Where did I EVER say it cannot exist? Never heard of it means just that I never heard of it. I do feel sorry about you not being able to comprehend the written word. We will try to type slower for you...

 

I cant imagine what **** you've been thro in order to decide to change the pass lock! I wouldve sold the truck!!!

 

With currently 8 H3s, 1 H3t and 1H2 sut all with between 135,000 miles- 265,000 miles we get to see all of the nightmares and are continually surprised with things that should not be possible the way it was designed lol

 

Do you have access to a Tech 2? Would be interested to see what your gas tank pressure is before fueling up, after fueling up and after starting. Also if you have a current or historical code for evap. The tech 2 has been hands down the most important thing we have bought to maintain these trucks

 

no i dont have a tech 2. id love to get my hands on one with the can-d module for a bit of programming though

 

no stored codes but once a week or so it throws a code for high evap flow.

 

Visually inspect the metal EVAP line that goes from the tank along the driverside frame rail. They are infamous for rotting out and even a few small holes will cause that intermediate code. Also, the seating surface for the gas cap rusts and can cause the same issue (we have dealt with both over the past 6 months. We bought a fogging machine to more accurately diagnose these issues but I know most people do not have access to that.

The struggle is, without the right testing equipment its a guessing game unfortunately.

 

Lots of great advice here, and I want to add one more easy and low risk option worth trying.

Full disclosure, I have a 2010 H3T Alpha which is the first year of the flex fuel capability, so the fueling system might be a little different than a 2008. I also have a tune installed, but I experienced the same issues when I had to run on a stock tune for a couple months last year. The rough starts were always more pronounced in colder weather. Then I saw an old post somewhere talking about how these LH8/LH9 engines are really sensitive to gas quality, and the recommendation was to try gas from different vendors. I did this over a period of about 6 months, and I eventually landed on Shell. For some reason it is the only gas my 5.3 likes from a cold start. With every other gas I tried, my truck would stutter and idle low and rough for about 15-30 seconds, and then the issue disappears until the next cold start. After I switched exclusively to Shell about a year ago after the issue has yet to return. There is probably a simple explanation for it, and I wish I knew exactly what it was.

 

https://www.toptiergas.com/

 

I only tested top tier gas from the biggest brands (Chevron, Costco, etc.). Always Premium 92 octane. Only Shell works.