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Duramax Third Generation: 2006-2007.5 (LBZ & LLY) Discuss the third generation (2006-2007.5 LBZ & LLY) of the 6.6L Duramax diesel engine & associated components. 2006 LLY engine discussion also belongs in this forum due to the similarities of the 2006 LBZ and the 2006 LLY. Engine related discussion ONLY. is the premier Duramax Diesel Forum on the internet. Registered Users do not see the above ads.
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Old 04-01-2019, 12:27 PM   #1 (permalink)
Gear Grinder
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P0234 Overboost

Hi All,

Having some issues with my 06 LBZ (all stock, MBRP downpipe back 4" straight exhaust). Recently, ive noticed when i go from 0 at WOT and get close to 50 or 60, the truck slows acceleration and seems to lose a ton of power. It also starts to 'screech' very loudly once it gets to this point, sounds like its coming from the exhaust but it is a strange noise. When i let off it will bark very loudly and then sound like a wheeze.

I also get very loud 'barking' when the truck shifts or i let off the accelerator, at any speed and RPM.

I plugged into OBDII and get P0234 (Turbo/Super Charger Overboost Condition) and P0108 (Manifold Absolute Pressure/Barometric Pressure Circuit High Input). These codes seem to clear on their own every 4 or 5 engine cycles, but will always come on when i give it 1/2 or more throttle.

I did a run from 0 to whatever my truck could get up to at WOT, and plotted RPM, speed and boost pressure and fuel rail pressure vs time. Around 10 mph my MAP sensor seems to 'max' out at 29 ish psi and stays there until i let off. The truck would not reach 60 mph. Once i let off, while the screeching noise was happening, it is a very loud bark, almost like a wheeze of some sort. The fuel pressure seemed normal until i let off

I replaced existing MAP with a new Delco MAP, and had the same symptoms, no change at all. So i think i can rule that out.

I logged desired boost vs actual and usually at each shift i get a 10 psi difference (which im assuming is triggering the overboost), although the commanded vs actual vane position is very close to each other.

Not sure what is causing this overboost? Could the baro sensor be bad?

2006 LBZ all stock
MBRP downpipe back 4" straight exhaust

Last edited by OkDually; 04-01-2019 at 12:34 PM. Reason: prefix/sig
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