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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 03-12-2019, 05:24 PM   #1 (permalink)
TobyIgo
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Fuel econ flux

ALCON- I have a 2011 Sierra 2500HD 6.6L w/aftermarket K&N cold air intake with OEM MAF sensor.

The scenario is this: I drive to/from Washington D.C. on a weekly basis, approximately 400 miles one way from western NC. Most of the time, I'm cruising between 60-65 mph and getting 21-23 mpg. However, there is a period of time where the bottom drops out of my fuel economy and for about 100-150 miles, I'm only getting 12-14 mpg. Then after a while of really crappy mileage, it starts going back up again. I'm really at a loss here because I have some people telling to swap out my MAF sensor for a performance MAF sensor to complement to the air intake. I have others telling me to delete or bypass the MAF sensor by removing it and allow the O2 sensor to regulate. I'm just totally perplexed why my truck will be getting great mileage and then drop out.

Has anyone else ever experience such an anomaly?

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Toby

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Old 03-12-2019, 05:28 PM   #2 (permalink)
redwngr
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What method are you suing to monitor the fuel economy?

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Old 03-12-2019, 05:39 PM   #3 (permalink)
TobyIgo
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Watching the average on my dash and manual method of calculating gallons used over the course of my trip. When I notice the mpgs dropping rapidly on the dash, I reset to see immediate average and see that it's down in the lower teens (12-14). Then after a while (approximately 100-150 miles), I notice it starting to climb again. I'll hit the reset again and it's back in the 20's (21-23).
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Old 03-12-2019, 06:22 PM   #4 (permalink)
BanksLB7Duramax
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Sounds like it’s regening.
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Old 03-12-2019, 07:04 PM   #5 (permalink)
jacksoea
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Agree with BanksLB7Duramax. Your truck is probably going through a regen cycle. I would imagine that it occurs somewhere close to once every 400-500 miles of driving.


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Old 03-12-2019, 07:37 PM   #6 (permalink)
TobyIgo
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YES! Exactly, about every 400-500, getting great mileage, then the bottom drops out for 100-150 miles, then it picks back up again for another 400-500 miles. So what do I do to stop this regen cycle?
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Old 03-12-2019, 08:13 PM   #7 (permalink)
jacksoea
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Fuel econ flux

You canít stop the regens without deleting the DPF. The regen (regeneration) elevates the exhaust temperature to burn out all the soot from the Diesel Particulate Filter (DPF) installed in your exhaust system.

Once the filter gets sufficiently clogged (high differential pressure), the engine automatically runs at higher RPMs and the 9th injector in the DPF uses additional fuel to raise the exhaust temperature.

If you donít allow the regen to occur you will start to have really high back pressures.

If you delete the DPF then this issue goes away. Keep in mind that the DPF is required by federal law, but do as you please.


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Last edited by jacksoea; 03-12-2019 at 08:14 PM.
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Old 03-12-2019, 08:49 PM   #8 (permalink)
TobyIgo
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After reading your comment, I looked up regen cycles and now I recall my truck going through an announced regen cycle back in the fall. By announced, I mean the computer lit up my dash and let me know what was going on. I drove several hundred miles before this finally cleared from the dash.

So it is possible I'm going through some sort of unannounced regen cycle? Meaning, perhaps the soot buildup in the DPF isn't bad enough to kick in the computer to conduct a full-on regen cycle and my truck and mileage are just suffering the consequences??? I've also read about putting on a bypass filter to help with soot and reduction in the DPF. This mess really sucks because I put the cold air intake on to get better performance, but every 400-500 miles, the gains in fuel efficiency are completely lost.
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Old 03-12-2019, 08:51 PM   #9 (permalink)
holmestransfer
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If the system works as designed, you wonít get a notice that the truck is in regen. The only way to tell is by the fuel mileage lost, and the above described symptoms.


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Old 03-12-2019, 08:56 PM   #10 (permalink)
jacksoea
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Fuel econ flux

Agree with holmestransfer. Your regen occurs automatically in the background. You may notice higher RPMs and maybe a burning smell close to your exhaust because of the high temperatures, but other than that all you will notice is crappy gas mileage.

That being said, if you are not driving the truck long enough or at high enough speeds (i.e. city driving), your truck may not be able to complete the regen. If that happens, you will eventually get a message stating that regen is occurring and that you should continue driving. If you drive far/fast enough, you will most likely never see this message.




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Last edited by jacksoea; 03-12-2019 at 08:57 PM.
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