Duramax engines have always come with solid turbos. However after miles and miles of whistling and boosting, your turbo may have problems. Or you may have other issues, that make you think your turbo has problems. This is very common as most drivers watch boost, keeping an eye on how much PSI they're making. It stands to reason that if your peak boost drops, your turbo has a problem. This is usually not the case though. More often then not, when we diagnose this symptom we find there are other problems leading to a lower than expected boost number.
Target boost numbers for the following RPO's are as follows (PSI)
2001-2004 LB7- Stock 20-22, tuned 24-26, tuned with PPE boost valve 28-31. Failure will occur near 34psi
2004.5-2016 Stock 22-24, Mild tune 27-28, Hot tune 33-35
The factory map sensor which electronically measures boost on a 2001-2004.5 trucks only reads to 22-24 psi, 2006-2016 MAP sensors read to 37 psi. If you want to read boost numbers higher you'll need an aftermarket gauge.
A common cause of low boost is a boost leak. Boost leaks cause low power, slow spool-up, unresponsive throttles, excessive black smoke and high EGTs. This occurs when part of the charged air system develops a leak. The charged air system includes, intercooler piping, intercooler, y-bridge, ect. The video below will walk you through the proper way to boost test your Duramax. Beware of simply completing a visual inspection. Many leaks happen in places you will not be able to see from a top view of the engine bay. Also, leaks can develop while in boots and will not show themselves unless under load, making it imperative that you pressurize the entire system.
Another common problem is a failed or failing EGR. The Exhaust Gas Recirculation (EGR) system carries inert exhaust gas to the charged air system to lower combustion pressure in the engine. We routinely see EGR's stuck open which bleed exhaust pressure from the turbine and cause low boost and excessive black smoke. It's also common for EGR gasket failures to cause boost leaks. Check out helpful resources like DuramaxForum.com and DieselPlace.com for enthusiast help.
If you have properly diagnosed your truck, and are sure you have no boost leaks and your EGR is not a factor, consider other possible issues impacting total boost. When the humidity rises there is less air molecules to compress, same as when the ambient air temperature rises. The less air you can pull into the truck, the less boost you can make. This is the same issue for trucks in higher altitudes.
If you would like a complete list of Duramax turbo specifications check out the download available below.
