DIESEL EGR & POWER: Just smoke
by Bruce W. Smith
Contrary to what most performance-minded Duramax owners believe, the EGR doesn’t affect horsepower, and it plays an integral role in maximizing both engine life and fuel economy. At least that’s what Rod Halsten a top Duramax diesel tech says.
(Blocking and/or removing the EGR is also a federal violation most companies can’t afford to get caught doing.)
Halsten, an ASE-certified mechanic with more than 20 years experience working on GM diesels, says the Duramax EGR only operates at idle and cruise where it allows “inert gases” into the cylinders so the engine can run leaner for optimum mpg while keeping the combustion chamber cooler and reducing NOx. 
“The EGR is automatically turned off under heavier throttle load and during WOT to maximize power.
“It’s during long idle periods the EGR manifold will collect oily soot,” explains Halsten.
“Extreme soot buildup can cause the EGR valve to stick and affect idle quality. But the EGR system doesn’t affect engine power because that’s all bypassed when the ECM senses 8 to 10 pounds boost or WOT.”
Halsten says to replace the EGR valve when it throws a P0401 (EGR Flow Insufficient) code, which usually doesn’t happen until after 100,000 miles.
Note: Make sure your LMM Duramax has the most recent EGR program flashed by the dealer per the service bulletins.
If the EGR valve needs to replaced, it’s probably time to clean the EGR cooler.
“A clogged EGR cooler will trip both EGR and MAF sensor codes, affecting performance.
So you should remove the EGR cooler when the valve is replaced and give it a thorough cleaning,” advises Halsten.”The process takes a couple hours to do it right.”
Downstream is the DPF filter, which Halsten advises should be checked for flow restriction when the EGR is replaced and the cooler cleaned.
“Most GM service techs can use their diagnostic equipment to check flow in and out of the DPF without touching it.”
If flow is below acceptable levels, cut the DPF out and have it cleaned by a specialty service such as FSX (fsxinc.com) or DPF Regeneration (dpfregeneration.com), which is 3 to 4 times cheaper than having it replaced with a new one.
