My problems began in June with a blown head gasket resulting in milkshake oil. I pulled the head, had it rebuilt. The bottom half was in beautiful shape so I pressed on and decided to replaced everything I could get my hands on while it was apart … all hoses, new radiator, starter, injector harness … etc … etc. The whole project went surprisingly well and except for several sheared bolts on the water rail was rather enjoyable (I am lucky enough to have an air-conditioned garage and that REALLY helped )
Next my power steering pump started leaking so it was either $250 for a rebuilt unit or $12 for a seal kit. I opted for the kit and other than getting at the inner pump mounting bolt that worked out fine. Of course then my P/S RACK started to leak at the top of the tower and I had to pull it and install a new/rebuilt unit.
Next I noticed a vibration in my driveshaft when I had it up on a lift replacing my catalytic converter (more on that later). So I took it home and put the rear of the car up on jacks, removed the driveshaft and had it rebalanced. While I had the car up I decided to pull out the gas tank to repair a pesky leak on the very top near the vent tube … and why not change the diff fluid while I’m at it.
All of this worked out well and the car now runs, smells, and handles like a dream … EXCEPT …
I have a check engine light Code 4 (O2 sensor system full rich) that I can’t figure out !
As previously mentioned I replaced the font catalytic converter and installed a new O2 sensor. no change. So I had the emissions checked at the tailpipe and it did in fact show a slight over rich situation.
So I guess this tells me that the O2 sensor is actually doing it’s job and telling the ECU (engine control unit) that there really is a rich fuel situation and therefore it’s not a false alarm.
So why is it running rich ? That’s the question. Since the ECU controls everything there’s no adjustments that I know of.
Any ideas ?? The crazy thing about these early computer cars is that they have just enough smarts to tell you something’s wrong but not enough to tell you what it is. The later XJ40s (1990 on) are a little better but still nothing compared to modern cars with OBDII