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Discussion Starter · #1 ·
So normally I have pretty consistent boost after 2.5k rpm between 18-21psi. For maybe the past couple weeks it has been maxing between 5-13psi... But the odd thing is vacuum still reads as it always had, around 19-21 Hg. Is this normal for having a boost leak? I would have assumed vacuum would be weaker also if that were the case. I looked over all the easy accessible lines and the OTE pipe and everything I can see looks alright anyways. Any insights?

Thanks!
Bryan
 

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It's kinda obvious. If car feels slower you have problem with car. Else gauge/gauge hose?
 

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What kind of boost gauge are we talking? I know some people have had some issues here and there with the IPD gauge before.
 

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Discussion Starter · #4 ·
its a cobalt boost gauge, it doesn't feel all that slower. Could be wrong though, I can hear the turbo spooling just like it was when I was reading full boost.
 

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Full boost requires everything after the turbo being free of big leaks. Full vacuum only requires everything after the throttle being leak free, so if the gauge is correct I hope that helps you to track it down. As a way to check the gauge, use a compressed air source and another pressure gauge to see if they agree.
 

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Discussion Starter · #6 ·
Full boost requires everything after the turbo being free of big leaks. Full vacuum only requires everything after the throttle being leak free, so if the gauge is correct I hope that helps you to track it down. As a way to check the gauge, use a compressed air source and another pressure gauge to see if they agree.
Ahh yes this makes sense, this is my first boost leak so this should be a treat tracking it down..
 

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i'm in the same boat as you. vacuum is normal, boost not so much. what's your gauge showing?


Sent from my iPhone using Tapatalk
 

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Get a scan tool on the car capable of showing fuel trims. Torque app + bluetooth OBD-II scanner work great and not expensive. If your long term trims (LTFT) are way negative, particularly when you are out boosting the car pretty hard, you have a boost leak. Vacuum at idle is no indicator of a boost leak. Best way to detect is to do a boost leak test by using a compressor with 5 -10 psi and pressurizing the entire induction path starting downstream of the MAF. Disconnect the airbox/MAF and connect one of the aftermarket 3" boost leak testers to your Snaab intake pipe. Take off your oil fill cap. You will get leakage through the valves within the engine, but you should be able to detect a leak elsewhere. 10 psi works better than 5 psi IMO... just don't go crazy with pressure unless your compressor's regulator is reliable. Spraying soap out of a squirt bottle helps to ID a leak source. They can often be difficult to spot. FMIC plumbing couplings are common spots for leaks especially near the throttle body and at the turbo outlet. I recently discovered one on my turbo... bolt in the compressor housing backed out over time and created a major leak path! Major pain to find it as it was on the underside of the turbo.
 

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Discussion Starter · #9 ·
Get a scan tool on the car capable of showing fuel trims. Torque app + bluetooth OBD-II scanner work great and not expensive. If your long term trims (LTFT) are way negative, particularly when you are out boosting the car pretty hard, you have a boost leak.
I have vida at home that can do that I'm pretty sure. Where should the long term trims read regularly?



Best way to detect is to do a boost leak test by using a compressor with 5 -10 psi and pressurizing the entire induction path starting downstream of the MAF. Disconnect the airbox/MAF and connect one of the aftermarket 3" boost leak testers to your Snaab intake pipe. Take off your oil fill cap. You will get leakage through the valves within the engine, but you should be able to detect a leak elsewhere. 10 psi works better than 5 psi IMO... just don't go crazy with pressure unless your compressor's regulator is reliable. Spraying soap out of a squirt bottle helps to ID a leak source. They can often be difficult to spot. FMIC plumbing couplings are common spots for leaks especially near the throttle body and at the turbo outlet. I recently discovered one on my turbo... bolt in the compressor housing backed out over time and created a major leak path! Major pain to find it as it was on the underside of the turbo.

Good explanation on the leak test, I have a tester from an old car I had that I just never had to use. I will have to give it a shot next week, I'm going out of town this weekend so no time to play on the caR..
 

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You want single digit LTFT's and preferably low numbers. If you see them creep up in magnitude (negative) under boost, then you have a boost leak to some degree. Even tiny leaks will cause your trims to increase in magnitude as that's your ECU trying to pull fuel to correct for lost metered air. I think the ME7 will throw a code around +/-15% perhaps a bit more.

As for VIDA, there may be a way, but if you go to the screen where you can read out ECU info, it will not show you LTFT as an option, but rather LTFT at idle which is not what you want. I know if you throw a code, VIDA will give you the output for when the code was triggered and it will show you LTFT, but as for reading it in real time, I've not found out how to do that in VIDA... the Torque app does it.
 
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