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Discussion Starter · #1 ·
Alright i dunno what this problem could be and i've asked quite a few people and i havent got a solid answer. Alright say im driving on the highway and i decide to downshift into 3rd or 4rth, now mind that this does not occur evertime, all of a sudden the car will just buck ! between like 3-4000 RPM. I dunno what the problem could be, my friend mentioned fuel cut-off. Does anybody have an answer for me! This has been a problem thats been bothering me since i purchased the car. PLEASE REPLY!
 

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HNNLIC
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Sounds like fuel cut off.

Check around in the engine bay to see if there is MBC of some sort. Should have a vaccume line leading from it to the turbo, and can be adjusted.
 

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Discussion Starter · #3 ·
Now what do you mean by MBC? Do you mean manual boost controller, as in an after market product or what the factory provides?
 

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HNNLIC
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Definately aftermarket. When you hit fuel cut off...your boost levels are spiking to 15.5 psi. Usually our cars are stock with a max of 12 psi of boost. From the sounds of it, your boost level has been increased. The usual object that can increase this boost level is a manual boost controller (MBC)..which is tuneable. This is why I think you may have one.

Look for either something brass or blue connected to the vacc lines around your turbo.
 

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Discussion Starter · #5 ·
I have to tell you there is nothing aftermaket on any of the lines. You think maybe the acuator on the turbo was messed with, because the guys at the local saab dealer told me you adjust boost to an extent with the acuator.
 

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HNNLIC
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I doubt anyone has messed with the actuator. Maybe someone else knows whats going on.
 

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he should not be hitting fuel cut at 3-4000 rpms, given i don't have a turbo, but i have a friend with one and i know a bit about them, but given highway speeds, and rpms, he should not hit fuel cut.

my question for you is, when you downshift to accelerate, do you hold the clutch in and rev it up to what the rpms should be at, when in that gear at that speed, and when you are reving it, do you release the clutch as the revs are climbing? if you do not give it gas before releasing the clutch, that would defiantely give you the bucking motion, because the engine with clutch in at any speed is around 1,000 rpms, now at say 70 mph in 3rd or 4th gear will yeild in rpms that are much higher than 1,000 rpms, and if you just release the clutch without getting the rpms up to what they will be at when the clutch is released, then your car will buck from the enine picking up to speed, this is not to good for the car.

~justin
 

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Discussion Starter · #8 ·
The thing is, it's not just when i downshift, it happens when i am accelerating. It tends to be third and fourth gear.
 

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is it just one jerk motion, or is it multiple like it's bouncing off a limiter of some kind?

does it continue after you pass a certain rpm until redline?

is it violent or subtle?

~justin
 

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Discussion Starter · #12 ·
It's just one pretty violent jerk, then if i get on the pedal too fast and too much it will do it again. Then most of the time when it happens ill be light on the pedal and push it down slowly and ill just continue to accelerate. Then on the other hand sometimes it doesn't even happen! So it's pretty unpredictable.
 

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HNNLIC
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Yea thats exactly when mine hits cut off. I think Tweek is right on the money...your APC may be going.
 

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i don't even know what the hell apc stands for, i always thought it staned for american products company, for the ricers, lol

i've got no answer for this one, so good luck with your troubles

~justin
 

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Discussion Starter · #18 ·
Somebody on this forum has to know what the APC is and what it stands for????/ PLEASE REPLYYY
 

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APC : Automatic Performance Control.

A Saab invention, this neat little boost-control setup listens to the motor for knock, and lowers boost accordingly. Therefore, the engine becomes low-octane tolerant! The APC System was introduced in the 1983 Saab 900 Turbo, hearalded by Saab as "The next generation of turbocharging".

APC was integrated with the ignition system on the 1990 9000 turbo, (DI/APC) and that was integrated with the fuel-injection system in '93 to become the famous Trionic system ('cause it performs 3 functions - boost / injection / ignition)

Your car has Trionic, where the APC is intertwined with many other things, so basically there is just a little wastegate actuator on the turbo and that's all of the APC system on a Trionic car. There is also a knock sensor on the block, that the Trionic computer sometimes uses to control boost.
 
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