Hi everyone! Been visiting this site since I got my new-old rig in 2016, learning repair/mechanics as I go so thanks to everyone that's posted help and troubleshooting tips here!

This is more of an FYI, thinking it might help someone. A couple months ago I started getting bad valve chatter under load, coinciding with an occasional hesitation, general loss-of-power, and lower MPG. I was also getting a intermittent CEL code 21 (heated O2 sensor). I did a couple rounds of valve adjustments, a snug 008 and 012, but nothing changed. I suspected that maybe either burnt valve or poor ignition was making for poor combustion conditions, maybe affecting O2 sensor reading (though I think I see the fault in that logic now). Anyway, checked/cleaned grounds, pulled plugs, timed ignition, Ohm'd plug wires, all that. Nothing. Did not pull head.

I know I should have Ohm'd out the sensor, but since the service history is so sketchy on this truck (and since I have to work on this thing in short intervals) I decided just to order up the $50 Denso OEM part. I noticed someone on here said to change that part every 75,000 or something regardless of CEL.

Installed it, code cleared, valve chatter WAY down (but not gone), and acceleration is noticeably stronger and smoother. MPG TBA.

Thing is, the O2 sensor I pulled is not only non-Denso (can read some numbers, but no brand/mfr), it's not even the right shape! From a quick image-search, it looks a lot like the Bosch universal sensors.

So in brief: always diagnose, but also if you're not the original owner, who knows what cheap electronic part some shop/owner threw at your truck.

 

I am glad the Oxygen sensor fixed your issue. I am not entirely sure how it helped the engine noise. My best guess is that the oxygen sensor is reading correctly now and allowing the computer to calculate the correct air-fuel ratio, which allows for better combustion.