please help at end of rope!!!

[mikemedic3]

Finally found the problem!

Well took the truck to the garage, I was at a loss. To recap;
Check engine light came on and had MAF code, changed the MAF and still had code with a lean code also. The truck also began to have a rough idle while in gear. So after research determined it was the intake gasket, so I changed that.
Now no more MAF code but was getting a 171,161 if memory serves correct which was bank 1,2 sensor 2 heater circ. malfunction, and still had rough idle in gear, and occasional 304 code for misfire cylinder 4. So I checked fuel pressure, which was ok, changed after cat o2's with no change, checked fuses which were ok. Climbed underneath to search wires and did find bank 1 sensor 2 pink wire broken, so I respliced, still to get heater malfunction code and rough idle when in gear. At this point I gave up and took it to the garage.
Well they found the fuse to the o2 sensors blown, and a bad plug in cylinder 4. Now I checked the fuses, removed them and retested them, so only thing it could be is that it must have popped ofter I respliced the pink wire. Now with all the other codes that I was getting and seeing it more or less happened all at the same time I did not check the plug believing it was a lean issue all along. I figured initially the lean and misfire codes for that cylinder were from the vaccum leak in that area.
Having a vaccum leak, bad plug and broken wire for the o2 sensor all within a short enough time to overlap cost me 150 in labor!!!! However it is real nice to have the truck running smooth again!!!!
I post this for anyone else having similar issues, so you are sure to always start with the basics, and don't rule out two different issues that happened simultaneously!!!!!

 

[madmike]

Been in the same situation Mike, I replaced the intake gasket and o2 sensors and MAF and still misfiring. Fuel pressure fine here also. Regulator also working fine.

Just a couple of items for anyone checking this thread... a hole/crack in the cold air intake duct between the MAF and throttle body will also cause a misfire code and condition as well as still show bad MAF code at times or have a vacuum sounding leak. Something I learned to check also, from another mechanic but it didn't solve my issues.

Also for those saying heater codes are not related to engine misfire, what Mike was referring to was the o2 sensors in the 2003 yukon have heating elements in them and that was what he was referring to, not the heater inside the cab of the truck.

Thanks for the info on the o2 fuses. Will have to check those to see if that is part of my problem on my misfires. I did see that my open loop went to closed loop when I replaced the o2 sensors, but still showing lean condition one the left bank. Will check that next.