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Old 11-12-2012, 07:18 PM   #1 (permalink)
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Default Loss in boost... turbo possible culprit?

Ok... first off:

60 trim t3/t4 turbo (about 70,000 miles with some shaft play)
AEM EMS tuned
GM boost solenoid
supporting mods and other stuff bla bla


Ok... so in my AEM my boost target is set at 26psi which for a year or so it hit and never had any problems reaching 26psi and holding. Just recently over the last few months I have noticed a drop in boost pressure... from 24 psi max... to 22psi now to around 19psi. I have tested for a boost leak and dont have any. My AEM is still set at 26 psi but only am able to hit around 19.

Can you guys give me some thought of what would cause a drop in boost pressure. (like I said its not a boost leak)

Could a turbo that has shaft play and seen 60,000 miles of lots of boost slowly start being able to loose its ability to build over 20psi?

Any other ideas of where to look for the demon that eating up my psi?
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05 SRT daily driver
60 trim turbo - 26Psi
Built motor - Eagle, Wiseco, ARP
Supporting fuel
Spec S3+ clutch
AEM EMS tuned

Fastest 1/4 mile: 12.64
Fastest 1/4 speed: 121mph

Last edited by Dasstrum; 11-12-2012 at 07:24 PM.
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Old 11-12-2012, 07:33 PM   #2 (permalink)
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If the turbo doesnt have any fin damage and the shaft play isnt excessive, I would say the turbo is fine.

How high you are going on your boost leak test?
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Old 11-12-2012, 07:43 PM   #3 (permalink)
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Quote: Originally Posted by tunerlover3 View Post
If the turbo doesnt have any fin damage and the shaft play isnt excessive, I would say the turbo is fine.

How high you are going on your boost leak test?

Around 20psi hooked up to my air compressor. I do have a very small boost leak around my blow off valve but it is very small and wouldnt cause a 7psi drop
__________________
05 SRT daily driver
60 trim turbo - 26Psi
Built motor - Eagle, Wiseco, ARP
Supporting fuel
Spec S3+ clutch
AEM EMS tuned

Fastest 1/4 mile: 12.64
Fastest 1/4 speed: 121mph
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Old 11-12-2012, 08:42 PM   #4 (permalink)
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You need to test at least too the boost level you were running (so 26 PSI). I test to 30.
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Old 11-13-2012, 12:31 AM   #5 (permalink)
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The simple things that are most likely to cause drops in boost include a problem with the external wastegate, exhaust leaks pre-turbo and pressure leaks post turbo (of which blow-off valves, especially cheap knock-offs can be problematic). Some simple things you could do would be to get a hand-held vacuum pump/tester that has a gauge and see if the wastegate holds vacuum and if not disassemble and check the condition of the diaphragm. You could also do a visual inspection of the turbo's exhaust housing to manifold flange and the wastegate to manifold flange for signs of carbon from exhaust leaks. It might also be a good idea to try blocking off your blow-off valve temporarily and see if that makes any change (just be sure to let off the throttle slowly as to avoid compressor surge which is already problematic on most 60-trim setups on the SRT-4).

Beyond that and checking basic health of the engine such as doing a compression test there shouldn't be too many other possible causes of the lower boost. If the wastegate tests good you could always try a simple manual boost controller to rule out a problem with your electronic controller. From there it could be possible the turbo is on the way out but most will still build boost without too much of an issue up until there's really excessive shaft play and then they're normally leaking oil past the dynamic seals pretty bad at that point . Also if the car doesn't feel noticeably slower and you're seeing this as a drop in gauge pressure you might data log and see what pressure the MAP sensor is showing to rule out a bad boost gauge.
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Old 11-13-2012, 05:53 PM   #6 (permalink)
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Quote: Originally Posted by blackbird_R/T View Post
The simple things that are most likely to cause drops in boost include a problem with the external wastegate, exhaust leaks pre-turbo and pressure leaks post turbo (of which blow-off valves, especially cheap knock-offs can be problematic). Some simple things you could do would be to get a hand-held vacuum pump/tester that has a gauge and see if the wastegate holds vacuum and if not disassemble and check the condition of the diaphragm. You could also do a visual inspection of the turbo's exhaust housing to manifold flange and the wastegate to manifold flange for signs of carbon from exhaust leaks. It might also be a good idea to try blocking off your blow-off valve temporarily and see if that makes any change (just be sure to let off the throttle slowly as to avoid compressor surge which is already problematic on most 60-trim setups on the SRT-4).

Beyond that and checking basic health of the engine such as doing a compression test there shouldn't be too many other possible causes of the lower boost. If the wastegate tests good you could always try a simple manual boost controller to rule out a problem with your electronic controller. From there it could be possible the turbo is on the way out but most will still build boost without too much of an issue up until there's really excessive shaft play and then they're normally leaking oil past the dynamic seals pretty bad at that point . Also if the car doesn't feel noticeably slower and you're seeing this as a drop in gauge pressure you might data log and see what pressure the MAP sensor is showing to rule out a bad boost gauge.

Holy jebus good information... Thanks... I will try all that
__________________
05 SRT daily driver
60 trim turbo - 26Psi
Built motor - Eagle, Wiseco, ARP
Supporting fuel
Spec S3+ clutch
AEM EMS tuned

Fastest 1/4 mile: 12.64
Fastest 1/4 speed: 121mph
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