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Turbo 1.2 Bar boost limit

T

tref

PCGB Member
Member
Can some-one remind me, or point me in the direction of an existing thread, of what causes boost to be limited to 1.2 Bar? Car is otherwise fine, just not getting full boost (and yes, that is 1.2 Bar absolute, 0.2 Bar actual boost before we start that confused conversation again!).

TIA,

Tref.
 
Nope, I mean 1.2 Bar absolute, 0.2 Bar above atmospheric... i.e., barley boosting at all... I normally expect to see it boost up to around 1.8 Bar (absolute again). The car is standard, no boost enhancers, nothing... all as it came from Porsche... so should be easy enough to analyse. I know this is some electonicery to prevent damage because something, somewhere isn't as it should be, but cannot remember what that something is!

Regards,

Tref.
 
yes, triggering the overboost protection would limit you to around 0.4 but switching the ignition off and on returns you to full boost. Check out Pauls suggestions or an a loose pipe / stuck open wastegate / dead turbo,
Tony
 
Thanks guys,

I really should remember to look at Clarks Garage first! I tried switching ignition off an back on, that didn't make a difference, so not overboost protection...

It has just occured to me though that I haven't really driven the car since changing the belts... so, more than likely a minor leak, or I have forgotten something somewhere...

Thanks again,

Tref.
 
My car ran 0.2 bar when Jon disconnected the cycling valve and ran the pipe straight through to the waste gate (for running in) could it be a failed/stuck cycling valve?
 
I see.
I'd had the same problem and had the wastegate switched for a new dual-port one, amongst other things, which solved the problem.
The cycling valve (Is this the 'blow off valve' in Jap car terms??) is the other (much cheaper) problem area.
 
ORIGINAL: nags

(Is this the 'blow off valve' in Jap car terms??)
Click to expand...

No - the cycling valve is the component that physically controls the standard wastegate when the KLR computer tell's it to. There's an overview of it here:

http://www.clarks-garage.com/951faq.htm#function

It does specifially mention that when it fails the max boost will be 1.2bar (I am presuming this means absolute pressure, so in reality is 0.2bar boost)

Off topic - the blow off valve is also known as the dump valve and sits between the turbocharger and the airfilter box

 
or the pressure sensor has failed. There must be one somewhere although it is not mentioned in that article. The reason I say this is that my old Saab 900 turbo had the APC system which does the same thing as KLR (it was actually a Saab invention back when they where a real car company rather then just tarted up Vauxhalls). Many many ppl used to replace the cycling valves thinking this was the problem when in fact sticking or failed pressure sensor was common and limited the boost to the safety level. I learned the hard way by buying a new cycling valve and seeing no difference.

If you can hear the valve clacking away then it is working, might be worn and leaky though which is a different issue but I doubt this would limit the car to anything like 1.2 bar (as a side note I compared a brand new Saab made by Bosch cycling valve to a 130K mile one and didn't see any boost difference on the dash)
 
The pressure sensor is inside the KLR housing itself and is fed by a narrow white nylon pipe.
 
My car had exactly the same symptoms and it was the cycling valve. V.easy check in Clarks Garage.
£70 from Porsche or I am pretty sure is the same unit as a sierra cosworth at half the price,

Do a search on ebay for "amal valve"

Rich
 
Sounds like the wastegate is getting direct boost pressure from the pre intercooler pipe, rather than the cycling valve doing its job of applying a slight vacuum to the wastegate to keep it closed until you approach the boost limit.

If you need a cycling valve tref, give me a call, i probably have some used ones.
 
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