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Duramax Fifth Generation: 2011-2016 (LML) Discuss the fifth generation (2011-2016) of the 6.6L Duramax diesel engine & associated components. Engine related discussion ONLY.

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Old 06-23-2019, 10:02 PM   #1 (permalink)
Chrisgid4
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2011 lml idling problem

2011 lml cp3 conversion cat filter truck runs great when idling I rev up the engine and it will stall when idling down at around 1000 rpms truck almost dies out

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2011 lml duramax
cp3 conversion, cat filter
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Old 06-24-2019, 08:11 PM   #2 (permalink)
lynn1130
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That's not really much info to go on. Did you do the conversion, and when? You are running a Cat filter but has the filter head been rebuilt? How long ago was the filter changed? Do you have a lift pump? Tuner?

It sounds like fuel starvation but we need some help determining what has been done to the truck to give some suggestions as to what to look at.

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Old 06-24-2019, 09:01 PM   #3 (permalink)
Chrisgid4
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No lift pump just rebuilt the filter head with a merchant kit an the cat upgrade was done about a week ago I had a shop do the tune they told me it was a tow tune by kory it also has a cp3 pump the pump and the tune was installed about 3 years ago
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Old 06-25-2019, 09:58 AM   #4 (permalink)
Rvn4me
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If this just accured after filter head with a merchant kit and the cat upgrade was done. One of these is your cause.

Is the pump staying hard or does it go soft.
If you still have air, your Adapter might need more tightening.

This is common losing prime after CAT filter installation or other filters.
https://www.dieselplace.com/forum/3-...tallation.html

Fuel Supply and Fuel Filter Housing

The fuel filter housing is on the suction side (there is not a supply pump from the factory) and are prone to suck air.
Install fuel vacuum test tool.
Prime the fuel system with the hand primer until 10 PSI is indicated on the gauge, check for external leaks and repair. If the pressure drops from 10 PSI to 2 PSI in less than 1 minute, remove the fuel outlet line from the filter and cap it. Remove the ignition 1 relay and crank the engine for 2 – 15 second intervals, the high pressure pump should pull at least 12 inches of Hg vacuum. If air gets into the system it will cause a false/low reading.
Install clear hoses at the inlet and outlet of the fuel filter housing. Re-prime the system and then start the engine, there should be very little air going into or coming out of the fuel filter housing.
Common air ingestion places are the filter housing, drain valve, rubber hoses and quick connections. You need to use clear lines to isolate where the air is coming from and work your way back toward the tank until you don’t have any more air coming through the clear line. Unless you know where to get the tool that sees through black rubber lines to find air, your only other option is to bounce around and replace parts.
In some cases the “Filter Life Indicator” will be triggered prematurely, sometimes within 1000-5000 miles after changing the fuel filter. If this problem occurs even though the fuel filter is not restricted, it can be caused by excessive leakage on the high pressure side of the fuel system or other supply side issues. Verify there is no air in the supply system and restriction is not excessive under all load conditions. If these things check ok, diagnose the high pressure side as if there is low rail pressure codes. It seems that fuel flow is calculated in the ECM and is used to calculate fuel filter life. If the calculated flow is high, the ECM assumes a larger quantity of fuel has been filtered.

Use a vacuum gauge to check the suction side of the fuel system. You should have no more than 5 inches Hg at WOT (wide open throttle) or 7-8 inches Hg under load. If you still have too much restriction after changing the filter, check for collapsing soft fuel lines by the drivers side valve cover and under the truck near the transmission. The fuel tank pick up may also be plugged. Too little vacuum (less than 2 inches Hg) means that it could be sucking air.

What are your Balance Rates, when checked hot in park or neutral, should indicate bad injectors. Any injectors that are more than +4/-6.9

Last edited by Rvn4me; 06-25-2019 at 10:20 AM.
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