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89 turbo shuts down at about 5000 rpms

I have a 1989 turbo and it runs smooth and comes on boost just fine then at about 5000 rpm it is like someone flips a switch and it falls on its face. I almost hit my head on the steering wheel. When it falls I also get a puff of blue smoke on deceleration. My first thought was a bad rev limiting rotor but it has a standard rotor. The car does not quite it just comes off boost real fast. Any ideas?
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1999 Boxster
1980 911 SC Targa
1975 914-6 GT clone
72 911 RSR clone (needs full restoration)
2008 Yamaha Apex 375 hp@17 psi boost 525 lbs
Old 04-17-2014, 07:32 PM
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…this was something i went through, and found it was the stock rubber intake boot collapsing under pressure…it was pricey, but i replaced it with fabspeed's silicone unit, and haven't worried for my teeth since…good luck, hope this helps...
Old 04-17-2014, 07:59 PM
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I'll check that tomorrow. Thanks
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1999 Boxster
1980 911 SC Targa
1975 914-6 GT clone
72 911 RSR clone (needs full restoration)
2008 Yamaha Apex 375 hp@17 psi boost 525 lbs
Old 04-17-2014, 09:22 PM
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Quote:
Originally Posted by wholio94112 View Post
…this was something i went through, and found it was the stock rubber intake boot collapsing under pressure…it was pricey, but i replaced it with fabspeed's silicone unit, and haven't worried for my teeth since…good luck, hope this helps...
exactly. pricey? i think i paid $40 for a new one. mine did not have the port for the diverter valve so i ordered one with it.

squeeze the ruber boot, it should be very hard.

if not that you might look into fuel, maybe the filter. then i think i would make sure both pumps are running
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Last edited by T77911S; 04-18-2014 at 04:05 AM..
Old 04-18-2014, 04:02 AM
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Quote:
Originally Posted by hasaramat View Post
I have a 1989 turbo and it runs smooth and comes on boost just fine then at about 5000 rpm it is like someone flips a switch and it falls on its face. I almost hit my head on the steering wheel. When it falls I also get a puff of blue smoke on deceleration. My first thought was a bad rev limiting rotor but it has a standard rotor. The car does not quite it just comes off boost real fast. Any ideas?
By your description it sounds like the classic "face in dash" syndrome indicative of your overboost circuits kicking in and shutting off the fuel pumps. Could be your overboost sensor switch has aged to the point where it's tripping too soon under normal boost, or your wastegate isn't opening correctly and you are overboosting. What does your boost gauge say when this happens?

If it's just a bad OB sensor, simply replace it. Brand new, they shouldn't cut power to the pumps until you reach something like 1.2-1.4 bar of boost.
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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 04-18-2014, 05:27 AM
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Hi,

I have found I have the exact same problem.
I took my 1988 ROW 930 out last weekend for it's first run out since October 2013, I let it warm up for 16 miles or so than gave it a boot full, it came on boost with the usual surge of power but a 5000rpm it made a slight pop noise (not as loud as a backfire) and I nearly lost my front teeth on the steering wheel as it almost stopped mid surge. Then as quick as it stopped it carried on as normal but without any further boost.

I tried this a couple more times, each time with the same result. What I did notice was a slight periodic whistle as I was driving even at normal speeds, I checked but it wasn't a brake binding. I also noticed that when I accelerated hard the boost gauge needle didn't move straight away but when it did move it flipped around to 1.0 bar + almost instantly as I got the slammed on brakes feeling.

I've had the car 8 years and whilst I have driven it hard at times I've never had it show over 0.8 - 0.9 bar before.

Would this be the same issue as hasaramat is experiencing and should I be looking at the same fixes?

Many thanks in advance for any advice.

Regards

Dan.
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Old 04-23-2014, 02:12 AM
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Yellow Relay from Hell...to finally solving the problem

For me older car was this
Unknown sending unit

GL
Old 04-23-2014, 06:02 AM
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Take the white wire off the overboost sensor and ground it. See if the problem goes away. If it doesn't it's something else like suggested above.
Old 04-23-2014, 06:25 AM
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Thanks All,

I'll try the white wire off the overboost sensor first, then work my way through the other suggestions if that doesn't work!

I'll report back after the weekend.
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Old 04-23-2014, 08:03 AM
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UPDATE! Boost sensor was already grounded so that was not the problem. The rubber elbow hose from the sensor plate to the hard intake tube is swollen and soft. Looks like that might be the issue.
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1999 Boxster
1980 911 SC Targa
1975 914-6 GT clone
72 911 RSR clone (needs full restoration)
2008 Yamaha Apex 375 hp@17 psi boost 525 lbs
Old 04-25-2014, 08:05 AM
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Quote:
Originally Posted by JFairman View Post
Take the white wire off the overboost sensor and ground it. See if the problem goes away. If it doesn't it's something else like suggested above.
I have had this problem recently. In my car, it was manifested as a (no) warm start problem. I went through all this other stuff and thought I had fixed it. But then last week it developed into an intermittent complete no-start problem. I took it to TRE, where they figured out it was the overboost sensor cutting off power to the fuel pumps. So we jumped/bypassed the sensor and the car starts perfectly. A new switch is on order. In the meantime I just have to remember that right now I don't have an intact overboost sensor, so I'm driving the car and shifting based upon the notoriously unreliable boost gauge, as opposed to the tachometer.
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Old 04-26-2014, 09:59 PM
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Good but slightly embarrassing news from the weekend!!!

Whilst looking around under the intercooler for the overboost sensor, behind the main cast alloy pipe I spotted a small (1/2" diameter) rubber vacuum/breather hose to the underside of the intercooler was disconnected!!

I reconnected this, took it for a good shake-down and i'm happy to report that boost is working as normal and no intermittent whistling can be heard.....doh!!

Whilst under the intercooler I checked the sensor and i'm also happy to say the white wire is connected to the sensor......happy days

Thanks for all the suggestions and technical help though fellas.

Regards

Dan.
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Old 04-29-2014, 12:48 AM
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