turbo codes

[robp823]

When you get the typical turbo boost performance codes when you hear that popping through the intake and then the puffs of black smoke is that the egr valve opening as kind of a saftey feature from too much boost?

[DamageINC]

That surging/flutter noise you're hearing when you let off the gas is the audible result of there not really being an external boost bypass (or a blow-off valve). The VGT is designed so that a bypass system isn't necessary but when they get all sticky inside, they can't function normally.

 

The issue is that when you let off the gas and the rpm's tank waaaaay down, the turbo is still spinning at 100,000+ rpm. There's still boost being created for a small period of time. Plus, there, is still residual boost left in the CAC tubes, CAC, and Intake as well. But the engine cannot use the amount of air that's trying to be forced down it's throat now that the rpm's have dropped so heavily, and this air literally 'rebounds' back out of the intake, through the CAC, and then off of the impeller fins in the turbo's compressor housing. And it continues to "bounce" around in the system until the pressure has alleviated and the impeller has slowed down enough.

 

This is also not good for overall turbo longevity, as this event will slow down the turbo MUCH faster than it's intended to, and this loads the bearings in a way that they weren't really designed to be loaded and will eventually result in excessive radial end-play. But, as it turns out, when this problem occurs, you may very well be replacing the turbo (or at least the center-section) anyway for other reasons.

 

 

Dave

[robp823]

well i get that pop noise through the intake on hard accel somtimes not letting off the throttle i know what you are talking about when you let off and hear that flutter but this noise is a pop on accell and if you look out the rear view mirrir everytime you hear it it puffs black smoke out the tail pipe

[Keith Browning]

is that the egr valve opening as kind of a saftey feature from too much boost?

That is correct and an IDS data recording will prove it. Dave described the source of the noise fairly accurately but your question leads me to believe that you have a stuck or sticking turbocharger. When boost raises to approximately 26 PSI under acceleration and PCM has backed off on the VGT actuator duty cycle and realizes manifold gage pressure is still climbing it will momentarily open the EGR valve to bleed off some exhaust pressure in an attempt to slow down the turbo. This action will continue until the turbo slows and boost reduces or the driver lets off of the accelerator.

 

You wont find this documented anywhere. Trust me, I have searched but it is part of the PCM strategy as you suspect.

 

I have seen stuck turbos cause this but don't rule out EP sensor issues that can make a turbo malfunction. Diagnosis always begins with verifying the pressure sensors for correlation and bias. EP, MAP and BARO... but we have new built in tests on IDS for checking the turbo including Turbo Boost and VGT test for 2004 and newer engines.

[DamageINC]

well i get that pop noise through the intake on hard accel somtimes not letting off the throttle i know what you are talking about when you let off and hear that flutter but this noise is a pop on accell and if you look out the rear view mirrir everytime you hear it it puffs black smoke out the tail pipe

Ohhhhhh, hehe ok. Well, Keith took care of the question for ya then /forums/images/%%GRAEMLIN_URL%%/smile.gif

 

*goes and sulks in corner*

 

Dave

[robp823]

thanks guys for all the help