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Jan 27, 2007 | 06:15 AM

Lowcountry

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Boost problem!

My car (before FMIC) used to peak at 23-24, and settle in and hold at 20-21. After FMIC, it was more like 21-21, holding at 18-20. This morning I tried to get my peak and hold numbers back up using the boost machine. I went up one full turn on the boost dial, which put me at about 5.5 turns. I then took the car out and ran it. I found that as soon as I hit 20psi, there was a sharp venting of air (sounded like it came from the DV/N75 area), and the boost immediately dropped to 15psi. I then turned the BM off completely, and drove about 10 miles. I then repeated the full boost experiment, BM still off. Same result. Sharp venting of air from DV area at 20 psi, quickly dropping to 15. I then re-lubed my DV, using synthetic grease. I retested. Same result. I hit 20psi, and boost vents out like I took my foot off the throttle (which I didn't do).
It sounds to me like I have a boost leak. I pressure tested my system just over a week ago, and everything was good. Heck, everything was good this morning until I started fiddling with my BM that hadn't been touched in months. I visually inspected the lines near the DV and N75, but didn't see any loose clamps or slits in the lines. Does anyone have an idea as to what is going on?
Thanks in advance.

Jan 27, 2007 | 06:37 AM

TTschwing

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2 potential issues..>>

Either a leak, which you seem to have ruled out, or the N249 venting boost because of another issue. The N249 can command the DV to dump boost (the sound you seem to hear?) if other sensor items are not up to supporting the requested boost. Low signals from the Temp sensor, MAF, bad gas/detonation etc. can all cause this. 1-2 psi Pressure loss with the FMIC addition is normal.

Jan 27, 2007 | 06:43 AM

petervan

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when my car had serious knock due to carbon build up from bad coil >>

she would vent boost at WOT as if I got off the gas.
Check for ignition retard due to knock?

Jan 27, 2007 | 07:08 AM

Lowcountry

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I'm not showing any codes other than post-cat 02 sensor reading (I have no cat right now)...

Nor am I hearing anything that sounds like engine knock, nor have I ever. I did just go fill up with different gas than I had in there, but the problem persists. I think it to be strange that I didn't have this problem until I fiddled with the BM and possibly set the boost to high? Would resetting my ECU help anything?

Jan 27, 2007 | 07:16 AM

Lowcountry

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Steve, is it the ambient temp sensor that you're referring to?

Jan 27, 2007 | 07:39 AM

TTschwing

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That has some impact too...>>

But rarely goes bad, although some have found them go missing. I assume you relocated it into a clear air area when you did the FMIC?
I was actually refering to the Coolant temp sensor

Jan 27, 2007 | 07:41 AM

TTschwing

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Asking for more boost..>>

Creates more heat which has an impact on how the ECU ultimately sets things. O2 sensor could be an issue too...The the rear checks on the front and they need to be in the same range for everything to work right..