1998 yukon Mystery p0300 and rough idle still

[OilBurner2003]

I'd look at the pin connections to see if one or more have gotten distorted due to heat, therefor making a poor connection. Look for expanded metal, burn marks, etc. Try closing them up if possible to close on the pins tighter of you see something

Took another look, didn’t find anything out of the ordinary. Will get some fuel trim data for the rest of the guys shortly.

 

[OilBurner2003]

Can you post a recap for us on your scanner readouts? I’d have sworn that you had screenshots in here somewhere but the IFS syndrome may have kicked in on me.

*Fuel trims at idle and at, say, 2000 and 3000 rpm if you’re not able to drive it
*O2 sensor graphs
*Misfire counts by cylinder, idle and raised rpm

Did you fix the broken vacuum lines going to the heater hose water valve and solenoid? Potential vacuum leak…maybe.

Hello sir, this is the data I could get at idle after accelerating to 2000 RPM for a bit. I believe the app is having a bug or two, because I couldn’t get both fuel trims to show at the same time. Idle at this time was around 700.

 

[east302]

Some random unorganized thoughts…

Try graphing the trims to see how they trend when given more throttle. A vacuum leak would usually show positive trims trending to zero with increased throttle - not what you have, though.

Bank 2 looks to be somewhat more of a problem child than the other, and the bank 2 downstream O2 sensor is switching - implies a catalyst issue. A graph on that would help see how it compares to its upstream counterpart.

But, I’m not sure if a clogged converter would cause negative trims (oxygen sensor is reporting too much fuel so computer is cutting injector pulse time to reduce fuel). Hmm. Usually that’s a leaking injector but a valvetrain issue may be another possibility? Sticking valve or lifter maybe? Maybe others can chime in on that?

Have you done a compression test?

Definitely swap the two downstream sensors and compare the voltages. The bank 1 sensor looks to be dead and your testing looks to show good circuitry.

 

[OilBurner2003]

Some random unorganized thoughts…

Try graphing the trims to see how they trend when given more throttle. A vacuum leak would usually show positive trims trending to zero with increased throttle - not what you have, though.

Bank 2 looks to be somewhat more of a problem child than the other, and the bank 2 downstream O2 sensor is switching - implies a catalyst issue. A graph on that would help see how it compares to its upstream counterpart.

But, I’m not sure if a clogged converter would cause negative trims (oxygen sensor is reporting too much fuel so computer is cutting injector pulse time to reduce fuel). Hmm. Usually that’s a leaking injector but a valvetrain issue may be another possibility? Sticking valve or lifter maybe? Maybe others can chime in on that?

Have you done a compression test?

Definitely swap the two downstream sensors and compare the voltages. The bank 1 sensor looks to be dead and your testing looks to show good circuitry.

Will swap the sensors. Wanted to point out quickly that the whole exhaust system (both cats) are brand new, only a couple months old. I have not done a compression test, in my mind misfires on all 8 cylinders indicated probably something that wasn’t mechanical, I’m sure it’s worth a test at this point though. As for the valves, same thing, never tried to test them. Can get them both off pretty quickly if need be though! (Valve covers) I’ll update you guys when I switch the O2 sensors and see what happens. In the meantime, I inspected the wiring harness by the timing cover, wrapped some heat resistant tape around the parts that looked suspect to prevent anything in the future, that’s about all I’ve done today.

 

[OilBurner2003]

Some random unorganized thoughts…

Try graphing the trims to see how they trend when given more throttle. A vacuum leak would usually show positive trims trending to zero with increased throttle - not what you have, though.

Bank 2 looks to be somewhat more of a problem child than the other, and the bank 2 downstream O2 sensor is switching - implies a catalyst issue. A graph on that would help see how it compares to its upstream counterpart.

But, I’m not sure if a clogged converter would cause negative trims (oxygen sensor is reporting too much fuel so computer is cutting injector pulse time to reduce fuel). Hmm. Usually that’s a leaking injector but a valvetrain issue may be another possibility? Sticking valve or lifter maybe? Maybe others can chime in on that?

Have you done a compression test?

Definitely swap the two downstream sensors and compare the voltages. The bank 1 sensor looks to be dead and your testing looks to show good circuitry.

Wanted to fact check something. If a valve wasn’t seating right somewhere between both banks, it wouldn’t effect both banks right? I’d imagine just one cyilender that the valve controls. Someone said they had a valve that wasn’t seating right and caused a misfire on all cyls because it gave the computer a lean reading…? Wanted your guy’s opinion on this.

 

[exp500]

I would like to see Fuel Pressure # While driving Doing fuel trims, Like 2,3,4000 RPM. Add a 6 foot hose to your tester and hold it against windshield with wiper.
The best thing for sticky lifters is adjust valves and clean oil. Diesel eng oil very hi detergent.

 

[OilBurner2003]

I would like to see Fuel Pressure # While driving Doing fuel trims, Like 2,3,4000 RPM. Add a 6 foot hose to your tester and hold it against windshield with wiper.
The best thing for sticky lifters is adjust valves and clean oil. Diesel eng oil very hi detergent.

Not really sure how to adjust valves, I’d have to do a lot of research on them. I’ll take a look!

 

[exp500]

Loosen valve adjuster till noisy counting 1/4 turns till noisy. Tighten in 1/4 turns till not noisy, add 1/2 turn. Engine running.Do one side at a time. There are clips or even clothespins to attach to keep oil spray down, or use cut down valve cover like I do.

 

[OilBurner2003]

Loosen valve adjuster till noisy counting 1/4 turns till noisy. Tighten in 1/4 turns till not noisy, add 1/2 turn. Engine running.Do one side at a time. There are clips or even clothespins to attach to keep oil spray down, or use cut down valve cover like I do.

When I get some extra time I’ll try to do the fuel trims and such for everyone. Not going anywhere until a mechanic has a opening.

 

[OilBurner2003]

Loosen valve adjuster till noisy counting 1/4 turns till noisy. Tighten in 1/4 turns till not noisy, add 1/2 turn. Engine running.Do one side at a time. There are clips or even clothespins to attach to keep oil spray down, or use cut down valve cover like I do.

Wanted to update everyone. Got the truck to a shop downtown, they said they'll have it figured out within a week with their schedule. Funny thing is, they actually offered me a job! So we'll see what they find soon.