Physh1

2003 5.3 Tahoe, 225k, only a BB tune, airaid jr intake, oe wires, coils, Delco plugs. Tune up was 5k ago right before smog & passed extremely clean. I installed Bosch o2 sensors as well. Engine doesn't use oil. Intake gaskets done 25k ago. No issues.

A few weeks back, leaving work, the truck started fine & after a few minutes started missing. Not a dead miss but sounded lopey. It has a distinct change in sound/tone/miss when it goes from open loop to closed loop but the sounds & frequency of the misses are erratic.

Scanner showed random misfires on bank 1, #7 was missing more than #'s 1,3, & 5.

Sprayed carb cleaner around the intake...no change...
Pulled vacuum line off FPR...no leaks...
Swapped plugs between cylinders...no changes
Swapped wires between cylinders...no changes
Swapped coils between cylinders...no changes
I changed injectors on all 8 cylinders...no changes
Did a noid light test on all 8 injector wires...all good...
Compression check was ~175 on all 8 cylinders...
Variance between high & low was 6%...well within limits...
Leak down was good...
No bent pushrods or funny valvetrain movements...
Oil pressure good, no coolant missing...

Pulled the plugs...1&2 read a little rich
3,4,5,6 looked normal
7&8 read lean.
(5k ago when I switched plugs all 8 were perfect & probably didn't need changing.)

I have not checked fuel pressure yet...testing that Monday as I had to order a new tester.

I'm thinking my Bosch o2 sensors are having issues...I've read up about them. Any advice? I'm stumped & our mechanic at work has been buried so I've been trying to debug myself when I have a little time. Fuel pump is relatively new...60k miles. Still not discounting that it's crapping out though.
Cameron

dirt track racer 81

iTrader: (45)

Get ac delco o2 sensors. I wouldn't any bosch product in any of my vehicles

03sierraslt

iTrader: (22)

Ya, these trucks are picky about different 02 sensors. Like Tyler suggested I would ditch the Bosch sensors.

kicks_z28

My dad went thru 2 sets of bosch o2 sensors on his 05 silverado until switching back to AcDelco and solved the problem right there. Try that next, no joke

Physh1

Ordered them up...I'll see what happens on Monday.

Ugh...shoulda researched o2's before I bought them.

Lesson learned...

Cameron

06 4.8

iTrader: (5)

Anything on this? My new toy does the same thing

Leegreens

Fuel press reg is common prob on high mile trucks but only probs i've had from a bad one is...hard starting, & when you punch it falls on its face like its running out of gas.. Dunno if that helps.