Date: Sat, 22 May 2004 21:18:50 +0100
From: Alan Cole <>
Subject: Re: Follow-Up: my boost problem seems to be temperature related ...

Zon wrote: > I've been posting to this newsgroup about my intermittent boost problem and > you have helped me to limit possible causes to BPC valve or it's control. > Car is '99 9-3 FPT (185hp) > > I'm reluctant to invest $200-250 in a part that may be functioning > perfectly, so I haven't purchased new BPC valve yet. > However, I have had enough time to develop a feeling that the lack of the > boost is actually temperature related. It seems that when I drive engine hot > It starts to lack the boost. When engine bay get's extremely hot, I loose > all of the boost. Hotter the engine bay, lousier the boost. When I let it > cool down in shadow for several hours, it works more or less fine again. Hot > days seem to be worse than cool days. The worst day was when I drove engine > hot, parked it under the prairie sun for 4 hours, and when it was time to go > home I let it idle w/ A/C on for 5-10minutes to cool down interior while I > was collecting my stuff. When I headed back home, I had no boost whatsoever. > > So, now I'm thinking it is temperature related, and probably it is engine > bay temperature that counts. When the problem appears, everything under the > hood is hot, even BPC-valve almost burns my fingers. When I disconnect > wastegate hose from BPC-valve, I get the boost back. > > Can BPC-valve malfunction in such a manner that when it becomes hot, it > becomes sticky and leaks pressure to wastegate actuator? > > Or could one of the sensors start malfunctioning when hot, thus mislead > engine electronics to think there is too much boost? > > I haven't taken it to dealer yet, since the problem is intermittent. With my > luck, it does not appear when it is there, so they make a guess, charge me > couple of hundred dollars, send me home, and next day I find nothing has > changed. Been there done that. > > BR:Z > > It's well known that turbo engines don't perform as well as hot days. The higher the air temperature, the more likely you are to get knock, and when the ECU detects knock, it reduces the boost until the knock stops to prevent your engine destroying itself. All perfectly correct and normal. Have you got one of those 'performance' air filters sucking in air from the hot engine bay? Or maybe a leak in the air intake pipes allowing hot air to be sucked in? I'm assuming the engine itself isn't overheating. Another possibility is that after 5 years you have some carbon deposits that will make the car knock more readily. Good luck, Alan

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