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'05 Duramax 6.6 LLY PO299

P

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New to the Forum. I have a 2005 Pony Express Motorhome on a C5500 Kodiak chassis with a 6.6 LLY Duramax and Allison trans bone stock with 46,000 mi. While driving, the CEL comes on and the engine loses power. The scanner reads a PO299, turbo underboost, that's the only code it shows. The engine won't rev over 2500rpm and barely make 50mph.I can erase the code while driving and the power comes back immediatley. There is no smoke from the exhaust.The CEL will come on randomly. It doesn't matter if its under load or cruising. Could it be a bad sensor? Most threads I've read guys had power adders causing the problem but this is stock.
 
Possibly a bad boost sensor, but I have only heard of a handful failing. I would check your boost tubes for any rub spots where they might be losing boost, or a cracked rubber boot.
 
See if the boot came loose or off on the intercooler. If so then clean the overlap joint real well, dry it, spray it with some hair spray and put it back together. Not joking. Drivers side boots get oily from the egr and can come loose. A common problem.
 
Electronics are always the 2nd place to look. Assume the computer is telling the truth with functioning sensors until you prove otherwise. Start with the air filter and check for boost leaks including holes or a split intercooler. Also check gaskets where the EGR joins the intake. Mice like to use air filters as nests on stored vehicles.

You could have exhaust issues like a crushed pipe or leaks.

You are entering limp mode to protect the engine when the under boost code triggers.
 
WarWagon said:
Electronics are always the 2nd place to look. Assume the computer is telling the truth with functioning sensors until you prove otherwise. Start with the air filter and check for boost leaks including holes or a split intercooler. Also check gaskets where the EGR joins the intake. Mice like to use air filters as nests on stored vehicles.

You could have exhaust issues like a crushed pipe or leaks.

You are entering limp mode to protect the engine when the under boost code triggers.
Click to expand...

WarWagon we recently replaced leaky exhaust manifold gaskets. Everything else is OK.

Thefermanator the hoses and tubes to the intercooler were checked and tightened.
boost sensor is that on the drivers side of the intake manifold ?

BtFarm I wondered what I could use to seal them, I'll give it a try.
 
I'm not sure on the MD trucks, but I know pickups had problems with the intercooler piping getting holes rubbed in them by the power steering pump. I think(not sure on an MD truck) that the boost sensor will be on the passenger side of the engine mounted up close to where the intake goes into the engine. The one the drivers side in a pickup is a atmospheric pressure sensor to tell the ECM what altitude you are at. Have you hooked up a scanner and watched teh boost reading to see what it is doing?
 
THEFERMANATOR said:
I'm not sure on the MD trucks, but I know pickups had problems with the intercooler piping getting holes rubbed in them by the power steering pump. I think(not sure on an MD truck) that the boost sensor will be on the passenger side of the engine mounted up close to where the intake goes into the engine. The one the drivers side in a pickup is a atmospheric pressure sensor to tell the ECM what altitude you are at. Have you hooked up a scanner and watched teh boost reading to see what it is doing?
Click to expand...

All I have is a basic Actron, read and delete codes. I'm waiting for a Tech II. Untill it's available I'll be looking for the obvious. Will let you know what I find, until then thanks for the replys all.
 
Finally got results. We found a stuck exhaust brake. (It was stuck in the closed position) The butterfly and shaft were stuck solid. Piston worked OK. I think I used that brake maybe twice since I've had the truck. It's activated by a toggle on the dash. Maybe I should leave it on all the time. Replaced the unit and everything is good since.
 
Thanks for the update and good news. :thumbsup: Keep checking in here and keep us up on your rig and activities.
 
Glad you got it fixed. The stuck brake would explain the manifold gasket leaks... Should have mentioned a possible plugged kitty as well.
 
exahust brake fix I had same

pop pop said:
New to the Forum. I have a 2005 Pony Express Motorhome on a C5500 Kodiak chassis with a 6.6 LLY Duramax and Allison trans bone stock with 46,000 mi. While driving, the CEL comes on and the engine loses power. The scanner reads a PO299, turbo underboost, that's the only code it shows. The engine won't rev over 2500rpm and barely make 50mph.I can erase the code while driving and the power comes back immediatley. There is no smoke from the exhaust.The CEL will come on randomly. It doesn't matter if its under load or cruising. Could it be a bad sensor? Most threads I've read guys had power adders causing the problem but this is stock.
Click to expand...
I had same thing go wrong got it free with a lot of pen.oil then clamped a pair of large vicegrips on it to act as a counter weigh when it is deactivated works great .I leave EB on all the time.
 
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