar. Hope I didn't screw anything up. I definately didn't notice anything wrong on the drive home.

So, I'm wondering 1. if I'm overboosting, 2. if it's a wasgetate issue that you mention above or 3. a combination of both?

Any ideas here? I'm really hoping for an easy, inexpensive fix. Still trying to ease the wife after the overhaul price . . .

Thanks in advance for your help,


Matt, you need to put specifics for what you're driving in your signature. That helps with the first part of diagnosis.

Did the previous owner set your car up for higher than stock boost? If you're seeing 1.1 bar, then I suspect it may be running with a 1.0 bar spring in the wastegate. Hopefully it also has the necessary modifications to support that high boost. If it's shutting down at 1.1+ bar, then I would say the system is doing as it's designed to do.

If it's shutting down at .6 bar, then either the gauge is faulty and you're actually boosting more than that, or something with the fuel delivery (overboost protection sensor, OB relay, or maybe simply the fuel pump fuse and/or relays up front). Pull the two relays and the single fuse, clean all contacts and look for signs of overheating, etc. These cars won't run on a single fuel pump, so even just one of the relays could be jiggling loose/loosing contact.

If your car wasn't intentionally modified for higher boost, then you do need to look at the wastegate because you shouldn't be able to reach 1.1 or 1.2 bar. Make sure the pressure hose from the intercooler to the WG is in good condition and tightly connected. If everything is stock and you're still overboosting, then I would suspect the WG diaphram is torn.
Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 05-17-2009, 04:52 PM
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