Hi All. I have had my 99 XJ8 119k for about six months, I have replaced the radiator, then had to have the Gear Box rebuilt. When I picked it up it had a rough idle. The shop pulled the Codes and got a P0172 system running rich Bank 1. I have since changed to spark plugs and checked for vacuum leaks. I didn't find any. Question? Could the transmission shop have installed the o2 sensors (upstream and downstream) in the wrong locations causing the car to run too rich? What should I look at doing next to find the problem?
I have code p0172 CEL and Restricted performance - rough idle and sluggish
The engine was running perfectly when I dropped it off



99 XJ8 119k

 

I think you may be on the right track, but I would bet the sensors are more likely swapped left to right rather than front to back.

Other than fuel regulator problems or leaky injectors, the shop manual lists the following:
ECM receiving incorrect signal from one or more of the following components:
ECTS, MAFS, IATS, TPS

They cold have messed with any of these cables, of course. It should be easy to diagnose O2 sensor reversal by watching the fuel trims. - One stuck high and the other low. Of couser, the code will prevent the ECM from actually entering closed loop control, so it will take a little diagnostic effort to be sure.

 

Do you mean they may have crossed the o2 sensors during installation, putting the one from the right side onto the left side? If so I'm thinking about switching them to the opposite sides to see if that make a difference

 

Now I'm getting P0300 random misfire and P0172 bank 1. I tried rebooting system by touching the negative post to positive for a few minutes but that doesn't seem to work. I assumed the CEL would go off until the code misfire reappears. When I do that the CEL & restricted performance light is immediately illuminated. Does the reboot not temporarily erase CEL codes?


99 XJ8 VDP 119k

 

Before or after switching leads? This could come from bad connections or swapped O2 leads.

 

The upstream O2 sensors on mine have a gray connector and the downstream (after cat) have a black connector, if that's any help. They are different. They may have got them swapped side to side as Sparkenzap said though. You really need to get a OBDII reader though, like an UltraGauge, so you can see the fuel trims in real time. I'm not sure of any other way to tell if the cables have been swapped.

 

Sparkenzap you hit it right on the head. I finally had time to switch the o2 sensor connections left to right and now the kitty is purring again. I could have easily damaged the catalyc converters. I will never use that shop again. I hope this helps someone else who has a similar problem

 

Glad you got it, but don't be too harsh on the shop UNLESS you took it back and they coyuldn't/ wouldn't fix it. It is extremely easy to swap the wires and it is not immediately noticeable on a test drive.