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P0234 Overboost/ No Power

 
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Old 03-05-2019, 10:24 AM
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P0234 Overboost/ No Power

07 CGT 80k miles. The only code in VCDS is P0234 (turbocharger overboost condition). It always sets somewhere between 3700 and 4k RPM at 100% load. The car makes very little power anywhere over around 3 or 3.5k RPM. It can be floored on the highway and I will watch the tach slowly increase from 4k RPM while it barely accelerates; it almost feels like a clogged cat.

I fear that it is a major problem with the turbo. Maybe it is the vacuum lines, but it has no other codes and the trims look fine. My next move was going to be to figure out what PIDs I need to log to calculate boost, and then drive around data logging with VCDS to see how much boost it is making under various conditions. Does this sound like the right approach, any ideas? Thanks
 
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Old 03-05-2019, 01:29 PM
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We are all sorry to hear this. Attached is a short explanation of possible culprits. Also included a photograph of a Bentley Turbo. This is not an easy one to diagnose. A bad catalytic converter would throw other codes.

Indeed there are a couple solenoids that control vacuum to the diaphragm that can fail. Usually these throw separate codes, sometimes not.

This posting is a starting point to help start a conversation. Certainly we would like to help you and learn more.



The difficulty in diagnosing this could be something simple albeit hard to find. The easiest but unlikely culprit could be one of the rubber hoses to the intercooler is collapsed.

Wondering if the loss of power is the ECM going into limp mode to protect the engine?
 

Last edited by 1eapplebaum; 03-05-2019 at 01:35 PM.
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Old 03-05-2019, 01:49 PM
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In my humble opinion monitoring the turbo pressure is only going to confirm what is happening. Worth a try, deeper diagnosis will most certainly be necessary.
 
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Old 03-05-2019, 04:37 PM
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Thanks for the ideas. I do not think the ECM is putting it into limp home mode, there is no MIL (or other dash lights) and the car always feels the same even right after clearing all codes. My plan to monitor boost was just to confirm lack of boost and try to narrow it down because I don't really know what to try next.
 
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Old 03-05-2019, 08:59 PM
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I did some data logging with VCDS. Here is a 2nd gear pull with a little before and after driving. It looks like the computer might be pulling boost due to the over boost condition (but I have no other signs of anything like limp home mode). After just driving it, I can confirm that the power really falls off right around 4k RPM.

 
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Old 03-05-2019, 09:23 PM
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The first evaluation is to take off the under shield and make sure that one of the intercooler rubber tubes isn't collapsed or pinched. Probably not the case but if it is, bingo. Easy things first.

One of the wastegate dump valves can fail, a collapsed diaphragm. Or the electronic sensor on the diaphragm is kaput. There are elektro vacuum solenoids that control the wastegate dump valves, can go bad .This is not an easy one. Should one of the wastegate stay closed overboost will occur. There's a possibility the turbo vanes are dirty that will cause overboost.

The long-shot is a collapsed intercooler tube. If This were my car I'd go underneath and check the two rubber tubes the right and left. Take each one off at the bottom see how much oil comes out. Hopefully there's no aluminum with it. Oil usually has collected at the rubber hose outlet to the iintercoolers.

Might as well take an inspection camera and look at the turbo vanes when the rubber hoses are off
 

Last edited by 1eapplebaum; 03-05-2019 at 09:27 PM.
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Old 03-05-2019, 10:13 PM
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Great, thanks. I will check the intercooler hoses tomorrow and try to take a look with the inspection camera. I think some of the other things can be tested in VCDS. The weird thing is that if the boost figures are accurate, I should have good power at the higher RPMs. I think I will try to log that same data for the other side tomorrow, if one side is different than the other that could narrow your list down and explain the lack of power. I will report back tomorrow.
 
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Old 03-06-2019, 07:23 AM
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The figures point towards blockage. At first blush that is encouraging. Essentially there is boost creating back pressure. That would explain no power. Possibly also explain the DTC code.
 
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Old 03-06-2019, 03:01 PM
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Both intercooler tubes look fine. The inside of the passenger intercooler looks super clean, slight oil residue on the tube, but not one drop. The driver side had 2 or 3 oz of oil plus metal shavings (I am 90% sure that these are fine metal shavings and not some other crap), plus the inside of the intercooler is covered in oil. I was planning on sticking the camera up there, but I took a break when I saw the metal shavings.
 
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Old 03-06-2019, 04:30 PM
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Take a magnet to the metal shavings, see if they stick, that would be steel.

Probably aluminum shavings pointing to impeller beginning to disintegrate. Sometimes the oily residue has little shiny aluminum shavings, we don't like to see that. Shouldn't be any shavings. Oil accumulation is normal since the intercooler is a condensate trap for oil mist that circulates inside a working engine.
 
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Old 03-06-2019, 07:13 PM
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The metal is not magnetic. The below pic was out of focus, but it gives an idea of how much metal was at the bottom of the red cup I poured the 3oz of oil from the driver side into. I snaked the camera up the intercooler tubes and into the intercoolers but all I was able to really see was the inside of the intercooler (passenger side clean, driver side covered in oil).



 
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Old 03-06-2019, 07:35 PM
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To inspect the turbo impeller will require removing the driver side air box. Insert the inspection camera down the aluminum induction tube and see the impeller blade. It will go down and curve towards the rear of the vehicle.

This would be the next logical next step.
 

Last edited by 1eapplebaum; 03-06-2019 at 07:51 PM.
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Old 03-06-2019, 07:55 PM
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The camera gets covered in so much oil going the bottom way I could not see anything. I will go from above tomorrow. Thanks for all the help
 
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Old 03-06-2019, 08:08 PM
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At some point that oil needs to be cleaned out. Eventually the oil makes it way into the intake manifold and gets things messy. The oil is one of the reasons mass airflow sensors and throttle bodys become contaminated.

We can deal with this later. Just wanted to put out a FYI.

Bon nuit.
 
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Old 03-07-2019, 11:42 AM
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I cleaned up the oil the best I could and closed up everything underneath the car. Now I feel like an idiot but I can't get the air box out. It looks like there might be 2 screws that come up from the bottom that hold it on right above the MAF (I removed the 2 bolts visible from above, took the top off and removed the filter). I wish there was more info/ DIY guides available for Bentleys. The frustrating part is that I just bought this out of state and it passed the PPI (I think they just charged the battery cleared codes and never drove it above 4k RPM to trigger the overboost code).
 

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