Where is the oxygen sensor on my car? I have looked from the exhaust manifold to the tailpipe and have not found it yet. Trying to find it to unplug it to see if it is the cause of my troubles.

I have a 1990 740GLE 16v DOHC B234f. The balance shaft belt tensioner came apart (the older original style plastic one) and caused the car to jump time. Bent plenty of valves. Found a head which had just been rebuilt and came out of a wrecked car. Purchased it for less than I could have gotten mine worked on and installed it. I pulled the old head and installed the rebuilt one. Cranks and runs, but has a slight miss and drinking gas way too quickly for the price per gallon! I get better mileage out of my '94 Grand Cherokee Limited all time 4WD! I can unplug the AMM and it does run a little worse, but not much. There is a little canister at the end of my fuel rail that ties into the fuel line and rail with a vaccum hose going from it to the intake. (What is it called?) I can pull the vaccum line off of it and it seems to run a little better, but has a higher idle. I can smell gas in the vaccum line. I have checked and re-checked all of the electrical connectors and vaccum lines. Everything seems to be where it should and connected as it should. My service light comes on every now and then, but my check engine light has not come back on since clearing the codes. The passenger compartment stinks of fuel while driving, but I cannot smell any fuel at all while the car is running and my head all up in the engine compartment. The engine does buck a little while at idle, but smooth out with a little throttle. At highway speeds, the car seems to be holding back a little and I have to really push it to get over 80 mph. It seems to be flooding. The car ran great until it jumped time. I have cleaned the throttle body, but all that seemed to do was just make it idle a little higher. The car did sit up for a couple of months while I was putting off getting it repaired. I have now cleaned the flame trap also, with no luck.

I cleared all the codes in my car, ran it to town and back and then re-checked them. I am now only getting a 3-1-2.

3-1-2
Signal missing for knock-related fuel enrichment
Wiring break between EZK terminal 4 and FI #28

What does this mean? My car is running the same as before, kind of rough and still burning more gas than before the head swap. I unplugged the vaccum line from the Fuel pressure regulator and it ran a little better, and I did smell fuel in the vaccum line. If I unplug the AMM, it runs a little worse, but I can still drive the car down the interstate at 80 mph. It still acts like it is flooding out and I get a lot of hesitation while driving the car. I can drive the car 30 miles and it burns a quarter of a tank of fuel! What gives! Where are all of the Volvo GODS when you need them!