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Discussion Starter · #1 ·
When my car is pulling hard, sometimes the needle fips right round to the end of the red and the over boost cutout cuts in. (HUGE jolt as the car seems to stop dead in it's tracks, then lurches forwards again)
I have replaced the vacuum hoses and this hasn't helped. Any ideas?

Note, this isn't the normal dip into the red that happens when the turbo first spools up, it can happen after the needle has settled back to the edge of the orange/red, while running on full boost for a few seconds.

'94 9000 Aero
No chip (yet)
3" JT Cat Back Exhaust
Mark
:cheesy:

[edited to fix broken image url]
 

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it happens

before I started to tweak my aero it would do it occasionaly ,typically wot in third ...
still do not know why
my only thought is that the conditions strayed off the edge of the ignition/boost/fueling map and it failed safe
since I fitted (various) a MBC It will do it at will....
 

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Originally posted by ylee coyote:
[qb]before I started to tweak my aero it would do it occasionaly ,typically wot in third ...
still do not know why [/qb][/b]
One possibility is that the base boost is set too high. I had this problem on my Saab and it typically hit overboost at either 3000 or 4000rpm WOT in 3rd, sometimes in 4th, too.

Check base boost setting.
Check vacuum hoses for leakage (unlikely if new)
Check hose has not come off the wastegate actuator
 

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Gents, intrested to find out why a fault with the wastegate actuator would cause overboost ?, my car last year had the performance of a 1.4 focus , took it to my saab specialist , his garage was to busy but he said to check wastgate linkage, got car on pit at my work and true enough the pin had came out, replaced with "r" clip and had no trouble since
.Engage my brain
, r u saying that when the car reaches the level of boost when the actuator should open it is not ? hence giving overboost ?, what was happening in my case then ?
All these questions Haggag01
 

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if the wastegate is stuck in closed position, you will overboost.
if the link has come off, the wastegate is left open, no boost.
there is a spring in the actuator housing which, when working, allows the actuator to open and close the wastegate, giving you different levels of boost.
 

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Discussion Starter · #7 ·
Thanks guys, good to know it isn't just me.

I'll check that out next time I have me head wedged between the block and turbo

What is the easiest way to check this if I can't get it onto a ramp? can I see it from above?

Mark
 

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I had the same on my Aero, and was thinking wastegate, but it turned out to be a faulty BPCV (Boost Pressure Control Valve), which is the black plastic box fixed close to the top near-side end of the radiator, with 3 connections from it. Only way to check is to swap with a known good one, as they are about £120 if memory serves me right.
 

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hi
is ther no way of testing the BPCV valve apart from replacing it ?. iam have some mad things going on around that department. ie wineding waste gate rod in and out dont have no affect to bass boost
 

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Originally posted by lizard:
[qb]is ther no way of testing the BPCV valve apart from replacing it ?.[/qb][/b]
You could check the electrical resistance between the pins to see if the coils are intact (can't remember which pins to measure between) but you don't need a new one to test by substitution. Borrowing one from a car that's known to be working properly should be all you need.
 

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Resistance:

5 ohms between the two outer pins
2.5 ohms between either outer pin and centre

You should be able the blow through the C or W ports, but not the R

HTH

[edit] it's also known as the APC solenoid/valve
 

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Very safe... the valve is simply a wire wound coil. You can't damage it with a multimeter. Just unplug the connector.

As for blowing through the ports, somehow I doubt your lungs can get anywhere near the flow/pressure of a turbo spinning at 100,000rpm
 

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Mark,

I have had the 'brick wall effect' a couple of times at WOT in 3rd or 4th. I seemed to think it was when the APC system was self learning and just went slightly over boost. However, my boost guage does sit near the top of the red zone at full boost!

It hasn't happended since I switched to 98RON fuel.

Also, the APC valve- mine seems to make a faint buzzing noise at idle, which stops when you increase. This may be a simple way to check functionality??

Simon
 

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Discussion Starter · #18 ·
Good idea. I am running on Super Unleaded which I believe has a higher RON than normal unleaded. However I seem to think that the overboosting has happened more with this fuel. The car seems about 100 times more powerful with Super UL!
 

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Adding the comment I omitted to make earlier

Like many things on the Saab engine management system, I understand that the overboost cutoff is adaptive- if it happens, then it lowers the threshold at which it will next happen etc. etc... so a short term fix is to reset the ECU by disconnecting the battery or pulling the ignition system fuse in the underbonnet relay/fuse box.
 
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