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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > Low boost?



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      08-28-2010, 07:55 PM   #1
meepster
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Low boost?

About 2 months ago I had a wastegate rattle problem (identified by the dealer) and they performed the first step in the SIB - software update from the original 29.x 2007 E92 software. Afterwards the car definitely sounded better (exhaust note), but it felt a little weaker on the WOT pulls than prior. Unfortunately I didn't have anyway to check the boost prior to or right after the change. Recently I got a kiwi wi-fi and Rev on my iPad. I took a few measurements today and was really surprised to see the max boost was ~2.7 PSI. Is that anywhere close to normal? Below is the data from the Rev software.

Note - I'm bringing it back in next week due to the wastegate rattle problem persisting and plan to mention this. Just curious for thoughts from others.
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      08-28-2010, 08:08 PM   #2
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I'm not familiar with how the KIWI device works exactly, but can you explain what the difference is in Boost and Intake Manifold PSI is? Also, what tune (if any) are you running?
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      08-28-2010, 08:18 PM   #3
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Quote:
Originally Posted by jblackwell View Post
I'm not familiar with how the KIWI device works exactly, but can you explain what the difference is in Boost and Intake Manifold PSI is? Also, what tune (if any) are you running?
I believe it's the value read from the MAP sensor in the actual intake and is absolute vs. relative. So this would be the absolute pressure of the air within the intake manifold after it's gone through the intercooler but before getting to the throttle body. I think the average sea-level air pressure is ~14.7 PSI, so this is just the relative boost added to that.
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      08-28-2010, 11:46 PM   #4
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How does your car feel? Do you have a tune at all?

You really need to know the answers as they are an important part of diagnosing a problem that may or may not exist.
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      08-29-2010, 12:32 AM   #5
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Quote:
Originally Posted by jblackwell View Post
How does your car feel? Do you have a tune at all?

You really need to know the answers as they are an important part of diagnosing a problem that may or may not exist.
The car feels fine, just a little light on the acceleration compared to where it was a bit ago. I haven't done any engine tuning/mods, just Dinan Stage III Suspension. I'll see what the dealer says, going to mention I saw low boost on my OBD scanner and see what they say...
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      08-29-2010, 03:08 PM   #6
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Your car would feel VERY slow if it was only boosting 2.7 psig. You should be getting low boost codes at that level.

My guess is your datalogger isn't reading quite right.
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      08-29-2010, 06:49 PM   #7
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The intake manifold sensor does not read boost for the most part; you hit the ceiling of that sensor. The intake tract sensor reads boost.

The manifold sensor is mainly for determining vacuum values.
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      08-30-2010, 01:16 AM   #8
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Your car would feel VERY slow if it was only boosting 2.7 psig. You should be getting low boost codes at that level.

My guess is your datalogger isn't reading quite right.
Interesting, I'll hook the kiwi + rev up to my friend's e93 335i and see if it's the same. My guess is you're right.
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