D16Z6 shows 200,000+ on the odo, to my knowledge the motor is stock but has been apart at some point in its life (has ARP head studs)
Came with no history
Couple months ago started running like had a mis-fire pulled the plugs and number 4 was fouled. Not sure if is oil or fuel
Ran compression then and was good. 180psi on all.
Swapped the plugs around and ran better. Was drive able but getting worse.
Month ago I adjusted the valves, new platinum plugs, Plug wires are a year old and look fine. Replaced fuel filter
Soon after check engine light comes on. Still running but like crap.
CEL code 9. Great I thought. Finally an answer! Cylinder sensor!
Replaced distributer with brand new from Napa (expensive) and ran the valves again, expecting an improvement. Nope.
Then this last week another cel, code 1. Oxygen Sensor. This must be it!
I reset computer and drive just to verify 3 times code 1.
Then I get a code 43.
So i'm confident is a bad oxygen sensor. Today $50 for a Bosch, install it and runs worse than ever.
Just checked compression again, 180psi on all four
Here are the plugs tonight. The black plug is #4. Picture is upside down




I really could use your guys help. Could it be valve seals?

 

Swap the fuel injector for that cylinder with one of the others. See if the fouling moves to the new cylinder-- that would mean the injector is bad.

 

I'm gona try this right now...

 

Use denso for the 02 sensor.

 

Your pic link is broken.

 

Or NTK, both are good.

 

Well I swapped the injectors around and so far car is running great. The tips were pretty dirty so I cleaned them up with some carb cleaner. See how it is in a week or so.
Thanks for the help.........

 

Fixed. (i hope)