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930 Cutting out

I have an 89 930 LE which has started cutting out under boost which produces a very violent and hard jolt in the engine. Back off the throttle and the engine splutters and then gets running normally again at lower revs. It only happens when the turbo has just started spooling up and I am starting to accelerate hard. I had two thoughts. Either the coil is packing up or the boost pressure switch is faulty. Has anyone encountered this before and have any other suggestions where to track it down. Thanks. as you will guess-not overly mechanical!
Old 05-13-2009, 12:59 AM
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Originally Posted by RichardE View Post
I have an 89 930 LE which has started cutting out under boost which produces a very violent and hard jolt in the engine. Back off the throttle and the engine splutters and then gets running normally again at lower revs. It only happens when the turbo has just started spooling up and I am starting to accelerate hard. I had two thoughts. Either the coil is packing up or the boost pressure switch is faulty. Has anyone encountered this before and have any other suggestions where to track it down. Thanks. as you will guess-not overly mechanical!
Try replacing the fuel pump relays and fuse (singular).

Regards, Dave
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Old 05-13-2009, 03:16 AM
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Also look for a loose connection or leak in the intercooler to wastegate signal hose.
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Old 05-13-2009, 04:01 AM
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cutting out under boost which produces a very violent and hard jolt in the engine. Back off the throttle and the engine splutters and then gets running normally again at lower revs. It only happens when the turbo has just started spooling up and I am starting to accelerate hard
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.

If you've got the tools on hand, you can test the boost sensor by taking it out of the car, hooking an ohm meter to it, and applying air pressure. It should "trip" (lose continuity) at something like 1.2 to 1.4 bar. If that sensor (just a switch actually) opens at a lower pressure, it may be going bad. A $50+ part through our Host.

Another diagnostic thing you could do....but only if you have confidence that you are not overboosting and trust your boost gauge, would be to disconnect the single wire from the boost sensor and connect it to ground. That will take the overboost protection feature out of the equation. As long as nothing else is wrong, you should be able to boost into the stratosphere...or until your engine melts down. If the wastegate is functioning properly, it will control the boost to .8 maximum. If not, you will overboost but the engine will not shut down. What you're looking for is to see if the engine is shutting down earlier than .8bar for reasons other than the protection circuits. If you try this, pay very close attention to the boost gauge and get off the throttle when you reach .8bar.
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Last edited by mark houghton; 05-13-2009 at 05:04 AM..
Old 05-13-2009, 04:56 AM
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Sounds like she's running outta fuel. Check for unrestricted fuel filter and low system fuel pressure (bad fuel pump [s]).
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Old 05-13-2009, 05:56 AM
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Check the boost vacuum lines running to the wastegate area and the intercooler hook ups and such just to make sure that the CIS is not leaking air.

If your boost lines have a hole in them to the wastegate, that could cause your engine to overboost by not triggering the wastegate quicly enough and the boost cut off switch might be triggered.

Otherwise I am guessing fuel delivery.

Bad gas will make your engine run funny but not just on boost, more like randomly you will get little sputters (like a carb out of tune). I had this problem but it worked itself out when I used new gas.
Old 05-13-2009, 08:06 AM
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"dash in the face" syndrome is impossible to miss. This sounds like overboost safety switch tripping. It should cut at around 1.1 bar. What boost did you run when car started to jolt? If it's tripping at over 1.0 bar then car is overboosting. Make sure your wastegate is working. Do not try bypass the switch, or you might end up will expensive problems. The switch is there as last stand, if everything else fails.


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Old 05-13-2009, 08:58 AM
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Quote:
"dash in the face" syndrome
Hehe, I like that description. The first time that happened to me was a definite WTF moment.
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Old 05-13-2009, 09:40 AM
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Any black smoke coming out of the exhaust during the cutting out?

I had a bad WUR that was so rich during the onset of boost, it would buck like a bronco.
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Old 05-13-2009, 10:45 AM
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930 Cutting out

Hey, guys. To all of you who have taken a look at my problem and taken the time to help, a big thanks. I will have a poke around all those issues. Sounds like I'm not the first to have the problem. Just for the record, the cut out comes at about
.6 bar on the gauge so it's only starting to get cranked up. being an LE with basically the S set up it should have 1 bar boost so I don't think I am overboosting. Funny, I have just had a new fuel filter put in??? Interesting.
Thanks anyway. have to add that the 930 is the most fun I have evr had with my clothes on too. Aren't we all lucky!
Old 05-13-2009, 12:07 PM
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What about some pictures of the car? It might help identifying what's wrong with it...
Old 05-13-2009, 12:56 PM
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This happened to my 930 the fuel relays , One of them came apart when removed from socket . It had gray powder flash inside . Replaced and Wa La !!!
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Old 05-13-2009, 05:40 PM
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Ive experienced the same sputtering, jolting, hesitation and it was the spark plug wires. For me, it only happened under load, just as you described.
Old 05-14-2009, 11:46 AM
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...and the survey says....

Let's do a little survey:
How many of you have ever experienced a real-live over boost shutdown? Mundane words like sputter, stutter, jolt, miss, lurch, and hessitation just don't do it justice. More descriptive words like sudden, immediate, violent, jolt, cataclysmic, dash-in-the-face, instant shut down work better for me.

Richard, did this cause you to break your front teeth on the steering wheel when it happened, or perhaps give you a bloody nose or bloodshot eyes as you suddenly went from 2G's to negative G's? Did it make you want to shout "WTF was that!!!" as you looked in the rear view mirror for signs of piston rods exiting the engine?

All of the ideas offered up are good valid possibilities, and it sure is challenging to diagnose based on written descriptions. But I think everyone on this forum does a great job in that regard.
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Old 05-14-2009, 12:35 PM
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Yep, it was cataclysmic, Like it comes absolutely out of nowhere, at the point where the turbo is reeling, the nose is coming up and the hair is rising on the back of the neck - and then bang! It is a viciously hard thump and you imagine the crankshaft taking a real hiding. At least when the turbo is backed off the car can still run ok. Talking to my service guy there are, as you guys have all pointed out, a range of possibilities and most of them are a relatively cheap fix so here's hoping. Once again thanks, it's been agreat help.
Old 05-14-2009, 08:28 PM
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I am going away for a month so the problem won't be fixed until late June but i will post the outcome as soon as we know the answer.
Old 05-14-2009, 08:31 PM
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To test the over boost switch, would he just remove the wire to it or remove and ground it?

Dose the car have a HF or other modified turbo and or shortie headers?

Been any other mods or work done of late?
Old 05-15-2009, 06:30 AM
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Quote:
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To test the over boost switch, would he just remove the wire to it or remove and ground it?
If you do that w/o accurate boost gauge and are not gentle with gas pedal you might end up with turbo deadheading = knock = shattered piston rings & whatnot. YMMV...
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Last edited by beepbeep; 05-15-2009 at 12:58 PM..
Old 05-15-2009, 08:29 AM
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Quote:
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To test the over boost switch, would he just remove the wire to it or remove and ground it?

Dose the car have a HF or other modified turbo and or shortie headers?

Been any other mods or work done of late?
Remove the wire and ground it or the pumps won't run. Remember the switch is normally closed (making ground connection) and opens only after exceeding boost.

Beep Beep: When I made the suggestion earlier "...only if you have confidence that you are not overboosting and trust your boost gauge, would be to disconnect the single wire..." it's definitely a diagnostic approach not for the faint of heart. That's my disclaimer, anyway.
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Old 05-15-2009, 10:17 AM
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[QUOTE=mark houghton;4660820]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
Old 05-17-2009, 01:49 PM
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