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NG900 & OG9-3 Performance, Mods & Tuning Covers Tuning & Performance modifications for the NG900 (1994 to 1998) & OG9-3 (1999-2002) & '03 Convertible

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  #1  
Old 28th December 2004
Schabs Schabs is offline
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Default Dawes boost control & the APC (BPC valve)

Does installing a Dawes manual boost control essentially "bypass" the APC (BPC valve)? I believe my APC is not functioning properly causing a "bucking" at high boost lower RPM. (I've had other posts regarding this problem)
I was considering the addition of the Hybrid Dawes, but don't want to buy a new APC if it becomes obsolete.
Thanks
Dave

Last edited by Schabs; 28th December 2004 at 07:33 PM.
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  #2  
Old 28th December 2004
Asia Skyly Asia Skyly is offline
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I am not sure I understand the problem you describe in detail. The Dawes devices does not bypasses the valve; it works in conjuction with it. I cannot remember the name of the three lines (W-Wastegate Actuator, I-Intake, C/R-???-cannot remeber and I am going from memory).

Essentially the device attaches from the BPC to the Wastegate actuator. You remove one of the lines and close the cycle by connecting one of the remaining lines back to the other "nipple" making a loop. This is one possible set up and there are several.

Under normal circumstance the car will never boost into the red in 1st or 2nd gear. With the Dawes device you can bypass that and actually get boost in those 2 gear.

The trick with the device is to set it to a level that will allow you the maximum boost while NOT incurring into any cut off from the ECU. This is the hard part, and I did mine strictly from trial and error in an empty industrial street

I am not sure I answered your question, so let me know if I can help somehow.
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  #3  
Old 28th December 2004
Schabs Schabs is offline
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My problem seems to be a fuel cut off. I inspected the lines for possible breaks/leaks and do not see anything. This symptom happened to me once before and it was a broken vaccum line. (The only line I found broken was for the PCV valve and fixing it didn't correct it). When under high boost, the car bucks as if it's cutting fuel. At EEuroparts.com it shows the BPC and says that it is the most common malfunction of this sort of thing. I didn't want to replace it though if the Dawes "took it's place". Since they work in unison, I think I'll replace the BPC.........hopefully that works and then move forward with the manual boost controller.

How can I "test" the BPC prior to replacing? I had a response on another post but didn't understand. Is there a way to test the waste gate?

Last edited by Schabs; 28th December 2004 at 08:59 PM.
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Old 28th December 2004
Asia Skyly Asia Skyly is offline
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That is interesting. The most common problem with the BPC that I have read about was not cut-off from the ECU but lack of boost! But you are right, and I would trust Eeuroparts more than me.

Here is that description from Eeuroparts.com:

Part Description:
APC boost control valve for any 2.3L turbo 90-98 9000, 2.0L turbo NG 900 94-98, and all 9-3 models( incl VIGGEN). This is the most common cause of underboost(needle won't go past middle yellow), and overboost(fuel pump cuts out when needle goes 2/3 into the red). Genuine Saab.


Usually the common test for the BPC is you disconnect the line that goes to the wastegate actuator, when you accelarate without the line to the WA you will get a boost in any gear (1st and second included!), but the ECU will trigger the fuel cut off. In essense the BPC limits the excess presure and it sounds just like what your problem is. Of course, this is the test for underboost, and you have the exact opposite problem!

Have you checked the line from the Turbo to the Wastegate actuator and from the Actuator to the BPC? They can get crummy in their old age. In fact have you carefully followed the three lines from the BPC?
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  #5  
Old 28th December 2004
Schabs Schabs is offline
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This is driving me nuts! But then again that part of the fun of figuring this stuff out.
I just replied back to Stalker in my other post "Fuel cut off at boost.." regarding this.
Check out my results by disconnecting the wire harness on the BPC. I think she's bad.
Dave
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  #6  
Old 28th December 2004
Asia Skyly Asia Skyly is offline
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I saw your reply and I guess the BPC is as likely of a candidate as anything else. When mine died, I had the exact opposite problem the car would not boost at all! However, if you do not have a crack in any of the lines from the BPC, I guess we should then blame the BPC.

This would be the first time I read about a BPC causing over boost, but there is always a first time for everything!
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  #7  
Old 29th December 2004
toenail toenail is offline
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The Dawes MBC can/does bypass the BPC depending on the method of installation you choose. If you drive a T-5 car, bypassing the MBC is the more common method used. It is considered a very cost effective way of replacing a faulty BPC. Many have gone this route, including myself, with excellent results and little downside.

Most BPC failures (including mine) that I've read about leave you with the car defaulting to base boost, around 5-6 psi in all gears. If your BPC is the culprit you can replace it with a Dawes Device and set it to anything below 15.5 psi in any gear. You should take appropriate steps to account for increased boost pressures (do a search for MBC+A related posts) such as larger exhaust, remove restrictions in the intake and exhaust paths, assure proper maintenance has been performed etc. If the BPC was not the culprit you will most likely have the same issues with the Dawes Device in place.
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Old 29th December 2004
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bkrell bkrell is offline
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I moved this to performance since even though it's really maint. related, you will probably get more insight into turbo-related issues in here.

An MBC will solve your problems IF the bypass solenoid is the issue. It's relatively cheap to get an MBC verses a bypass solenoid, so that would be my tact. I'm sure someone knows a procedure for testing it out if you want to make sure. Also try a forum search here and in the workshop under bypass valve or solenoid. Of course, an incorrectly set MBC will cause you to get a fuel cut. But if you are able to tune the MBC to the point where you are no longer hitting one, I would imagine the BPV WAS the issue. THe ideal thing for you to do would be to find another saab owner up there with an MBC so they can correctly test it out on your car.
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  #9  
Old 29th December 2004
Schabs Schabs is offline
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Quote:
Originally Posted by toenail
The Dawes MBC can/does bypass the BPC depending on the method of installation you choose. If you drive a T-5 car, bypassing the MBC is the more common method used. It is considered a very cost effective way of replacing a faulty BPC. Many have gone this route, including myself, with excellent results and little downside.

.
Thanks.
How do I know if it's a T-5 car or not? Not sure what that means. Also, I'll call Dawes today to make sure they provide the directions in terms of bypassing the factory BPC. I really would rather not buy a new $200.00 part if it's gonna be bypassed anyway.
Dave
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  #10  
Old 29th December 2004
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bkrell bkrell is offline
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Oh, it's very easy to install an MBC. The directions are here and on Dawes website. T-5 cars are Trionic 5 engine mgt. system. It's the system that uses the red colored DI cassette on the top of the engine. All turbo 900 models from 94-98 were T-5. The 99 9-3 was also T-5.

And absolutely, using an MBC will render the bypass solenoid useless.
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  #11  
Old 29th December 2004
Schabs Schabs is offline
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That's what I wanted to hear!
Just placed my order for the Dawes Hybrid controller, with new lines too to be safe.
In the meantime, I'll have to take her easy with the "believed to be" faulty BPC.
Dave
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