Time to upgrade the LML (opinions wanted) - Page 2 - Chevy and GMC Duramax Diesel Forum
11-16 LML Performance Parts Discussion Discussion of Performance Parts For the 2011 to 2016 LML Duramax Trucks No Advertising

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post #11 of 14 (permalink) Old 11-13-2019, 07:04 PM
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Originally Posted by Zach_LML View Post
emissions components on vacation.
Phrase of the week.

DPF/SCR technology summarized in three words: It doesn't work.
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post #12 of 14 (permalink) Old 11-14-2019, 11:21 AM
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…………………...…...…...…………………...……

Wrong. Totally wrong. It happens that my local GM dealer organization has a long history & reputation of of "trying to do the right thing" for its customers. Which explains why they get so much "repeat business" even tho costs are higher than some guy working out of his back-yard.

I will not bore you with example after example where they COULD have taken advantage of my ignorance, but elected to show me the most economical way out.

Yes - I "get it"....some of you have the misfortune to be in areas where the service writers are just salespeople ( who I wouldn't trust/allow to competently change the spark plugs on my lawn mower ! ).

In my case, it was the techs at my local dealership who (quietly and "off-the-record") recommended both certain "adjustments" to my pollution controls AND who suggested a CP3 conversion should be considered mandatory to anyone who is both "out of warranty" AND who use their trucks as trucks, especially in rural areas where help may be a long walk away in ugly weather.
Against my better judgment, im going to try to explain again how this CP4 problem can be both a common failure, and an uncommon failure at the same time. Kind of like special relativity, it all comes down to perspective.

You have 3 samples of people to take data from. You have 10,000 people in each sample.

the first 10,000 are regular joes and joets who dont use forums, dont modify there trucks, and just drive them for a few years and trade up. These people are very unlikely to see a failure in the CP4 pump as they are 1, unlikely to have the truck long term, and 2, are unlikely to abuse it. These people are your average consumer making up the majority of your ownership base.

The second 10,000 are people from this forum. Forums are a collection of knowledge and a place for people of like interests to collaborate. This is going to attract people seeking help with problems. These people are going to report a higher than average failure rate, since the fact that they have a fuel system problem is likely to drive them to the forum for answers which skews your poll results and makes them appear to have a higher failure rate compared to your first group of standard owners. Even this group though only reports a 12% failure rate over 100K miles.

Your last group is 10,000 diesel mechanics at chevy dealerships. These guys spend all day long doing nothing but fixing broken trucks, so they are even more unintentionally biased than the previous group since the odds of a truck without problems rolling into there bay is basically 0. This group is much more likely to see a failure rate higher than the 12% we see on this forum, since they spend all day every day fixing this and other problems.

From these three examples you can see how with the same actual real world failure rate, you can spin the results to your liking based on who you sample for data. The media does this every day, its not a new thing. On one hand, GM can say they have a low failure rate because the average owner is likely to never see a failure. A law firm looking to make a buck could take the second sample of data to make the problem look much worse then it is . and the dealership, while maybe not intentionally misleading you, would use the third data sample as it is the one that is "most valid" to there experience.

The fact though is that the first group is by large the majority in the real world, followed by the second, and with GM diesel techs making up the minority.

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post #13 of 14 (permalink) Old 11-14-2019, 01:20 PM
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Against my better judgment, im going to try to explain again how this CP4 problem can be both a common failure, and an uncommon failure at the same time. Kind of like special relativity, it all comes down to perspective.

You have 3 samples of people to take data from. You have 10,000 people in each sample.

the first 10,000 are regular joes and joets who dont use forums, dont modify there trucks, and just drive them for a few years and trade up. These people are very unlikely to see a failure in the CP4 pump as they are 1, unlikely to have the truck long term, and 2, are unlikely to abuse it. These people are your average consumer making up the majority of your ownership base.

The second 10,000 are people from this forum. Forums are a collection of knowledge and a place for people of like interests to collaborate. This is going to attract people seeking help with problems. These people are going to report a higher than average failure rate, since the fact that they have a fuel system problem is likely to drive them to the forum for answers which skews your poll results and makes them appear to have a higher failure rate compared to your first group of standard owners. Even this group though only reports a 12% failure rate over 100K miles.

Your last group is 10,000 diesel mechanics at chevy dealerships. These guys spend all day long doing nothing but fixing broken trucks, so they are even more unintentionally biased than the previous group since the odds of a truck without problems rolling into there bay is basically 0. This group is much more likely to see a failure rate higher than the 12% we see on this forum, since they spend all day every day fixing this and other problems.

From these three examples you can see how with the same actual real world failure rate, you can spin the results to your liking based on who you sample for data. The media does this every day, its not a new thing. On one hand, GM can say they have a low failure rate because the average owner is likely to never see a failure. A law firm looking to make a buck could take the second sample of data to make the problem look much worse then it is . and the dealership, while maybe not intentionally misleading you, would use the third data sample as it is the one that is "most valid" to there experience.

The fact though is that the first group is by large the majority in the real world, followed by the second, and with GM diesel techs making up the minority.

You pretty much hit this one perfectly, no sensible way to argue with this.
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post #14 of 14 (permalink) Old 11-14-2019, 01:37 PM
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Originally Posted by J83 View Post
Against my better judgment, im going to try to explain again how this CP4 problem can be both a common failure, and an uncommon failure at the same time. Kind of like special relativity, it all comes down to perspective.



You have 3 samples of people to take data from. You have 10,000 people in each sample.



the first 10,000 are regular joes and joets who dont use forums, dont modify there trucks, and just drive them for a few years and trade up. These people are very unlikely to see a failure in the CP4 pump as they are 1, unlikely to have the truck long term, and 2, are unlikely to abuse it. These people are your average consumer making up the majority of your ownership base.



The second 10,000 are people from this forum. Forums are a collection of knowledge and a place for people of like interests to collaborate. This is going to attract people seeking help with problems. These people are going to report a higher than average failure rate, since the fact that they have a fuel system problem is likely to drive them to the forum for answers which skews your poll results and makes them appear to have a higher failure rate compared to your first group of standard owners. Even this group though only reports a 12% failure rate over 100K miles.



Your last group is 10,000 diesel mechanics at chevy dealerships. These guys spend all day long doing nothing but fixing broken trucks, so they are even more unintentionally biased than the previous group since the odds of a truck without problems rolling into there bay is basically 0. This group is much more likely to see a failure rate higher than the 12% we see on this forum, since they spend all day every day fixing this and other problems.



From these three examples you can see how with the same actual real world failure rate, you can spin the results to your liking based on who you sample for data. The media does this every day, its not a new thing. On one hand, GM can say they have a low failure rate because the average owner is likely to never see a failure. A law firm looking to make a buck could take the second sample of data to make the problem look much worse then it is . and the dealership, while maybe not intentionally misleading you, would use the third data sample as it is the one that is "most valid" to there experience.



The fact though is that the first group is by large the majority in the real world, followed by the second, and with GM diesel techs making up the minority.


Selection bias.

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