Follow-Up: my boost problem seems to be temperature related ...

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

Reply to
Zon
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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

Reply to
Alan Cole

Yes, cold air is denser than warm air at the same pressure, and it's the mass of air that counts. However, the boost problem as described seems more of all-or-nothing, hence it is more likely a control problem. This again splits into two; either a control mechanism overreacts to temperature or the cooling system is at fault.

Reply to
Johannes H Andersen

And I guess thin air / high altitude does not make it any better....

Do you think these to together could cause this severe lack of boost? Gauge goes only up to half of yellow scale when problem persists. And in that one day I mentioned before, I went only to the border of white/yellow range.

No, everything's stock. Even tail pipe is standard :)

I guess I need to check hoses once again. As fas I know, engine is not overheating. At least standard temp gauge show normal temperatures, always.

How do I get rid of that?

BR:Z

Reply to
Zon

temperature

Yes, It is more or less on-off type of thing that starts when engine gets hot. That happens more easily on hot days. When problem occurs, boost gauge goes only up to mid-yellow, not to yellow-red border as normally.

Could this be just a combination of hot temperature, hot engine and thin air (high altitude ~ 1700mASL) ?

Or what should I do?

BR:Z

Reply to
Zon

There are various fuel additives you can buy made by STP, Forte, etc, that claim to de-coke your engine. Giving it a good thrash from time to time will help stop them building up in the first place.

There's some more info here, scroll down to point 10:

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BTW, the old fashioned way on carb engines was to spray a small amount of water into the carb while someone revved the engine. The water turns to steam and you basically 'steam clean' the inside! :)

Good luck, Alan

Reply to
Alan Cole

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