Slight miss but 6 mpg!!? Need help

[Chetty mo]

Hi guys thanks for the add to the group. I’m having a real hard time trying to figure out what’s wrong with my 2008 GMC Yukon XL 5.3 4 x 4. I have a slight miss but no codes. I replaced everything in the evap system. Purge valve. Charcoal canister. Vapor canister vent valve. (Pump at gas station kept stopping while filling up). I tried a new throttle body. No change. I put new air filter in. I have a smoke machine. I have a creader scanner 123E. Any help would be greatly appreciated.

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[Fless]

With your scanner, monitor and document your short- and long-term fuel trims at idle and at about 1500 rpm.

Also, when it's warmed up a little check that the upstream O2 sensors (B1S1, B2S1) are switching from about 0.1v to 0.9v.

Check your misfire counters; a decent scanner will have a counter for each cylinder.

 

[Chetty mo]

With your scanner, monitor and document your short- and long-term fuel trims at idle and at about 1500 rpm.

Also, when it's warmed up a little check that the upstream O2 sensors (B1S1, B2S1) are switching from about 0.1v to 0.9v.

Check your misfire counters; a decent scanner will have a counter for each cylinder.

Yes I have been taking my scanner with me on my landscaping route and watching the fuel trims. They look fine. My o2’s also look fine at about 750 to 850. I added a pic of something I don’t understand. The throttle position numbers in the red.

 

[Chetty mo]

With your scanner, monitor and document your short- and long-term fuel trims at idle and at about 1500 rpm.

Also, when it's warmed up a little check that the upstream O2 sensors (B1S1, B2S1) are switching from about 0.1v to 0.9v.

Check your misfire counters; a decent scanner will have a counter for each cylinder.

Also not showing anything for the misfire data. 0 which seems odd since I can feel it when accelerating and while sitting at a light. But not all the time very intermittent.

 

[Chetty mo]

Hi guys thanks for the add to the group. I’m having a real hard time trying to figure out what’s wrong with my 2008 GMC Yukon XL 5.3 4 x 4. I have a slight miss but no codes. I replaced everything in the evap system. Purge valve. Charcoal canister. Vapor canister vent valve. (Pump at gas station kept stopping while filling up). I tried a new throttle body. No change. I put new air filter in. New throttle body sensor. I have a smoke machine. I have a creader scanner 123E. Any help would be greatly appreciated.

 

[wjburken]

Do you have the ability to read fuel trims and O2 sensor values?

 

[Chetty mo]

Yes. I have a decent scanner.

 

[Chetty mo]

Do you have the ability to read fuel trims and O2 sensor values?

Yes I have a decent scanner.

 

[Chetty mo]

Yes I have a decent scanner.

 

[Chetty mo]

Do you have the ability to read fuel trims and O2 sensor values?