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Falnaim 06-10-2012 09:06 AM

NEED HELP PLEASE: Engin jurcking & losing the power around 4000 + RPM
Hello There,

I have 1987 930 turbo just rebelled the engine and have new Alternator, Fuel pumps, Alternator Fan, Faabspeed "Headers, Mufflers, Air Intake, Intercooler", Tial W/G with a 1 bar spring, A/C kit.

When i drive the car Engin jurcking & losing power after around 3900 to 4100 RPM then i replaced the Distributor Cap, Ignition Wires & the Coil Wire with new set and still having the same problem but "more power with engine" as 2 of my Ignition Wires was broken.

Please can any one help me what to do ?

Thanks and Best Regards,


einsteiger 06-10-2012 09:49 AM

I recall a very similar situation with another 930, but I cannot remember on which forum I saw it! :o

I'll try to find it and link it here. This person also had to deal with power falling off after 400 RPM.

Falnaim 06-10-2012 09:57 AM

Thanks einsteiger

RarlyL8 06-10-2012 09:59 AM

I'll throw in a few suggestions even though you used the F word, ha!
HOW does your engine falter at 4K? Teeth in glass, bucking, or slow power loss?
> Teeth in glass - overboost switch activated
> Bucking - fuel pump, ignition
> Power loss - BOV, fuel pump, O-rings
These are generalities, need more info to hone in on it.

Falnaim 06-10-2012 10:26 AM

Thanks RarlyL8

when I mentioned " power cutts of " dos not means (as in engine stops ) it jurcks & los the power.

totle 06-10-2012 11:22 AM

Sounds like the overboost switch is failing. Had similar problem on my previous 930.
You can test by connecting the wire to ground and try. If all is good then, you need to replace the overboost switch. It is located under the IC in the BOV housing

RarlyL8 06-10-2012 11:24 AM

Bucking/Power Loss - check the easy stuff first, O-rings and vac leaks.
> Check timing / ignition function
> Check fuel system pressure and flow
> Factory BOV? Pull and check gaskets and piston

Kevin may have seen my post last week on the failed BOV. After replacing the gaskets I was not expecting the piston/spring to be hanging up in the bore but they were due to oxidation of the surfaces. The symptoms I had been experiencing were bucking and loss of power at full boost.

Tt surgeon 06-10-2012 11:27 AM

Question, if you convert to long neck, do you lose the ovrboost switch?

RarlyL8 06-10-2012 11:30 AM

No, the overboost switch should screw into the long neck intercooler.

totle 06-10-2012 11:31 AM

I think when going to long neck overboost switch is connected on the intercooler

JFairman 06-10-2012 11:47 AM

I've experienced that when it was getting too much fuel on boost. I have the Brian Leask adjustable WUR or control presure regulator and it needed boost control pressure raised a little bit to fix it.

You need a wideband air fuel ratio gauge or control pressure gauge on board to diagnose that.

Falnaim 06-10-2012 11:58 AM

What is BOV ?

totle 06-10-2012 01:07 PM

Blow Off Valve

Tt surgeon 06-10-2012 01:11 PM


Originally Posted by Tt surgeon (Post 6796812)
Question, if you convert to long neck, do you lose the ovrboost switch?

you don't happen to have a pic do you?

908/930 06-10-2012 04:49 PM

When rebuilding, is there any chance that you swapped the two vacuum hoses to the pots on the distributer?


RarlyL8 06-10-2012 06:51 PM

Swaping vac ports on the dizzy won't make any difference when on boost. Both ports connect to the throttle body just in different locations, above and below the throttle plate.

Jim getting too much fuel on boost is not a typical situation, they can choke on the midrange of a stock engine with a failing WUR. This engine is modified so I would expect it to go lean. Good point on the AFR gage, great tool needed in this situation to help see what's going on.

Ronnie's.930 06-10-2012 07:03 PM


Originally Posted by Tt surgeon (Post 6796936)
you don't happen to have a pic do you?

Post #9 pic #5 of this thread -

cuchanonM 06-10-2012 07:26 PM

I'll try to find it and link it here.

Tt surgeon 06-10-2012 08:05 PM


Falnaim 06-26-2012 07:45 AM

Problem Solved
I replaced the Over Boost Switch And Or Pressure Sending Unit For Turbo Boost Gauge.
Parts Number:-

My car is working now perfectly :D.



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