Losing Boost Help !
Thread Starter
Melting Slicks
Joined: Sep 2007
Posts: 2,134
Likes: 139
From: Port St Lucie Florida
Losing Boost Help !
I have a 2002 A4 corvette D1SC LS6 only seeing around 5lbs of boost on an autometer guage. I know I should be making more than that on a 4.38 pulley especially in cold weather with a crank 7.5 pulley. Anyway I should be making around 10 lbs boost, but the guage is showing only 5lbs. I checked the piping and also got new Fast 102 gaskets which I did not need. No other leaks, I also checked the boost guage and it works so I am thinking its the blow off valve not fully closing. Is their an adjustment screw somewhere? Its very frustrating trying to find this problem. Is bob here? Any help would be great Thanks in advance.
Last edited by corvet786c; Jan 7, 2018 at 12:35 PM.
Burning Brakes
Joined: Sep 2016
Posts: 1,133
Likes: 319
From: Ohio
The things with blowers is that they make what they make. A combination of pulleys doesn't determine a set boost level. A given pair of pulleys will make less boost on a bigger engine and more on a smaller one.
If you're making boost, chances are the blowoff valve is closing. Make sure its not leaking, though.
If you're making boost, chances are the blowoff valve is closing. Make sure its not leaking, though.
Melting Slicks
Joined: Jul 2014
Posts: 2,356
Likes: 359
From: Virginia
Have you done a boost leak test? Quickest and easiest way to make sure its not a boost leak is to pressurize the system with the engine off and spray soapy water around all your couplers and vac hoses. Where you see bubbles, you have a leak.
Thread Starter
Melting Slicks
Joined: Sep 2007
Posts: 2,134
Likes: 139
From: Port St Lucie Florida
Actually today I have, car was running and had a leak around the MAF coupler and lower 45 degree rubber hose, had a pin hole leak at idle.
Thread Starter
Melting Slicks
Joined: Sep 2007
Posts: 2,134
Likes: 139
From: Port St Lucie Florida
Thread Starter
Melting Slicks
Joined: Sep 2007
Posts: 2,134
Likes: 139
From: Port St Lucie Florida
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are you sure the gauge is accurate?... if you are able to log the car you can compare those readings to what the gauge says... just an idea... other than that and what you have already checked, possibly belt slip
Last edited by StingrayRebel; Jan 8, 2018 at 08:55 PM.
Thread Starter
Melting Slicks
Joined: Sep 2007
Posts: 2,134
Likes: 139
From: Port St Lucie Florida
Sprayed windex over MAF and lower passenger side rubber 45 degree hose coming off I/C and at Idle it was bubbling bad, so hoping these would help me get the boost back.
Last edited by corvet786c; Jan 8, 2018 at 09:23 PM.
Melting Slicks
Joined: Jul 2004
Posts: 2,844
Likes: 144
From: Northern Ireland
I didnt ask about major changes...I asked if any changes had been made between it last making the boost you expected...to it now not making boost you expect.
A pinhole is not going to cause it.
So unless there has been a component failure somewhere....you are giving the impression some work has been done...so the cause is likely to lie around that work. You also mention about intake gaskets....so presumably some work has been done around the intake ?
Tech Contributor
Joined: Apr 2007
Posts: 10,924
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From: Forney Texas
As Turpid mentioned, a boost leak test is the best way to isolate your troubles. A&A offers a nice piece to keep your MAF from blowing apart under boost. It works well and it's relatively cheap insurance, especially considering the idea of blowing the MAF apart, being stranded and having to get it towed and then repaired.
For a boost leak test, probably the easiest thing to do is cut out a circle from a piece of wood, like a 2x6 board, the size of the dongle. Insert it into the coupler and clamp it down. Remove your brake booster line and use a compressor and blower nozzle to pressurize the entire system. If your lifters pump down with the valve spring pressure, you won't need to remove any rocker arms to seal it all up. Try to keep the pressure under 20psi. You should be able to isolate your leak pretty easily. If you still have that FAST intake on it, it's the older model and your idle is higher than normal, Remove the intake and look across the bottom rear of it. You'll see a crack running across it. Something I've witnessed a dozen or more times.
For a boost leak test, probably the easiest thing to do is cut out a circle from a piece of wood, like a 2x6 board, the size of the dongle. Insert it into the coupler and clamp it down. Remove your brake booster line and use a compressor and blower nozzle to pressurize the entire system. If your lifters pump down with the valve spring pressure, you won't need to remove any rocker arms to seal it all up. Try to keep the pressure under 20psi. You should be able to isolate your leak pretty easily. If you still have that FAST intake on it, it's the older model and your idle is higher than normal, Remove the intake and look across the bottom rear of it. You'll see a crack running across it. Something I've witnessed a dozen or more times.
Melting Slicks
Joined: Jul 2014
Posts: 2,356
Likes: 359
From: Virginia
Never thought of this method, I always just buy a PVC pipe cap that fits inside the turbo inlet coupler, drill and tap it for a barb fitting and then I use that to pressurize. Both would work, just interesting to see how others have MacGuyver'ed the boost leak test.
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Melting Slicks
Joined: Sep 2007
Posts: 2,134
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From: Port St Lucie Florida
I wanna thank everyone for their suggestions and comments, but especially Neutron82.
I fixed it, It wasn't a major leak at all, I mean still needed those 2 45's rubber elbows, but my problem was belt slippage. The car was serviced 6 months ago with a new green back belt, well by now it was broken in and needed to be tighned because it was slipping. On the A&A newer bracket I have it in the middle on the green back, Is this ok? I don't want to brake another tensioner again.
Got my 2 lbs back and the car rips, like it is supposed to.
I fixed it, It wasn't a major leak at all, I mean still needed those 2 45's rubber elbows, but my problem was belt slippage. The car was serviced 6 months ago with a new green back belt, well by now it was broken in and needed to be tighned because it was slipping. On the A&A newer bracket I have it in the middle on the green back, Is this ok? I don't want to brake another tensioner again.
Got my 2 lbs back and the car rips, like it is supposed to.