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Old 08-27-2016, 08:41 AM   #1
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6.0 L needed a "crank relearn"

Hi folks, my '07 2500HD with the 6.0L gas had gotten down to 6.0 MPg according to both the trip computer and back of the receipt calcs. Towing OR unloaded!

I get it... The 6.0 isn't purchased for mileage, but 6mpg was something wrong.

2 weeks ago I had my mechanic install a cold air intake kit and do a full tune up with new plugs and wires. That got me up to 7.5 MPG.

While towing home from last weekends trip to lake Sebago, the truck finally threw a check engine light.

I brought it in, and when they pulled the codes, they found some serious computer problems.



So, they did a crank relearn. Unloaded on a nice 55 mph state route last night I saw 15 mpg! The crank relearn doubled my mileage.

Labor Day is my next tow with the camper. I'm hoping for 10 while towing.


Craig Bailey
New England
2007 Chevy 2500HD crew
2015 Jayco Jayflight 32BHDS
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Old 08-27-2016, 10:07 AM   #2
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Learn something every day, I never heard of a "crank relearn".

My '02' 2500HD 6.0L (sold couple months ago) averaged 7-9 mpg towing depending on tow conditions...., never 6 mpg, but around 12-15 otherwise.

I'll have to watch my new 6.0L going forward and keep the "crank relearn" in mind.

Bob
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Old 08-27-2016, 10:35 AM   #3
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The relearn may relate to variable valve timing and/or injector performance.
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Old 08-27-2016, 11:13 AM   #4
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Originally Posted by RedHorse1 View Post
The relearn may relate to variable valve timing and/or injector performance.
I believe you are correct. When I bought my tuned ECM, I had to take it to a shop with a specific computer to have the crank relearn performed.
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Old 08-27-2016, 02:17 PM   #5
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That's my understanding, too. The computer was unhappy for a spell, so it retarded the timing. When I started fixing issues, the ecm was too far out of "normal"


Craig Bailey
New England
2007 Chevy 2500HD crew
2015 Jayco Jayflight 32BHDS
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Old 08-27-2016, 02:28 PM   #6
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Burning that much gas I suspect your exhaust pipe was black.
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Old 08-28-2016, 12:23 PM   #7
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Burning that much gas I suspect your exhaust pipe was black.


Oddly, there was zero symptom other than the "burning" in my wallet. That's why it took so long to correct; everyone basically wrote off the 6.0 like "you don't buy that for fuel economy HA HA HA!"

But I'm glad I continued "encouraging" my mechanic to keep digging.


Craig Bailey
New England
2007 Chevy 2500HD crew
2015 Jayco Jayflight 32BHDS
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Old 08-28-2016, 05:06 PM   #8
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Oddly, there was zero symptom other than the "burning" in my wallet. That's why it took so long to correct; everyone basically wrote off the 6.0 like "you don't buy that for fuel economy HA HA HA!"

But I'm glad I continued "encouraging" my mechanic to keep digging.


Craig Bailey
New England
2007 Chevy 2500HD crew
2015 Jayco Jayflight 32BHDS
Yeah usually an engine that is running real rich will blacken the inside of the tailpipe.
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