Hey fellas. Another dilemma. So I decided to replace the two downstream CO2 sensors. I accidentally cut the wire for one of the upstream sensors so since I had bought three, one for my other X300, I replaced it also. The car is running great, however I have developed a misfire. I have no Check Engine light on, but I am wondering if the trouble could be that one upstream sensor that I didn't replace. Or are one of my coils about to die. Any ideas?

 

You will eventually get a code. The same thing happened to me after I replaced the sensors. Which ones did you purchase? I am still fighting everything with random codes. I have sent all my injectors to be redone, replaced the coils and plugs, and have a MAS and a new ECU on their way. I have also replaced the fuel regulator and checked all the vacuum hoses. Once I get everything installed, I am hoping for the best.

 

The upstream sensors are there just for a check, so it will not affect the engine's ability to run.

We need to make absolutely sure you did not plug a sensor into a different plug. All four of the oxygen sensors are all the same, and all of the plugs are located in the same spot, so it could be that you mistakenly plugged in Bank B, Downstream Sensor into the Bank A, Downstream Sensor? Is that possible? Maybe you should try to swap the plugs and see what happens?

 

I used the FAE 77185's sent over from Germany. I was super careful not to mix up the connectors since I only wanted to do the job once. The spark plugs are the copper units used as OEM. Should I use another type of plug. Is a coil about to die?

 

Before I replaced the O2 sensors the engine would start to hesitate as if its about to die. I would pull over and shut the engine off. After about 5 minutes I would fire it up and continue the journey. Yesterday after an hour of driving the same thing happened. No codes popped up on my scanner. I wonder if my fuel pump is about to die.

 

Could be. That or the sock filter the fuel pump has could be clogged. There has been at least one post where the vacuum created by the pump would eventually cause a clog, but when shut off, the sock settled and would allow fuel back into the pump before getting turned on again and failing again. How about the fuel filter?

 

Yeah, I was thinking of replacing the Fuel Filter since I have no idea when it was done last.