Overboost ! What could be?
11-28-2015, 04:16 AM
#1
Rennlist Member
Thread Starter
Overboost ! What could be?
Hopefully everybody had a nice thanksgiving!
Would like to find answer for my fault codes. Use the search already but couldnt find a proper answer.
I have several fault codes and maybe someone could give me a hint if they are related and where to start looking for.
Thank you in advance!
The car is a 2005 Turbo S. The truck is running good but comparing to my Cayenne S it should run better.
I am using fuel with 95 octane.
Would like to find answer for my fault codes. Use the search already but couldnt find a proper answer.
I have several fault codes and maybe someone could give me a hint if they are related and where to start looking for.
Thank you in advance!
The car is a 2005 Turbo S. The truck is running good but comparing to my Cayenne S it should run better.
I am using fuel with 95 octane.
11-30-2015, 01:55 PM
#4
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Hi
Porsche.com has the parts PDFs
The pipe to my left hand turbo was broken, from under the turbo v8 cover all the way down to the turbo, it had dropped down onto the under tray.
Stu
Porsche.com has the parts PDFs
The pipe to my left hand turbo was broken, from under the turbo v8 cover all the way down to the turbo, it had dropped down onto the under tray.
Stu
11-30-2015, 03:14 PM
#6
Three Wheelin'
If you have an overboost issue - it's likely related to the waste gates not opening correctly. This can be from the solenoid that opens them, the vac hoses that connect the solenoid to the waste gates, or the waste gates themselves. You could also have a MAP sensor issue registering the incorrect boost pressure. I'd start with the vac hoses first, solenoid, MAP sensor, and then the waste gates themselves. Not sure where the solenoid is on the 957, but getting at the waste gates won't be fun, and you'll need some excellent mirror skills or a boroscope.
For the cams - you probably have a cam sensor problem, or actuator problem. If it were me, I'd try a slightly thicker oil first as the cam actuators are hydraulic, and if you have heavily sheared out oil, you may not have the proper viscosity for actuation.
For the evap code - I'd clear it and see if it comes back. It's an emissions thing and won't impact performance. It could be a gas cap leak, getting gas with the car running, or a simple check valve somewhere.
For the cams - you probably have a cam sensor problem, or actuator problem. If it were me, I'd try a slightly thicker oil first as the cam actuators are hydraulic, and if you have heavily sheared out oil, you may not have the proper viscosity for actuation.
For the evap code - I'd clear it and see if it comes back. It's an emissions thing and won't impact performance. It could be a gas cap leak, getting gas with the car running, or a simple check valve somewhere.
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11-30-2015, 03:39 PM
#8
Rennlist Member
Thread Starter
Great! Thank you everybody for your friendly advise. I will try to go through all these things.
About the codes, they are coming back after i cleared them. The oil i am using is a 5w50. just changed from 5w40. I had a look from under the car now and it seems there is a lot more to do. oil arround the area of the pressure hose. Looks like the seal is gone.
About the codes, they are coming back after i cleared them. The oil i am using is a 5w50. just changed from 5w40. I had a look from under the car now and it seems there is a lot more to do. oil arround the area of the pressure hose. Looks like the seal is gone.
12-01-2015, 12:49 AM
#11
Three Wheelin'
Cyclic valve gets a signal (pressure) from Intake and from the Turbochargers pressure output and then adjusts (cycles) the air to the Wastegates. A small leak in the line from the Turbo (line 10) can cause an overboost. A large leak would cause a short but powerful overboost then overboost protection would cut-in and cause it to go into a limp mode, which a restart would clear but the code would still stay locked in. A small but occasional overboost will still cause a code.
12-01-2015, 07:56 AM
#13
Rennlist Member
Thread Starter
Originally Posted by hahnmgh63
Cyclic valve gets a signal (pressure) from Intake and from the Turbochargers pressure output and then adjusts (cycles) the air to the Wastegates. A small leak in the line from the Turbo (line 10) can cause an overboost. A large leak would cause a short but powerful overboost then overboost protection would cut-in and cause it to go into a limp mode, which a restart would clear but the code would still stay locked in. A small but occasional overboost will still cause a code.
How important is it that all these hoses are installed on their place without being pressured and squeezed. Just ask because under the "turbo cover" is a real crowd of hoses.
Thank you
12-01-2015, 07:45 PM
#14
Three Wheelin'
Line #5 in post #7 goes from the Cyclic valve (known as the N75 valve in the VAG turbocharged world) and Tee's with each end going to one of the Turbocharger wastegates. These have positive pressure, the more pressure (when enough to overcome the default spring pressure) then the wastegate starts to open which starts to release/bypass exhaust gasses from flowing to the Turbine wheel, either slowing (less boost)(mostly open) or keeping the boost steady (partially open). You can check line #5 with a pressure pump to see if it holds, some wastegates can be damaged by apply a vacuum, not sure about the Cayennes so always safe to apply pressure rather than taking the chance with vacuum to see if it holds. 2nd Cyclic line goes to the intake manifold by the throttle body and can be tested with vacuum or pressure on one end and disconnecting and plugging the other end. The 3rd goes to the Compressor side of the Turbo to sense Boost pressure, on Twin-Turbocharged Audi's they Tee this line off both Turbos compressors but looking at the diagram it appears Porsche just takes the pressure reading off of one of the Turbos.
Last edited by hahnmgh63; 12-02-2015 at 07:54 PM.