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Discussion Starter · #1 ·
The boost pressure on my 1999 9-3 2.0 lpt (with BSR ECU upgrade and Forge recirculating dump valve) has lost boost pressure - down from around 1 bar to about 0.6 bar. The last thing I did before noticing the drop was to flush the injectors and use an oil additive (both Slick 50). Suspecting a vacuum leak, I changed all the pipes I could find. I have now shortened the actuator rod which gives 1 bar of boost which then drops straight off to 0.6. Performance is 25% off what BSR expect. Any ideas?
 

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I'd start by making sure your base boost is set to spec- 0.6 sounds high, and Trionic tends to adapt downwards if base boost is too high.

The fact that it drops down and doesn't go up and down rather suggests to me that it's probably not a mechanical problem with the actuator, and that possibly the ECU is seeing a problem at the top level of boost and backing off.
 

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Too me I looks like your ECU is dropping to base boost for one reson or another, could be knock, bad DI aso.
If you have your std ECU plug it in and see if the engine tolerates more boost than base boost.
 

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The ECU may be holding boost back because of whatever additive you may have used to flush the injectors. The ECU will pull back boost asa much as it can when it detects knock or is just not getting the readings it likes from the spark plugs. Additives will leave deposits on the plugs causing boost to be pulled back and performance to suffer.

I suggest running the fuel tank very low before refilling the gas without any further additives. Also, check the plugs for any funny colored deposits, and replace if fouled with anything other than carbon. I also recommend that you return your wastegate actuator to the original length as this is what your ECU was tuned for. If you have it set too high, the ECU may not be able to pull the boost back far enough if something does warrant it.

One last thing to note, I have had this same problem fix itself with a fresh tank of gas. That is why that is my first suggestion. Sometimes you may get some bad gas and it may be the only problem.

Good luck finding your solution!
 

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Discussion Starter · #6 ·
Thanks for the comments. I've done a long motorway run today, and with the actuator rod still shortened, max boost in 4th and 5th swings between 0.8 and 1.1 bar on full throttle (no increase in performance), but still returns to 0.6 in second and third at full throttle. The fuel additive was added 2000 miles ago and I always fill from near empty.

Since noticing the drop in boost, I've replaced the plugs and vacuum pipes, reverted to the original dump valve and the DI cassette is only 3 months old. No change.

I'm unclear what base boost is. Can someone explain?
 

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It may be a long shot but I had a similar problem recently where my boost dropped off over a week or so to absolutly nothing - less than base boost. Ttried all the usual like vac lines, new dump valve etc. Vincent on the site and Saab dealer suggested exhaust blockage (or partial) stopping gasses leaving and thus preventing turbo from spooling up. I replace both back boxes and sure enough full boost returned. I guess one of the silencers collapsed in on itself. I do not run a CAT but it is possible that this may be blocked.

Mike
 

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Originally posted by Chouet:
[qb]I'm unclear what base boost is.  Can someone explain? [/qb][/b]
The wastegate is held closed by a spring connected to a vacuum diaphragm or piston. Boost pressure from the turbo "Barb" on the pressurized outlet pushes against the diaphragm or piston and forces the wastegate open. The ECU can control how much pressure is against it by bleeding off some boost back into the intake through the boost pressure control solenoid.

Base boost is the maximum boost pressure that can be reached when none of the air is bled off. For instance if the line from the turbo barb is run straight to the wastegate actuator. Also, you should reach base boost if the solenoid is unplugged.

Base boost is related to how much "pulsewidth" the ECU needs to give the control solenoid to attain a specific pressure. While the ECU is adaptive, and can control the turbo even if the base boost is a little off, it's generally bad for performance.

Always worth a check. Easiest way is to unplug the solenoid. But safest way in my oppinion (if you know what you're doing) is to run the vacuum hose straight from the barb to the Wastegate Actuator. Just my two cents though. The vacuum solenoid should be in the "closed" position when de-energized, and thus would effectively do the same thing. But if the control solenoid is defective (which would cause similar symptoms) it might get "stuck open", which could result in exessive boost, and a quick trip to the fuel cut.

Dubbya~
 

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Discussion Starter · #9 ·
I haven't resolved the problem yet, but I'm learning a lot in the process (thanks everyone for the help!). The car is going on a rolling road in a few days - the fella at the tuning centre thought it sounded like a fuel delivery problem.
 
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